BNL, Upton, Long Island, New York
PVI, Oxnard
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Electron clouds have been observed in many accelerators, including RHIC at BNL. They can limit the machine performance through pressure degradation, beam instabilities or incoherent emittance growth. The formation of electron clouds can be suppressed with beam pipe surfaces that have low secondary electron yield. Also, high wall resistivity in accelerators can result in unacceptably high ohmic heating levels for superconducting magnets. These are concerns RHIC, as its vacuum chamber in the superconducting dipoles is made from relatively high resistivity 316LN stainless steel. The high resistivity can be addressed with a copper (Cu) coating; a reduction in the secondary electron yield can be achieved with a titanium nitride (TiN) or amorphous carbon (a-C) coating. Applying such coatings in an already constructed machine is rather challenging. We sta rted developing a robotic plasma deposition technique for in-situ coating of long, small diameter tubes. The technique entails fabricating a device comprising of staged magnetrons and/or cathodic arcs mounted on a mobile mole for deposition of about 5 μm (a few skin depths) of Cu followed by about 0.1 μm of TiN (or a-C).
INFN/LNS, Catania
During the last 10 years it was demonstrated that slight variations of microwave frequency used in ECRIS strongly influence their performances either for extracted current and for beam brightness and stability. Theoretical investigations put in evidence that such frequency tuning is linked to the electromagnetic field structure inside the resonant cavity. On this basis, we carried out PIC simulations, showing that the frequency tuning has a global influence on plasma properties and on beam brightness. Such analysis allowed the design of the optimum setup for plasma chamber dimensions and microwave injection, to achieve higher currents and better emittances. The magnetic field is based on the use of steep gradient but the cryogenics issues are simplified; the extraction system is designed to minimize the aberrations. The overall dimensions of the MISHA source (Multicharged Ion Source for HAdrontherapy) have been chosen as a compromise between the ideal size for microwave to plasma interaction, the need to get long ion confinement time and the request of getting a compact ECRIS. The description of the source design will be given, along with the expected performances.
INFN/LNS, Catania
The trend of ECRIS to higher frequencies and magnetic fields is driven by the need to have higher beam currents and higher charge states for nuclear physics accelerators. Anyway, because of the limits imposed by the magnets’ and microwaves generator’s technology, any further increase of performances requires a detailed investigation of the plasma dynamics. The experiments have shown that the current, the charge states and even the beam shape change by slightly varying the microwave frequency (frequency tuning effect - FTE). Moreover, for last generation ECRIS, electron energies up to 2 MeV have been detected, depending mainly on the magnetic field structure and gradient distribution over the ECR surface. The plasma dynamics have been studied by means of single particle and PIC simulations: they explain the FTE in terms of the wave field distribution over the ECR surface and the existence of high energy electrons due to diffusion in the velocity space above the stochastic barrier. Other methods used to improve the ECRIS performances, e.g. the two frequency heating with an adequate phase relation between the two waves, can be exploited by means of the simulations.
Kyoto ICR, Uji, Kyoto
We are aiming to develop a compact accelerator based neutron source using Li(p,n) reaction. The first target is a small and high current H+ ion source as an injector of the neutron source. The demands are not only being small and high current but also longer MTBF and large ratio of H+ to molecular ions such as H2+ or H3+. Therefore, the ECR ion source with permanent magnets is selected as such an ion source. Because ECR ion sources don't have hot cathodes, longer MTBF is expected. Furthermore, they can provide high H+ ratio because of their high electron temperature. Using permanent magnets makes the ion source small and running cost low. Up to now, we have measured ion beam current on the first model of the ECR ion source, and fabricated the redesigned model. The data measured of the second model will be presented.
NSCL, East Lansing, Michigan
Funding: Supported by the National Science Foundation under grant PHY-0110253
The construction of the SUperconducting Source for Ions (SUSI), a 3rd generation Superconducting ECR ion source for the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University has been completed and commissioning of the source is ongoing. SUSI operates primarily at 18GHz and is scheduled to replace the 6.4 GHz SC-ECR for injection in the coupled cyclotron later this year. Excellent performances during commissioning have been obtained with SUSI for the production of highly charged ions for both metallic and gas elements and will be presented. A set of six solenoid coils gives SUSI the capability to modify the length and the position of the resonant zone and also to adjust the gradient of the axial magnetic field near the resonance. The impact of this flexible magnetic field profile on the ion beam production and the charge state distribution is actively studied and will be discussed. Emittance measurements of the ion beam extracted from SUSI have been performed and will also be presented.
Muons, Inc, Batavia
UMD, College Park, Maryland
ORNL, Oak Ridge, Tennessee
Funding: Supported in part by the US DOE Contract DE-AC05-00OR22725
Spallation neutron source user facilities require reliable, intense beams of protons. The technique of H- charge exchange injection into a storage ring or synchrotron can provide the needed beam currents, but may be limited by the ion sources that have currents and reliability that do not meet future requirements and emittances that are too large for efficient acceleration. In this project we are developing an H- source which will synthesize the most important developments in the field of negative ion sources to provide high current, small emittance, good lifetime, high reliability, and power efficiency. We describe planned modifications to the present external antenna source at SNS that involve: 1) replacing the present 2 MHz plasma-forming solenoid antenna with a 60 MHz saddle-type antenna and 2) replacing the permanent multicusp magnet with a weaker electro-magnet, in order to increase the plasma density near the outlet aperture. The SNS test stand will then be used to verify simulations of this approach that indicate significant improvements in H- output current and efficiency, where lower RF power will allow higher duty factor, longer source lifetime, and/or better reliability.
ORNL, Oak Ridge, Tennessee
ORNL RAD, Oak Ridge, Tennessee
Funding: The work at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC, was performed under contract DE-AC05-00OR2275 for the US Department of Energy.
The U.S. Spallation Neutron Source (SNS) is an accelerator-based, pulsed neutron-scattering facility, currently in the process of ramping up neutron production. In order to insure that we will meet our operational commitments as well as provide for future facility upgrades with high reliability, we have developed an RF-driven, H- ion source based on a ceramic aluminum nitride (AlN) plasma chamber*. This source is expected to enter service as the SNS neutron production source starting in 2009. This report details the design of the production source which features an AlN plasma chamber, 2-layer external antenna, cooled-multicusp magnet array, Cs2CrO4 cesium system and a Molybdenum plasma ignition gun. Performance of the production source both on the SNS accelerator and SNS test stand is reported. The source has also been designed to accommodate an elemental Cs system with an external reservoir which has demonstrated unanalyzed beam currents up to ~100mA (60Hz, 1ms) on the SNS ion source test stand.
*R.F. Welton, et al., “Next Generation Ion Sources for the SNS”, Proceedings of the 1st Conference on Negative Ion Beams and Sources, Aix-en-Provence, France, 2008
ORNL, Oak Ridge, Tennessee
LANL, Los Alamos, New Mexico
Funding: Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U. S. Department of Energy
Plasmas produced by helicon wave excitation typically develop higher densities, particularly near the radial plasma core, at lower operating pressures and RF powers than plasmas produced using traditional inductive RF coupling methods. Approximately two years ago we received funding to develop an H- ion source based on helicon wave coupling. Our approach was to combine an existing high-density, hydrogen helicon plasma generator developed at ORNL for the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) project with the SNS external antenna H- source. To date we have achieved plasma densities >1013 e/cm3 inside the ion source using <10kW of RF power and <5 SCCM of H2 gas flow. This report discusses the first cesiated H- beam current extraction measurements from the source.
DESY, Hamburg
JLAB, Newport News, Virginia
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
In this contribution, we report progress on the development of a hybrid lead/niobium superconducting RF (SRF) photoinjector. The goal of this effort is to build a Nb injector with the superconducting cathode made of lead, which demonstrated in the past superior quantum efficiency (QE) compared to Nb Three prototype hybrid devices, consisting of an all-niobium cavity with an arc-deposited spot of lead in the cathode region, have been constructed and tested. We present the cold test results of these cavities with and without lead.
Pulsar Physics, Eindhoven
TUE, Eindhoven
Delft University of Technology, Opto-electronic Section, Delft
Three different S-band rf-photoguns have been constructed by Eindhoven University of Technology in the Netherlands: A 1.5-cell, a 100 Hz 1.6-cell, and a 2.6-cell. They share a design concept that differs from the ‘standard’ BNL-gun in many aspects: Individual cells are clamped and not brazed saving valuable manufacturing time and allowing damaged parts to be replaced individually. The inner geometry employs axial incoupling, inspired by DESY, to eliminate any non-cylindrically symmetric modes. Elliptical irises, identical to a 2.6-cell design of Strathclyde University, reduce the maximum field on the irises and thereby reduce electrical breakdown problems. The manufacturing process uses single-point diamond turning based on a micrometer-precise design. The overall precision is such that the clamped cavities are spot-on resonance and have near-perfect field balance without the need for any post-production tuning. Operational performance of the three Dutch rf-photoguns will be presented.
LBNL, Berkeley, California
LLNL, Livermore, California
Funding: Supported by the US DOE at LBNL and LLNL under contracts DE-AC02-05CH11231 and DE-AC52-07NA27344, LARP, SciDAC, and ComPASS. Computuational resources of the NERSC were employed.
It has been shown* that the ratio of longest to shortest space and time scales of a system of two or more components crossing at relativistic velocities is not invariant under Lorentz transformation. This implies the existence of a frame of reference minimizing an aggregate measure of the ratio of space and time scales. It was demonstrated that this translated into a reduction by orders of magnitude in computer simulation run times, using methods based on first principles (e.g., Particle-In-Cell), for particle acceleration devices and for problems such as: free electron laser, laser-plasma accelerator, and particle beams interacting with electron clouds. Since then, speed-ups ranging from 75 to more than four orders of magnitude have been reported for the simulation of either scaled or reduced models of the above-cited problems. In ** it was shown that to achieve full benefits of the calculation in a boosted frame, some of the standard numerical techniques needed to be revised. The theory behind the speed-up of numerical simulation in a boosted frame, latest developments of numerical methods, and example applications with new opportunities that they offer are all presented.
* J.-L. Vay, Phys. Rev. Lett. 98, 130405 (2007).
**J.-L. Vay, Phys. of Plasmas 14, 1 (2008).
SLAC, Menlo Park, California
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
USC, Los Angeles, California
Funding: Work supported in part by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
Recent progress in generating gradients in the 10's of GV/m range with beam driven plasmas has renewed interest in developing a linear collider based on this technology. This talk will explore possible configurations of such a machine, discuss the key demonstrations and the facilities needed to advance this effort and highlight possible alternative uses of this technology.
ANL, Argonne
IIT, Chicago, Illinois
Tech-X, Boulder, Colorado
Funding: DOE. OHEP
We are modeling breakdown arcs in rf structures with Particle in Cell, (OOPIC Pro and VORPAL), Molecular Dynamics (HyDyn, LAMMPS), and an integrated radiation-magnetohyrodynamic package (HEIGHTS) to evaluate the basic parameters and mechanisms of rf discharges. We are evaluating the size, density, species temperature, radiation levels and other properties, to determine how the breakdown trigger works, what the growth times of the discharge are, effects of strong magnetic fields and what happens to both the arc and cavity energy. The goal is to have a complete picture of the plasma and its interaction with the wall. While we expect that these calculations will help guide further experimental studies, we have recently benchmarked model predictions against available experimental data on rise times of x ray pulses, and found a reasonable agreement.
INFN/LNF, Frascati (Roma)
Istituto Nazionale di Fisica Nucleare, Milano
INFN-Pisa, Pisa
UNIPI, Pisa
CNR/IPP, Pisa
INFN-Cagliari, Monserrato (Cagliari)
The PLASMONX project foresees the installation at LNF of a 0.2 PW (6 J, 30 fs pulse) Ti:Sa laser system FLAME (Frascati Laser for Acceleration and Multidisciplinary Experiments) to operate in close connection with the existent SPARC electron photo-injector, allowing for advanced laser/e-beam interaction experiments. Among the foreseen scientific activities, a Thomson scattering experiment between the SPARC electron bunch and the high power laser will be performed and a new dedicated beamline is foreseen for such experiments. The beam lines transporting the beam to the interaction chamber with the laser have been designed, and the IP region geometry has been fixed. The electron final focusing system, featuring a quadrupole triplet and large radius solenoid magnet (ensuring an e-beam waist of {10}-15 microns) as well as the whole interaction chamber layout have been defined. The optical transfer line issues: transport up to the interaction, tight focusing, diagnostics, fine positioning, have been solved within the final design. The building hosting the laser has been completed; delivering and installation of the laser,as beam lines elements are now being completed.
LBNL, Berkeley, California
Funding: This work is supported by NA22 of NNSA under the Department of Energy contract No. DE-AC02-05CH11231.
Active neutron interrogation has been demonstrated to be an effective method of detecting shielded fissile material. A fast fall-time/fast pulsing neutron generator is needed primarily for differential die-away technique (DDA) interrogation systems. A compact neutron generator, currently being developed in Lawrence Berkeley National Laboratory, employs an array of 0.25-mm-dia apertures (instead of one 5-mm-dia aperture) such that gating the beamlets can be done with low voltage and a small gap to achieve sub-microsecond ion beam fall time and low background neutrons. The system will aim at both high and low beam current applications. We have designed and fabricated an array of 16 apertures (4x4) for a beam extraction experiment. Our preliminary results showed that, using a gating voltage of less than 800 V and a gap distance of 1 mm, the fall time of extracted ion beam pulses is less than 1 ms at various beam energies ranging between 200 eV to 600 eV. More experimental results with an array of 20×20 apertures will be presented.
BNL, Upton, Long Island, New York
Funding: Department Of Energy
Under certain assumptions and simplifications, we studied a few physics processes of Coherent Electron Cooling using analytical approach. In the modulation process, the effect due to merging the ion beam with the electron beam is studied under single kick approximation. In the FEL amplifier, we studied the amplification of the electron density modulation using 1D analytical approach. Both the electron charge density and the phase space density are derived in the frequency domain. The solutions are then transformed into the space domain through Fast Fourier Transformation (FFT).
UCLA, Los Angeles, California
Instituto Superior Tecnico, Lisbon
Funding: Fundacao Calouste Gulbenkian and Fundacao para a Ciencia e Tecnologia under grants SFRH/BD/35749/2007.
The possibility of using a CO2 laser (10 micron wavelength) to drive a plasma density compression and achieve effective ion acceleration in gaseous targets (density>~ 1019cm-3) is explored. A parameter scan is performed with a set of particle in cell simulations in OSIRIS*, both in 2D and 3D, for various laser intensities, linear/circular polarization pulses, and plasma densities. Results show that, to generate the shock compression, plasma density must be increased above the critical value to account for the relativistic motion of the electrons. Under these conditions, 2-5MeV ions are observed with moderate intensity (a0=3) laser pulses. Finally, configurations to generate a shock structure are suggested, that will more efficiently accelerate the particles. This scenario is also of particular relevance to fast-ignition, inertial confinement fusion, and implications to those regimes can be obtained from numerical simulations by using the appropriate density normalization.
*R. A. Fonseca et al, LNCS 2329, III-342, Springer-Verlag, (2002)
LBNL, Berkeley, California
PPPL, Princeton, New Jersey
Funding: This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Recent changes to the NDCX beamline offer the promise of higher current compressed bunches, with correspondingly larger fluences, delivered to the target plane for ion-beam driven warm dense matter experiments. We report modeling and commissioning results of the upgraded NDCX beamline that includes a new induction bunching module with approximately twice the volt-seconds and greater tuning flexibility, combined with a longer neutralized drift compression channel.
LBNL, Berkeley, California
LLNL, Livermore, California
Funding: This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Longitudinally compressed ion beam pulses are currently employed in ion-beam based warm dense matter studies. Compression arises from an imposed time-dependent longitudinal velocity ramp followed by drift in a neutralized channel. Chromatic aberrations in the final focusing system arising from this chirp increase the attainable beam spot and reduce the effective fluence on target. We report recent work on fast correction optics that remove the time-dependent beam envelope divergence and minimizes the beam spot on target. We present models of the optical element design and predicted ion beam fluence, as well as benchtop measurements of pulsed waveforms and response.
PPPL, Princeton, New Jersey
Funding: Research supported by the U. S. Department of Energy.
This paper presents a survey of the present theoretical understanding based on advanced analytical and numerical studies of collective interactions and instabilities for intense one-component ion beams, and for intense ion beams propagating through background plasma. The topics include: discussion of the condition for quiescent beam propagation over long distances; the electrostatic Harris instability and the transverse electromagnetic Weibel instability in highly anisotropic, one-component ion beams; and the dipole-mode, electron-ion two-stream instability (electron cloud instability) driven by an unwanted component of background electrons. For an intense ion beam propagating through a charge-neutralizing background plasma, the topics include: the electrostatic electron-ion two-stream instability; the multispecies electromagnetic Weibel instability; and the effects of a velocity tilt on reducing two-stream instability growth rates. Operating regimes are identified where the possible deleterious effects of collective processes on beam quality are minimized.
PPPL, Princeton, New Jersey
LBNL, Berkeley, California
Funding: Research Supported by US Department of Energy.
Plasma are a source of unbound electrons for charge netralizing intense heavy ion beams to focus them to a small spot size and compress their axial length. To produce long plasma columns, sources based upon ferroelectric ceramics with large dielectric coefficients have been developed. The source utilizes the ferroelectric ceramic BaTiO3 to form metal plasma. The drift tube inner surface of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic material. High voltage (~8kV) is applied between the drift tube and the front surface of the ceramics. A BaTiO3 source comprised of five 20-cm-long sources has been tested and characterized, producing relatively uniform plasma in the 5x1010 cm-3 density range. The source has been integrated into the NDCX device for charge neutralization and beam compression experiments. Initial beam compression experiment yielded current compression ratios ~ 120. Recently, an additional 1 meter long source was fabricated to produce a 2 meter source for NDCX compression experiments. Present research is developing higher density sources to support beam compression experiments for high density physics applications.
INFN/LASA, Segrate (MI)
Istituto Nazionale di Fisica Nucleare, Milano
INFN-Roma II, Roma
INFN/LNF, Frascati (Roma)
High vacuum has always been mandatory in particle accelerator. This is true especially for circular machine, where the beam make thousands or millions turns, and beam lifetime is heavily affected by the residual gas scattering. In dimensioning the interaction chamber for a plasma accelerator experiment, because of gas needed and the diagnostics and control devices foreseen, the problem of the effect of the residual gas on the beam arose. Simulation of the beam interaction with the residual gas in the chamber has been performed with FLUKA code. The effects of different vacuum levels on the electron beam is reported and consequences on the beam quality in linacs is discussed.
CIAE, Beijing
Department of Physics, Central China Normal University, Wuhan
Light II-A pulsed power generator was used as a power driver of pumping KrF laser at CIAE. The redesign of Light II-A pulsed power generator is based on the consideration that the machine will consist of one single Marx generator with two different experimental lines，which is presented in this paper. The original experimental line with characteristic impedance of 5Ω is remained, and a new line of low impedance (about 1.5Ω ) is added to the Marx generator. The structure design and the electric insulation design are introduced. It is also outlined here the manipulation of modeling the dynamic behavior of gas discharge arc as well as the circuit simulation results of the two experimental lines. Meanwhile a brief introduction is given to the potential application of the low impedance line.
CAEP/IFP, Mainyang, Sichuan
Funding: Hongtao Li is with the Institute of Fluid Physics, China Academy of Engineering Physics (CAEP), Mianyang City, Sichuan, China. (Fax:86-816-2282695; e-mail: lht680526@ 21cn.com).
In order to study the physics of fast Z-pinches and research the key issues of pulse power technology, a 10MA/6MV z-pinch primary test stand (PTS) composed of 24 modules will be built in IFP. The prototype module adopted capacitive storage scheme is composed of the 6MV/300kJ Marx-generator (MG), intermediate storage capacitor (IC), laser-triggered switch (LTS), pulse forming line (PFL), water self-breakdown switch (WS), and tri-plate pulse transmission line (PTL). The measured output current of the prototype is approximate 520kA, and output voltage is approximate 2.1MV. The unique multi-stage LTS based on uniform field distribution design and multi-pin unsymmetrical WS make the prototype modules have low systemic delay jitter which is necessary for synchronization of multi-module facility. 1-δ jitter of delay of the system is less than 4ns.
CERN, Geneva
The modification of microwave signals passing through an electron cloud can be used as a diagnostic tool for detecting its presence and as a measure for its effective density. This observation method was demonstrated in pioneering measurements at the CERN SPS in 2003 with protons and at PEP-II in 2006 with positron beams in the particle accelerator field. Results and applications of this technique are discussed as well as limitations and possible difficulties. A strong enhancement of the electron related signals due to cyclotron resonance is theoretically predicted and has been observed in different machines. The application of this method can also be extended for space applications and plasma physics where microwave diagnostics is known and used since many years. The question whether suitably chosen microwaves might also be employed for electron-cloud suppression will be addressed. An electron cloud may also emit microwaves itself and the intensity of this emission depends on external parameters such as the electrical bias field and resonator frequencies related to trapped mode resonances in a beam-pipe.
RIKEN Nishina Center, Wako
Significant progress has been achieved since first ECR ion source was developed more than three decades ago and it became one of the best ion sources for heavy ion accelerators in the world. Such progress has been mainly due to utilization of higher microwave frequency and stronger magnetic confinement, technical innovations, and understanding of the production mechanisms of highly charged heavy ions in ECR plasma. Especially, in the last decade, the progress is strongly dependent on advances in the superconducting magnet technology and understanding of the Physics of ECR plasma. Very recently, as the interest in the radioactive beam for research in various fields grows, the need for more intense beam of highly charged heavy ions to inject into the accelerator requires new innovation to improve the ECR ion source performance. In this contribution, I will present the progress of the technology and physics of ECR ion sources. Based on these results, the concepts for next generation ECR ion source for meet the requirements will be presented.
ORNL RAD, Oak Ridge, Tennessee
ORNL, Oak Ridge, Tennessee
Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
Over the past year the performance of the LBNL H- source has been improved to routinely produce 36 mA when averaged over 0.7 ms long pulses at 60 Hz, measured at the RFQ output of the Spallation Neutron Source accelerator. This is up from 25-30 mA during early 2008, and up from {10}-20 mA during 2007. Some of the recent gain was achieved with refined conditioning and cesiation procedures, which now yield peak performance within 8 hours of starting a source change. The ~10 mg released Cs is sufficient for 3 weeks of operation without significant degradation. Another recent gain comes from the elevated Cs collar temperature, which was gradually implemented to probe its impact on the performance lifetime. In addition, load resistors improve the voltage stability of the electron dump and the lenses, which now can be more finely tuned. The achieved gain allowed for lowering the RF power to ~50 kW for improved reliability. A beam current of 38 mA is required at SNS for producing neutrons with a proton beam power of 1.4 MW. In one case, after 12 days of 4% duty factor operation, 56 mA were demonstrated with 60 kW of RF power. This is close to the 59 mA required for 3 MW operations.
SLAC, Menlo Park, California
Funding: Work supported by the DOE under contract DE-AC02-76SF00515
An L-band (1.3 GHz), normal-conducting, five-cell, standing-wave cavity that was built as a prototype capture accelerator for the ILC is being high-power processed at SLAC. The goal is to demonstrate stable operation at 15 MV/m with 1 msec, 5 Hz pulses and the cavity immersed in a 0.5 T solenoidal magnetic field. This paper summarizes the performance that was ultimately achieved and describes a novel analysis of the modal content of the stored energy in the cavity after a breakdown to determine on which iris it occurred.
IAP/RAS, Nizhny Novgorod
Yale University, Physics Department, New Haven, CT
Yale University, Beam Physics Laboratory, New Haven, Connecticut
Funding: Research sponsored by US Department of Energy, Office of High Energy Physics
Experimental investigations of an active Ka-band microwave pulse compressor are presented. The compressor is based on a running wave three mirror quasi-optical resonator utilizing a diffraction grating whose channels embody plasma discharge tubes as the active switch. The principle of compression is based on quickly changing the output coupling coefficient (Q-switching) by initiating plasma discharges in the grating channels. Excitation of the resonator was achieved with a few 100 kW of 34.29 GHz microwaves in 700 nS pulses from the magnicon in the Yae Ka-band Test Facility. A power gain of at least 7:1 in the compressed pulse with a duration of 10-15 nS was achieved.
SLAC, Menlo Park, California
CERN, Geneva
Funding: Work supported by the DOE under contract DE-AC02-76SF00515.
Plasma Wake-Field Acceleration (PWFA) has demonstrated acceleration gradients above 50 GeV/m. Simulations have shown drive/witness bunch configurations that yield small energy spreads in the accelerated witness bunch and high energy transfer efficiency from the drive bunch to the witness bunch, ranging from 30% for a Gaussian drive bunch to 95% for bunch with triangular shaped longitudinal profile. These results open the opportunity for a linear collider that could be compact, efficient and more cost effective than the present microwave technologies. A concept of a PWFA-based Linear Collider (PWFA-LC) has been developed by the PWFA collaboration. Here we will describe the conceptual design and optimization of the drive beam, which includes the drive beam linac and distribution system. We apply experience of the CLIC drive beam design and demonstration in the CLIC Test Facility (CTF3) to this study. We discuss parameter optimization of the drive beam linac structure and evaluate the drive linac efficiency in terms of the drive beam distribution scheme and the klystron / modulator requirements.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
USC, Los Angeles, California
Funding: Work supported by the DOE under contract DE-AC02-76SF00515.
Plasma Wake-Field Acceleration (PWFA) has demonstrated acceleration gradients above 50 GeV/m. Simulations have shown drive/witness bunch configurations that yield small energy spreads in the accelerated witness bunch and high energy transfer efficiency from the drive bunch to the witness bunch, ranging from 30% for a Gaussian drive bunch to 95% for shaped longitudinal profile. These results open the opportunity for a linear collider that could be compact, efficient and more cost effective that the present microwave technologies. A concept of a PWFA-based Linear Collider (PWFA-LC) has been developed and is described in this paper. The scheme of the drive beam generation and distribution, requirements on the plasma cells, and optimization of the interaction region parameters are described in detail. The research and development steps, necessary for further development of the concept, are also outlined.
Instituto Superior Tecnico, Lisbon
UCLA, Los Angeles, California
Funding: F.C.Gulbenkian, F.C.T. [SFRH/BD/35749/2007, SFRH/BD/39523/2007, PTDC/FIS/66823/2006 (Portugal)], and European Community (project EuroLeap, contract #028514)
It is now accepted that self-trapped electrons in a laser wakefield accelerator operating in the "bubble" regime undergo strong periodic oscillations about the wakefield axis because of the focusing force provided by the ions. This betatron motion of the off-axis electrons results in the emission of x-ray radiation strongly peaked in the forward direction. Even though the x-rays are broadband with a synchrotron-like spectrum, their brightness can be quite high because of their short pulse duration and strong collimation. We employ particle tracking in particle in cell simulations with OSIRIS*, combined with a post-processing radiation diagnostic, to evaluate the features of the radiation mechanisms of accelerated electrons in LWFA experiments. We show and discuss results for a 1.5 GeV laser wakefield accelerator stage. A study of the angular dependence of the radiated power is also presented and compared with theoretical models. This analysis also allows for the direct calculation of the radiation losses of the self-injected bunch.
*R. A. Fonseca et al, LNCS 2329, III-342, Springer-Verlag, (2002)
KERI, Changwon
The electron injection into the acceleration phase of the laser wakefield accelerator(LWFA) the key issues for the stable operation of the LWFA. For the controlled electron injection, a sharp downward electron density transition is one candidate. When the laser pulse pass the sharp electron density transition, the electron from the high density region is injected into the acceleration phase. For this injection scheme, a very sharp electron density transition, the distance of the density change must be shorter than the plasma wavelength, is needed. A shock structure of plamsa generated at the gas target is one candidate for such a sharp electron density tarnsition structure. To find out the feasible condition of the density structure, the electorn density was measured by an interferometer with different time. A 200 ps, 100 mJ laser was used to generated plasma. A frequency doubled femto-second laser was used as a probe beam. The measured electron density structure which is compared with a 2D PIC simulation, indicates that feasible condition can be generated 1.2 ns after the laser pulse. This electron density structure will be used for the laser wakefield acceleration experiments.
KERI, Changwon
Funding: Korea Electrotechnology Research Institute (KERI)
To generate the good quality electron bunch, stable fast injection is very important issue in the laser wakefield accelerator(LWFA). One of the self-injection methods is the wave breaking*. In this scheme, the density transition scale length is much larger than plasma skin depth. After a new self-injection mechanism using the sharp density transition scheme was proposed**, the experiment for the generation of the plasma shock structure have been conducted***. In this scheme, while one can reduce the wave breaking, the electron can be injected effectively using a phase mixing. Thus, the sharp density transition scheme is promising candidate method for the more stable generation of good quality electron bunch. In this scheme, the main issue is that the finding optimum conditions in which the injected electrons only in the first period of laser wake wave are accelerated further. In this paper, optimum conditions of sharp density transition scheme have been studied using Particle-In-Cell simulations. And the transverse parabolic profile is used to increase the beam quality. Throughout the extensive simulation work, the optimum conditions for the experiments at KERI is presented.
*S. Bulanov, et. al., Phys. Rev. E, 58, R5257 (1998)
**H. Suk, et. al., Phys. Rev. Lett. 86, {10}11 (2001)
***J. U. Kim, et. al., 69, 026409 (2004)
LBNL, Berkeley, California
Tech-X, Boulder, Colorado
Funding: Funded by the U.S. DOE Office of Science HEP including contract DE-AC02-05CH11231 and SciDAC, and by U.S. DOE NA-22, DARPA, and NSF
Collider and light source applications of laser wakefield accelerators will likely require staging of controlled injection with multi-GeV accelerator modules to produce and maintain the required low emittance and energy spread. We present simulations of upcoming 10 GeV-class LWFA stages, towards eventual collider modules for both electrons and positrons*. Laser and structure propagation are controlled through a combination of laser channeling and self guiding. Electron beam evolution is controlled through laser pulse and plasma density shaping, and beam loading. This can result in efficient stages which preserve high quality beams. We also present results on controlled injection of electrons into the structure to produce the required low emittance bunches using plasma density gradient** and colliding laser pulses. Tools for accurately modeling emittance and energy spread will be discussed***.
*E. Cormier-Michel et al., Proc. Adv Accel. Workshop 2008.
**C.G.R. Geddes et al., PRL 2008.
***E. Cormier-Michel et al, PRE 2008; C.G.R. Geddes et al, Proc. Adv Accel. Workshop 2008.
LBNL, Berkeley, California
University of Nevada, Reno, Reno, Nevada
Funding: Supported by the Office of High Energy Physics of the U.S. DOE under Contract No. DE-AC02-05CH11231, and DARPA.
Laser wakefield acceleration experiments were carried out by using various hydrogen-filled capillary discharge waveguides. Self-trapping of electrons showed strong correlation with the delay between the onset of the discharge current and arrival of the laser pulse (discharge delay). By de-tuning discharge delay from optimum guiding performance, self-trapping was found to be stabilized. Several possible scenarios for the enhanced trapping will be discussed along with spectroscopy of the transmitted laser light and the discharge recombination light.
LBNL, Berkeley, California
Funding: US Department of Energy
Staging Laser Plasma Accelerators (LPA), which is necessary in order to substantially increase the electron beam energy, requires incoupling additional laser beams into accelerating stages. To preserve high accelerating gradient of LPA, it is imperative to minimize the distance that is needed for laser incoupling. Using a conventional mirror with PW-class lasers will require the incoupling distance to be as long as tens of meters due to limitations imposed by laser induced damage of the optic. In this presentation we will describe a new approach for the laser incoupling that is based on planar water jet plasma mirror. The plasma mirror can operate as close as few cm to the focus of the laser thus minimizing the coupling distance. Using a water jet instead of a solid target avoids mechanical scanning of the target surface as well as contamination of the vacuum by laser breakdown debris. Experimental results showing performance of the water jet plasma mirror will be presented and progress in staging experiments will be discussed
LBNL, Berkeley, California
Funding: Supported by the Office of Science, Office of High Energy Physics, of the U.S. DOE under Contract No. DE-AC02-05CH11231.
Laser-driven plasma-based accelerators have made rapid progress in the last several years, yielding high-quality GeV electron beams accelerated over several centimeters.* Due to the ultra-high accelerating gradients, employing laser-plasma-accelerator technology has the potential to significantly reduce the linac length (and therefore cost) of a future lepton collider. The prospects and design considerations for a next-generation electron-positron linear collider based on laser-plasma accelerators are discussed. Staging of ultra-high gradient laser-plasma accelerating structures is examined, and plasma density scaling laws are derived for relevant collider parameters. Emittance growth via beam-plasma scattering is analyzed. An example of self-consistent parameters for a 1 TeV laser-plasma-based collider is presented.
*W.P. Leemans et al., ‘‘GeV electron beams from a centimetre-scale accelerator,'' Nature Physics 2, 696 (2006).
LLNL, Livermore, California
UCLA, Los Angeles, California
UCSD, La Jolla, California
Funding: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and DE-FG03-92ER40727, and LDRD 06-ERD-056
Recent laser wakefield acceleration experiments at the Jupiter Laser Facility, Lawrence Livermore National Laboratory, will be discussed where the Callisto Laser has been upgraded and has demonstrated 60 fs, 10 J laser pulses. This 150 TW facility is providing the foundation to develop a GeV electron beam and associated betatron x-ray source for use on the petawatt high-repetition rate laser facility currently under development at LLNL. Initial self-guided experiments have produced high energy monoenergetic electrons while experiments using a multi-centimeter long magnetically controlled optical plasma waveguide are investigated. Measurements of the electron energy gain and electron trapping threshold using 150 TW laser pulses will be presented.
MIT/PSFC, Cambridge, Massachusetts
Funding: This work was supported by the Department of Energy, Grant No. DE-FG02-95ER40919 and the Air Force Office of Scientific Research, Grant No. FA9550-06-1-0269.
Relativistic elliptic electron beams have applications in the research and development of a new class of elliptic- or sheet-beam klystrons which have the potential to outperform conventional klystrons in terms of power, efficiency, and operating voltage. This paper reports on results of a small-signal analysis of space-charge waves on a relativistic elliptic electron beam in a perfectly-conducting beam tunnel. A dispersion relation is derived. A computer code is developed and used in studies of the dispersion characteristics of various relativistic elliptic electron beams.
NSC/KIPT, Kharkov
Essential increase of wakefield intensity at excitation by a long train of relativistic electron bunches when the rectangular dielectric structure is filled with plasma was experimentally observed. A train of bunches was produced by the linear resonant accelerator. Parameters of the beam: energy 4.5 MeV, pulsed current 0.5 A, pulse duration 2 mksec. Such macro-pulse consists of a periodic sequence of 6000 electron bunches. Each electron bunch has duration 60 psec, diameter 1.0 cm, angular spread 0.05 mrad, charge 0.16 nC. Bunches repetition frequency is 2805 MHz. Transit channel for bunches is filled with gas at various pressure. The first portion of the bunches ionizes gas so that plasma frequency is equal to bunch repetition frequency and to the frequency of principal eigen mode of the dielectric structure. Excitation enhancement at such resonant conditions is being studied taking into account the improvement of bunch train propagation in the transit channel and electrodynamics change of the dielectric structure at filling with plasma.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
USC, Los Angeles, California
Funding: Work supported in part by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
An electron beam driven Plasma Wake-Field Accelerator (PWFA) has recently sustained accelerating gradients above 50GeV/m for almost a meter. Future experiments will transition from using a single bunch to both drive and sample the wakefield, to a two bunch configuration that will accelerate a discrete bunch of particles with a narrow energy spread and preserved emittance. The plasma works as an energy transformer to transform high-current, low-energy bunches into relatively lower-current higher-energy bunches. This method is expected to provide high energy transfer efficiency (from 30% up to 95%) from the drive bunch to the accelerated witness bunch. The PWFA has a wide variety of applications and also has the potential to greatly lower the cost of future accelerators. We discuss various possible uses of this technique such as: linac based light sources, injector systems for ring based synchrotron light sources, and for generation of electron beams for high energy electron-hadron colliders.
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
Plasma Wake Field Accelerator (PWFA) has a very attractive accelerating gradient which can be three orders of magnitude higher than that of the traditional accelerator. In this paper the positron acceleration in a particle beam driven PWFA is studied both in the linear and weakly nonlinear region by using Particle In Cell (PIC) simulation. A preliminary parameters design is obtained for such acceleration scheme.
UCLA, Los Angeles, California
SLAC, Menlo Park, California
Duke University, Durham, North Carolina
USC, Los Angeles, California
Funding: Work supported by DOE under contracts DE-FG03-92ER40727, DE-FG52-06NA26195, DE-FC02-07ER41500, DE-FG02-03ER54721.
Recent Plasma Wake-Field Acceleration (PWFA) experiments at Stanford Linear Accelerator Center has demonstrated electron acceleration from 42GeV to 84GeV in less than one meter long plasma section. The accelerating gradient is above 50GeV/m, which is three orders of magnitude higher than those in current state-of-art RF linac. Further experiments are also planned with the goal of achieving acceleration of a witness bunch with high efficiency and good quality. Such PWFA sections with 25 GeV energy gain will be the building blocks for a staged TeV electron-positron linear collider concept based on PWFA (PWFA-LC). We conduct Particle-In-Cell simulations of these PWFA sections at both the initial and final witness beam energies. Different design options, such as Gaussian and shaped bunch profiles, self-ionized and pre-ionized plasmas, optimal bunch separation and plasma density are explored. Theoretical analysis of the beam-loading* in the blow-out regime of PWFA and simulation results show that highly efficient PWFA stages are possible. The simulation needs, code developments and preliminary simulation results for future collider parameters will be discussed.
*M. Tzoufras et al, Phys. Rev. Lett. {10}1, 145002 (2008).
UCLA, Los Angeles, California
SLAC, Menlo Park, California
Funding: Work supported by DOE grant numbers: DE-FG03-92ER40727, DE-FG52-06NA26195, DE-FC02-07ER41500, DE-FG02-03ER54721
The fourth generation of light sources (such as LCLS and the XFEL) require high energy electron drivers (16-20GeV) of very high quality. We are exploring the possibility of using a high transformer ratio PWFA to meet these challenging requirements. This may have the potential to reduce the size of the electron drivers by a factor of 5 or more, therefore making these light source much smaller and more affordable. In our design, a high charge (5-10nC) low energy driver (1-3GeV) with an elongated current profile is used to drive a plasma wake in the blowout regime with a high transformer ratio (5 or more). A second ultra-short beam that has high quality and low charge beam (1nC) can be loaded into the wake at a proper phase and be accelerated to high energy (5-15GeV) in very short distances (10s of cms). The parameters can be optimized, such that high quality (0.1% energy spread and 1mm mrad normalized emittance) and high efficiency (60-80%) can be simultaneously achieved. The major obstacle for achieving the above goals is the electron hosing instabilities in the blowout regime. In this poster, we will use both theoretical analysis and PIC simulations to study this concept.
UCLA, Los Angeles, California
Instituto Superior Tecnico, Lisbon
Funding: Work Supported by DOE Grant DEFG02-92ER40727
Controlling the trapping of electrons into accelerating wakefields is an important step to obtaining a stable reproducible electron beam from a laser wakefield accelerator (LWFA). Recent experiments at UCLA have focused on using the different ionization potentials of gases as a mechanism for controlling the trapping of electrons into an LWFA. The accelerating wakefield was produced using an ultra-intense (Io ~ 1019 W / cm2 ), ultra-short (τFWHM ~ 40 fs) laser pulses. The laser pulse was focused onto the edge of column of gas created by a gas jet. The gas was a mixture of helium and nitrogen. The rising edge of the laser pulse fully ionizes the helium and the first five bound electrons of the nitrogen. Only at the peak of the laser pulse is it intense enough to ionize the most tightly bound electrons of the nitrogen. Electrons which are ionized at the peak of laser pulse are born into a favorable phase space within the accelerating wakefield and are subsequently trapped and accelerated. The accelerated electrons were dispersed using a dipole magnet with a ~ 1 Tesla magnetic field onto a phosphor screen. Electron beam energy spectrum charge and divergence were measured.
UCLA, Los Angeles, California
Funding: This work was supported by The Department of Energy Grant No.DEFG02-92ER40727.
The self-guiding of relativistically intense but ultra-short laser pulses has been experimentally investigated as a function of laser power, plasma density and plasma length in the so-called "blowout" regime. Although etching of the short laser pulse due to diffraction and local pump depletion erodes the the head of the laser pulse, an intense portion of the pulse is guided over tens of Rayleigh lengths, as observed by imaging the exit of the plasma. Spectrally-resolved images of the laser pulse at the exit of the plasma show evidence for photon acceleration as well as deceleration (pump depletion)in a well defined narrow guided region. This is indicative of the self-guided pulse residing in the wake excited in the plasma. Energy outside the guided region was found to be minimized when the initial conditions at the plasma entrance were closest to the theoretical matching conditions for guiding in the blowout regime. The maximum extent of the guided length is shown to be consistent with the nonlinear pump depletion length predicted by theory.
UCSD, La Jolla, California
UCLA, Los Angeles, California
LLNL, Livermore, California
We present experimental results showing the formation of a laser produced optical waveguide, suitable for laser guiding, when applying a high external magnetic field around a gas cell. This technique is directly applicable to wakefield acceleration and has been established at the Jupiter Laser Facility; an external magnetic field prevents radial heat transport, resulting in an increased electron temperature gradient [D. H. Froula et.al., Plasma Phys. Control. Fusion, 51, 024009 (2009)]. Interferometry and spatially resolved Thomson-scattering diagnostics measure the radial electron density profile, and show that multiple-centimeter long waveguides with minimum electron densities of 1017 to 1018 cm-3 can be produced. Temporally resolved Thomson-scattering is also performed to characterize the evolution of the density channel in time. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was partially funded by the Laboratory Directed Research and Development Program under project tracking code 06-ERD-056.
USTRAT/SUPA, Glasgow
Instituto Superior Tecnico, Lisbon
University of Oxford, Oxford
STFC/RAL, Chilton, Didcot, Oxon
University of Oxford, Clarendon Laboratory, Oxford
University of Glasgow, Glasgow
Funding: EPSRC and EU Euroleap
Advances in laser-plasma wake field accelerators (LWFA) have now reached the point where they can be considered as drivers of compact radiation sources covering an large spectral range. We present recent results from the Advanced Laser Plasma High-energy Accelerators towards X-rays (ALPHA-X) project. These include the first ultra-compact gamma ray source producing brilliant 10fs pulses of x-ray photons > 150keV. We present new opportunities for harnessing laser-driven plasma waves to accelerate electrons to high energies and use these as a basis for ultra-compact radiation sources with unprecedented peak brilliance and pulse duration. We have demonstrated a brilliant tabletop gamma ray source based on enhanced betatron emission in a plasma channel which produces > 109 photons per pulse in a bandwidth of 10-20%. We present results of a compact synchrotron source based on a LWFA and undulator and discuss the potential of developing an FEL based this technology. Finally we discuss the plans for the Scottish Centre for the Application of Plasma-based Accelerator (SCAPA), which is being set up to develop and apply compact radiation sources, laser-driven ion sources and LWFAs.
QMUL, London
USC, Los Angeles, California
For 70 years particle acceleration schemes have been based on the same technology which places particles onto rf electric fields inside metallic cavities. However, since the accelerating gradients cannot be increased arbitrarily due to limiting effects such as wall breakdown, in order to reach higher energies today’s accelerators require km-long structures that have become very expensive to build, and therefore novel accelerating techniques are needed to push the energy frontier further. Plasmas do not suffer from those limitations since they are gases that are already broken down into electrons and ions. In addition, the collective behavior of the particles in plasmas allows for generated accelerating electric fields that are orders of magnitude larger than those available in conventional accelerators. As plasma acceleration technologies mature, one of the main future challenges is to monoenergetically accelerate a second trailing bunch by multiplying its energy in an efficient manner, so that it can potentially be used in a future particle collider. The work presented here analyzes the use of multiple electron bunches in order to enhance certain plasma acceleration schemes.
PPPL, Princeton, New Jersey
LLNL, Livermore, California
LBNL, Berkeley, California
Voss Scientific, Albuquerque, New Mexico
Funding: Research supported by the US Department of Energy.
Neutralized drift compression offers an effective means for particle beam focusing and current amplification. In neutralized drift compression, a linear radial and longitudinal velocity drift is applied to a beam pulse, so that the beam pulse compresses as it drifts in the focusing section. The beam intensity can increase more than a factor of 100 in both the radial and longitudinal directions, totaling to more than a 10,000 times increase in the beam density during this process. The optimal configuration of focusing elements to mitigate the time-dependent focal plane is discussed in this paper. The self-electric and self-magnetic fields can prevent tight ballistic focusing and have to be neutralized by supplying neutralizing electrons. This paper presents a survey of the present numerical modeling techniques and theoretical understanding of plasma neutralization of intense particle beams. Investigations of intense beam pulse interaction with a background plasma have identified the operating regimes for stable and neutralized propagation of intense charged particle beams.
LBNL, Berkeley, California
LLNL, Livermore, California
PPPL, Princeton, New Jersey
Voss Scientific, Albuquerque, New Mexico
The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the warm dense matter regime, using space-charge-dominated ion beams that are simultaneously longitudinally bunched and transversely focused. Longitudinal beam compression by large factors has been demonstrated in the Neutralized Drift Compression Experiment (NDCX) with controlled ramps and forced neutralization. Using an injected 30 mA K+ ion beam with initial kinetic energy 0.3 MeV, axial compression leading to ~100X current amplification and simultaneous radial focusing to a few mm have led to encouraging energy deposition approaching the intensities required for eV-range target heating experiments. We discuss the status of several improvements to NDCX to reach the necessary higher beam intensities, including:
- greater axial compression via a longer velocity ramp;
- beam steering dipoles to mitigate aberrations in the bunching module;
- time-dependent focusing elements to correct considerable chromatic aberrations; and
- plasma injection improvements to establish a plasma density always greater than the beam density, expected to be >1013 cm-3.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
Funding: Work supported by U.S. DoE Grant No. DE-FG03-92ER40693.
The first successful attempt to generate ultrashort (1-10 picosecond) relativistic electron bunches characterized by a ramped current profile that rises linearly from head to tail and then falls sharply to zero was recently reported.* Bunches with this type of longitudinal shape may be applied to plasma-based accelerator schemes as an optimized drive beam, and to free electron lasers as a means of reducing asymmetry in microbunching due to slippage. We will review the technique used to generate these bunches, which utilizes a sextupole-corrected dogleg compressor to manipulate the longitudinal phase space of the beam, and examine its potential application in a realistic plasma wakefield accelerator scenario, the proposed FACET project at SLAC.
* R. J. England, J. B. Rosenzweig, G. Travish, Phys. Rev. Lett. 100, 214802 (2008).
BNL, Upton, Long Island, New York
UCLA, Los Angeles, California
Trains of subpicosecond electron bunches are essential to reach high transformer ratio and high efficiency in compact, beam-driven, plasma-based accelerators. These trains with a correlated energy chirp can also be used in pump-probe experiments driven by FELs. We demonstrate experimentally for the first time that such trains with controllable bunch-to-bunch spacing, bunch length, and charge can be produced using a mask technique. With this simple mask technique, the stability of the bunch train in energy and time is guaranteed by the beam feedback system.
USC, Los Angeles, California
Funding: Work supported by US Department of Energy
Preservation of the incoming beam emittance is a key characteristic needed for any accelerating system, including the beam-driven, plasma-based accelerator or plasma wakefield accelerator (PWFA). Electron beams with a density larger than the plasma density propagate in a pure and uniform plasma ion column that acts as a focusing element free of geometric aberrations, and the beam emittance is preserved. On the contrary, positron beams attract plasma electrons that flow through the beam and create a non-uniform charge density inside the beam that can exceed the beam density. The resulting plasma focusing force is non-uniform and non-linear. Experimentally, we observe the formation of a beam halo on a screen placed downstream from the plasma. Analysis of the beam images as a function of the plasma density show that the transverse beam size at the screen is strongly reduced in the high emittance plane, and that in the low emittance plane charge is transferred from the beam core to the halo. Numerical simulations of the experiments show the same behavior and indicate that there is emittance growth is both planes. Experimental and simulations will be presented.
UNL, Lincoln
Funding: Air Force Office of Scientific Research, Defense Advanced Research Projects Agency, Domestic Nuclear Detection Office, Department of Homeland Security
High-power, ultrashort laser pulses have been shown to generate quasi-monoenergetic electron beams from underdense plasmas. Several groups have reported generating high-energy electron beams using either supersonic nozzles* or a capillary based system**. Many issues still remain, with respect to pointing and energy stability of the beam, charge in the monoenergetic component, energy spread, and robustness. We demonstrate for the first time the generation of 300-400 MeV electron beams with 600 pC of charge, using self-guided laser pulses and a stable, high-quality laser pulse. Matching the laser to the plasma is crucial for stable operation since there is minimal nonlinear evolution of the pulse. The beam is highly reproducible in terms of pointing stability and energy with parameters superior to those previously obtained using optical injection***. The stability and compactness of this accelerator make it possible to conceive of mobile applications in non-destructive testing, or long-standoff detection of shielded special nuclear materials. Scaling laws indicate that with a longer plasma and higher laser powers it should be possible to obtain stable, GeV class electron beams.
* S.P.D. Mangles et al., Nature 431, 535-538 (2004.
** W.P. Leemans et al., Nature Physics 2, 696-699 (2006).
*** J. Faure et al., Nature 444, 737-739 (2007).
LBNL, Berkeley, California
Funding: Funded by the U.S. DOE Office of Science HEP including contract DE-AC02-05CH11231, and by DARPA.
A key issue in laser wakefield accelerators (LWFAs) is injection of electrons into the accelerating region of the wake. Typically electron beams have been self-injected into the wake in a highly non-linear process, and at a higher plasma density than that for an optimized guiding and accelerating structure. This in turn limits the electron beam energy and quality that can be achieved. In this talk it is shown that this coupling of injection and acceleration can be addressed for LWFA in a capillary discharge waveguide with the use of a gas jet embedded into the capillary to longitudinally tailor the electron density profile. Previous experiments without a gas jet have shown self-trapping and acceleration of electrons with energy up to 1 GeV [Leemans et al., Nature Phys. Vol. 2, 696, 2006]. By adding a gas jet in the capillary it has been shown that electrons can be trapped and accelerated to high-energy using plasma densities in the capillary lower than in previous experiments, and that use of this technique improved electron beam properties.
USTRAT/SUPA, Glasgow
University of Dundee, Nethergate, Dundee, Scotland
UAD, Dundee
Funding: The U.K. EPSRC and the European Community - New and Emerging Science and Technology Activity under the FP6 “Structuring the European Research Area” programme (project EuroLEAP, contract number 028514)
The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) programme* is developing laser-plasma accelerators for the production of ultra-short electron beams as drivers of incoherent and coherent radiation sources from plasma and magnetic undulators**. Initial quantitative measurements of the electron beam properties have been made. A high power (20 TW) femtosecond laser pulse is focused into a gas jet (length 2 mm) and electrons from the laser-induced plasma are self-injected into the accelerating potential of the plasma density wake behind the laser pulse. The electron beam pointing as it exits the gas jet is as large as 10 mrad. Understanding the pointing stability is an essential step for reproducible beam transport and we present a theoretical model to account for this behaviour. The beam divergence is as low as 2 mrad, which is consistent with a normalised emittance of the order of 1 pi mm mrad. The maximum central energy of the beam is ~90 MeV with r.m.s. relative energy spread as low as 0.8%. An analysis of this unexpectedly high beam quality is presented and its impact on the viability of a free-electron laser*** driven by such a beam is examined.
* D. A. Jaroszynski et al., Phil. Trans. R. Soc. A 364, 689 (2006).
** H.-P. Schlenvoigt et al., Nature Phys. 4, 130 (2008).
*** B. Shepherd and J. Clarke, Proc. EPAC 2006, 3580 (2006).
Instituto Superior Tecnico, Lisbon
UCLA, Los Angeles, California
Funding: F.C.Gulbenkian, F.C.T. [SFRH/BD/35749/2007, PTDC/FIS/66823/2006 (Portugal)], and European Community - New and Emerging Science and Technology Activity, FP6 program (project EuroLeap, contract #028514)
We address full particle-in-cell simulations of the next generation of Laser Wakefield Accelerators with energy gains > 10 GeV. The distances involved in these numerical experiments are very demanding in terms of computational resources and are not yet possible to (easily) accomplish. Following the work on simulations of particle beam-plasma interaction scenarios in optimized Lorentz frames by J.-L. Vay*, the Lorentz transformation for a boosted frame was implemented in OSIRIS**, leading to a dramatic change in the computational resources required to model LWFA. The critical implementation details will be presented, and the main difficulties discussed. Quantitative comparisons between lab/boost frame results with OSIRIS, QuickPIC***, and experiment will be given. Finally, the results of a three-dimensional PIC simulation of a > 10 GeV accelerator stage will be presented, including a discussion on radiation emission.
* J.-L. Vay, PRL 98, 130405 (2007)
** R.A. Fonseca et al., LNCS 2329, III-342 (Springer-Verlag, 2002)
*** C. Huang, et al., JCP 217, Issue 2, 20 (2006)
Fermilab, Batavia
Tech-X, Boulder, Colorado
Simulation of the microwave transmission properties through the electron cloud at the Fermilab Main Injector have been implemented using the plasma simulation code ‘‘VORPAL". Phase shifts and attenuation curves have been calculated for the lowest frequency TE mode, slightly above the cutoff frequency, in field free regions, in the dipoles and quadrupoles. Preliminary comparisons with experimental results are discussed and will guide the next generation of experiments.
ANL, Argonne
Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357.
Kinetic space plasma simulations are dominated by PIC (Particle-In-Cell) codes. Due to the inherent noise in PIC simulations, interest in directly solving the Vlasov equation is increasing. With the fast development of supercomputers, this is becoming more realistic. We present our preliminary work on solving the Vlasov equation for beam dynamics simulations*. A high order Spectral Element Method has been applied to achieve high accuracy, easy interpolation, and parallelization. Due to the inherent instability of the Vlasov equation, a spectral filter has been added and mass conservation has been satisfied. The proposed algorithms were validated on 1D1V simulations. A paraxial model of the Vlasov equation (2D2V) has also been studied and compared with PIC simulations at ANL using the BG/P supercomputer.
*J. Xu, P. Ostroumov and J. Nolen, “Highly Scalable Parallel Algorithm for 2D2V Vlasov Equation with High Order Spectral Element Method”, poster on SC08, Austin, Texas, Nov.15-20, 2008.
Far-Tech, Inc., San Diego, California
ANL, Argonne
Funding: This work is supported by the US DOE SBIR program
GEM, developed by FAR-TECH Inc, is a self consistent hybrid code to simulate general ECRIS plasma. It calculates EDF (electron distribution function) using a bounce-averaged Fokker-Planck code and calculates the ion flow using a fluid code, which has been modified to implement new boundary settings including fixed boundary ion velocities or fixed sheath potentials at both ends of the device. Extensive studies on the convergence and performance of the code have been performed. Also, GEM has been connected to MCBC (Monte Carlo beam capture) code and the validations of the code using ANL ECR-I charge breeding data and other published experiments are underway. The typical converged solutions of GEM and the comparisons with the experiments will be presented and discussed.
LBNL, Berkeley, California
LLNL, Livermore, California
Funding: Supported by the US-DOE under Contracts DE-AC02-05CH11231 and DE-AC52-07NA27344, and a DOD SBIR Phase II. Used resources of NERSC, supported by the US-DOE under Contract DE-AC02-05CH11231.
The development of advanced accelerators often involves the modeling of systems that involve a wide range of scales in space and/or time, which can render such modeling extremely challenging. The Adaptive Mesh Refinement technique can be used to significantly reduce the requirements for computer memory and the number of operations. Its application to the fully self-consistent modeling of beams and plasmas is especially challenging, due to properties of the Vlasov-Maxwell system of equations. Most recently, we have begun to explore the application of AMR to the modeling of laser plasma wakefield accelerators (LWFA). For the simulation of a 10GeV LWFA stage, the wake wavelength is O[100μm] while the electron bunch and laser wavelength are typically submicron in size. As a result, the resolution required for different parts of the problem may vary by more than two orders of magnitude in each direction, corresponding to up to 6 orders of magnitude of possible (theoretical) savings by use of mesh refinement. We present a summary of the main issues and their mitigations, as well as examples of application in the context of LWFA and similar beam-plasma interaction setup.
ORNL, Oak Ridge, Tennessee
Funding: *SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
The new SNS Allison emittance scanner measures emittances of 65 kV ion beams over a range of ± 116 mrad. Its versatile control system allows for time-dependent emittance measurements synchronized by an external trigger, and therefore is suited for studying pulsed systems. After a programmable delay the system acquires a variable array of beam current measurements, each averaged over a changeable time span. The baseline of the current measurements are determined by averaging a fraction of 1 ms shortly before the start of the ion beam pulse. This paper presents the time evolution of emittance ellipses during the 1 ms H- beam pulses emerging from the SNS test LEBT, which is important for loss considerations. In addition it presents the time evolution of emittance ellipses during the 3 week active lifetime of an SNS H- source, which is an operational issue. Additional emittance data characterize the dependence on the electron-dump voltage, the extractor voltage, and the LEBT lens voltages, all of which were critical for reaching the 38 mA baseline H- beam current. Emittance data for the dependence on the beam current highlight the challenges for the SNS power upgrade.
Saint-Petersburg State University, Saint-Petersburg
ANL, Argonne
Euclid TechLabs, LLC, Solon, Ohio
Funding: SBIR DOE (DE-FG02-08ER85031); Russian Foundation for Basic Research (06-02-16442-a); Physical Faculty of St.Petersburg State University (Russia) (14.10.08)
We consider microwave Cherenkov radiation in a waveguide containing an engineered medium, and show that the properties of the radiation can be used to determine the energy of charged particle beams. These properties can form the basis of a new technique for bunch diagnostics in accelerators. We propose to use a material characterized by a diagonal permittivity tensor with components depending on frequency as in the case of a plasma but with the constant terms not equal to unity. These properties can be realized in a metamaterial with a relatively simple structure. In contrast to previous work in the present paper a vacuum channel in the waveguide is taken into account. The particle energy can be determined by measurement of mode frequencies. It is shown that a strong dependence of mode frequencies on particle energy for some predetermined narrow range can be obtained by appropriate choice of the metamaterial parameters and radius of the channel. It is also possible to obtain energy measurements over a wider range at the cost of a weaker frequency dependence.
*A.V.Tyukhtin, S.P.Antipov, A.Kanareykin, P.Schoessow, PAC07, p.4156.
**A.V.Tyukhtin, EPAC08, p.1302.
***A.V.Tyukhtin, Technical Physics Letters, v.34, p.884 (2008); v.35 (2009), in press.
Fermilab, Batavia
PPPL, Princeton, New Jersey
Funding: Research supported by the U.S. Department of Energy.
Understanding the effects of random errors in machine components such as quadrupole magnets and RF cavities is essential for the optimum design and stable operation of high-intensity accelerators. The effects of random errors have been studied theoretically, but systematic experimental studies have been somewhat limited due to the lack of dedicated experimental facilities. In this paper, based on the compelling physics analogy between intense beam propagation through a periodic focusing quadrupole magnet system and pure ion plasma confined in a linear Paul trap, experimental studies of random error effects have been performed using the Paul Trap Simulator Experiment (PTSX). It is shown that random errors in the quadrupole focusing strength continuously produce a non-thermal tail of trapped ions, and increases the rms radius and the transverse emittance almost linearly with the amplitude and duration of the noise. This result is consistent with 2D WARP PIC simulations. In particular, it is observed that random error effect can be further enhanced in the presence of beam mismatch.
MIT/PSFC, Cambridge, Massachusetts
Funding: This work was supported by the Department of Energy, Grant No. DE-FG02-95ER40919 and the Air Force Office of Scientific Research, Grant No. FA9550-06-1-0269.
An adiabatic warm-fluid equilibrium theory for a thermal charged-particle beam in an alternating gradient (AG) focusing field is presented. Warm-fluid equilibrium equations are solved in the paraxial approximation and the rms beam envelope equations and the self-consistent Poisson equation, governing the beam density and potential distributions, are derived. The theory predicts that the 4D rms thermal emittance of the beam is conserved, but the 2D rms thermal emittances are not constant. Although the presented rms beam envelope equations have the same form as the previously known rms beam envelope equations, the evolution of the rms emittances in the present theory is given by analytical expressions. The beam density is calculated numerically, and it does not have the simplest elliptical symmetry, but the constant density contours are ellipses whose aspect ratio decreases as the density decreases along the transverse displacement from the beam axis. For high-intensity beams, the beam density profile is flat in the center of the beam and falls off rapidly within a few Debye lengths, and the rate at which the density falls is approximately isotropic in the transverse directions.
Nagaoka University of Technology, Nagaoka, Niigata
TIT, Yokohama
Possible emittance growth due to a nonuniform particle distribution can be analyzed with a thermal equilibrium state in various space-charge potential beams. The possible emittance growth is given by a function of a space-charge tune depression and a nonlinear field energy factor. The nonlinear field energy factor, which is determined by nonuniformity of a charge distribution, is estimated in the thermal equilibrium distribution on a cross-section in a beam. The nonlinear field energy factor changes with space-charge potential for the thermal equilibrium distribution. It is expected that the possible emittance growth will be decreased effectively to consider in the thermal equilibrium condition.
PPPL, Princeton, New Jersey
Funding: Research supported by the U. S. Department of Energy.
The transverse dynamics of an intense charged particle beam propagating through a periodic quadrupole focusing lattice is described by the nonlinear Vlasov-Maxwell system of equations where the propagating distance plays the role of time. To find matched-beam quasi-equilibrium distribution functions one need to determine a dynamical invariant for the beam particle moving in the combined external and self-fields. The standard approach for sufficiently small phase advance is to use the smooth focusing approximation, where particle dynamics is determined iteratively using the small parameter (vacuum phase advance)/(360 degrees) < 1 accurate to cubic order. In this paper, we present a perturbative Hamiltonian transformation method which is used to transform away the fast particle oscillations and obtain the average Hamiltonian accurate to 5th order in the expansion parameter. This average Hamiltonian, expressed in the original phase-space variables, is an approximate invariant of the original system, and can be used to determine self-consistent beam equilibria that are matched to the focusing channel.
IF-UFRGS, Porto Alegre
Funding: CNPq, Brazil; AFOSR FA9550-06-1-0345, USA
In this work we analyze the dynamics of mismatched inhomogeneous beams of charged particles. Initial inhomogeneities lead to propagating density waves across the beam core, and the presence of density waves eventually results in density build up and particle scattering. Particle scattering off waves in the beam core and the presence of resonances due to envelope mismatches ultimately generate a halo of particles with concomitant emittance growth. Emittance growth directly indicates when the beam relaxes to its final stationary state, and the purpose of the present paper is to describe halo and emittance in terms of test particles moving under the action of the mismatched inhomogeneous beam. To this end we develop an average Lagrangian approach for the beam where both density and envelope mismatches are incorporated. Test particle results compare well with full simulations.
PPRC, Tehran
IPM, Tehran
2D potential profiles for uniformly populated discs of charged particles with circular and elliptical cross sections inside a perfectly conducting ring are simulated using the method of images. The results are compared with the problem of infinitely long linear charge distribution inside a conducting cylinder with a dependence only on the two transverse coordinates*.
*Miguel A. Furman Phys. Rev. ST Accel. Beam 10, 081001(2007)
Tech-X, Boulder, Colorado
Funding: This project was in part supported by DOE Office of Advanced Scientific Computing Research SBIR Phase II grant #DE-FG02-07ER84731, SciDAC Grant #DE-FC02-07ER41499, and Tech-X Corporation.
In order to meet the design and budget constraints of next generation particle accelerators, individual components have to be optimized using numerical simulations. Among the optimizations are the geometric shape of RF cavities and the placement of coupler and dampers, requiring large numbers of simulations. It is therefore desirable to accelerate individual cavity simulations. Finite-Difference Time-Domain (FDTD) is a widely used algorithm for modeling electromagnetic fields. While being a time-domain algorithm, it can also be used to determine cavity modes and their frequencies. Weak scaling of parallel FDTD yields good results due to the algorithm locality, but the maximum speedup is determined by the usually small problem size. Graphics Processing Units (GPUs) offer a huge amount of processing power and memory bandwidth, well suited for accelerating FDTD simulations. We therefore developed an FDTD solver on GPUs and incorporated it into the plasma simulation code VORPAL. We will present GPU accelerated VORPAL simulations, provide speedup figures and address the effect of running these simulations in single precision.
Tech-X, Boulder, Colorado
JLAB, Newport News, Virginia
Funding: Department of Energy SBIR grant DE-FG02-05ER84172
We will present the results of benchmarking simulations run to test the ability of VORPAL to model multipacting processes in Superconducting Radio Frequency structures. VORPAL is an electromagnetic (FDTD) particle-in-cell simulation code originally developed for applications in plasma and beam physics. The addition of conformal boundaries and algorithms for secondary electron emission allow VORPAL to be applied to multipacting processes. We start with simulations of multipacting between parallel plates where there are well understood theoretical predictions for the frequency bands where multipacting is expected to occur. We reproduce the predicted multipacting bands and demonstrate departures from the theoretical predictions when a more sophisticated model of secondary emission is used. Simulations of existing cavity structures developed at Jefferson National Laboratories will also be presented where we compare results from VORPAL to experimental data.
Tech-X, Boulder, Colorado
LBNL, Berkeley, California
FZK, Karlsruhe
Funding: This work funded by the Department of Energy under Small Business Innovation Research Contract No. DE-FG02-08ER85042.
Microwave transmission in accelerator beam pipes is providing a unique method for determining electron cloud characteristics, such as density, plasma temperature, and potentially the efficacy of electron cloud mitigation techniques. Physically-based numerical modeling is currently providing a way to interpret the experimental data, and understand the plasma-induced effects on rf signals. We report here recent applications of numerical simulation of microwave transmission in the presence of electron clouds. We examine the differences in phase shift induced by TE11 and TM01 modes in circular cross section beam pipes for uniform density electron clouds. We also detail numerical simulation of the cyclotron resonance and examine how the width of the resonance changes with applied dipole magnetic fields strength and cloud temperature.
CERN, Geneva
MPI-P, München
Short high-energy proton bunches have been proposed as efficient drivers for future single-stage electron-beam plasma accelerators. We discuss if and how the desired proton bunches could be obtained in the CERN accelerator complex, considering various compression schemes, such as a fast non-adiabatic lattice change prior to extraction from a storage ring or the use of transversely deflecting cavities.
LBNL, Berkeley, California
Funding: This work supported by DARPA and US DoE Office of High Energy Physics under contract DE-AC02-05CH11231.
Ultrashort terahertz pulses with energies in the μJ range can be generated with laser wakefield accelerators (LWFA), which produce ultrashort electron bunches with energies up to 1 GeV* and energy spreads of a few-percent. At the plasma-vacuum interface these ultrashort bunches emit coherent transition radiation (CTR) in a wide bandwidth (~ 1 - 10 THz) yielding terahertz pulses of high intensity**,***. In addition to providing a non-invasive bunch-length diagnostic**** and thus feedback for the LWFA, these high peak power THz pulses are suitable for high field (MV/cm) pump-probe experiments. Maximizing the radiated energy was done by controlling the THz mode quality and by optimizing both the energy and the charge of the electron bunches via pre-pulse control on the driver beam. Here we present the study of three different techniques for pre-pulse control and we demonstrate the production of μJ-class THz pulses using energy-based and single-shot electro-optic measurements.
*W.P. Leemans et al., Nature Physics 2, 696 (2006)
**W.P. Leemans et al., PRL 91, 074802 (2003)
***C.B. Schroeder et al., PRE 69, 016501 (2004)
**** J. van Tilborg et al., PRL 96, 014801 (2006)
MPI-P, München
BINP SB RAS, Novosibirsk
HHUD, Dusseldorf
The idea of proton bunch driven plasma wakefield acceleration was recently proposed. The motivation is to use an existing high energy proton beam to drive a large amplitude accelerating electric field, and then accelerate the electrons to the energy frontier. Simulations of the plasma wakefield production and acceleration process from a PIC code are given in this paper. In order to get high accelerating field, the required proton bunch length is extremely small. The preliminary design parameters for bunch compression are also presented.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
High gradient acceleration of electrons has recently been achieved in meter scale plasmas at SLAC. Results from these experiments show that the wakefield is sensitive to parameters in the electron beam which drives it. In the experiment the bunch lengths were varied systematically at constant charge. Here we investigate the correlation of peak beam current to the wake amplitude. The effect of beam head erosion will be discussed and an experimental limit on the transformer ratio set. The results are compared to simulation.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
The effect of ion motion and the need for practical positron propagation in a plasma wakefield accelerator (PWFA) have incited interest in hollow plasma channels. These channels are typically assumed to be cylindrically symmetric; however, a different geometry might be easier to achieve. The introduction of an obstruction into the outlet of a high Mach number gas jet can produce two parallel slabs of gas separated by a density depression. Here, there is a detailed simulation study of the density depression created in such a system. This investigation reveals that the density depression is insufficient at the desired plasma density. However, insights from the simulations suggest another avenue for the creation of the hollow slab geometry.
Tech-X, Boulder, Colorado
LBNL, Berkeley, California
Funding: Work supported by Department of Energy contracts DE-AC02-05CH11231 (LBNL), DE-FC02-07ER41499 (SciDAC), and DE-FG02-04ER84097 (SBIR).
Simulation of laser wakefield accelerator (LWFA) experiments is computationally highly intensive due to the disparate length scales involved. Current experiments extend hundreds of laser wavelengths transversely and many thousands in the propagation direction, making explicit PIC simulations enormously expensive. We can substantially improve the performance of LWFA simulations by modeling the envelope modulation of the laser field rather than the field itself. This allows for much coarser grids, since we need only resolve the plasma wavelength and not the laser wavelength, and this also allows larger timesteps. Thus an envelope model can result in savings of several orders of magnitude in computational resources. By propagating the laser envelope in a Galilean frame moving at the speed of light, dispersive errors can be avoided and simulations over long distances become possible. Here we describe the model and its implementation. We show rigorous studies of convergence and discretization error, as well as benchmarks against explicit PIC. We also demonstrate efficient, fully 3D simulations of downramp injection and meter-scale acceleration stages.
IF-UFRGS, Porto Alegre
Funding: This work has received financial support from AFOSR, Arlington, VA (under Grant FA9550-06-1-0345) and from CNPq, Brazil.
In the present analysis we study the self consistent propagation of intense laser pulses in a cold relativistic ideal-fluid underdense plasma, with particular interest in how the envelope dynamics is affected by the plasma frequency. Analysis of the linear system associated with the chosen model shows the existence of thresholds that can led propagating pulses to distinct modulational instabilities, according to the relation between its transversal wave vector and the plasma frequency.
UCLA, Los Angeles, California
Funding: This work is supported by the DOE Contract No. DE-FG03-92ER40727.
Over the last several years, the Target Normal Sheath Acceleration (TNSA) mechanism in solid density plasmas produced by a laser pulse has achieved proton energies up to 10’s of MeV and quasi-monoenergetic beams at lower energies. Although solid-target experiments have demonstrated high-charge and low-emittance proton beams, little work has been done with gaseous targets which in principle can be operated at a very high repetition frequency. At the Neptune Laboratory, there is an ongoing experiment on CO2 laser driven proton acceleration using a rectangular (0.5x2mm) H2 gas jet as a target. The main goal is to study the coupling of the laser pulse into a plasma with a well defined density in the range of 0.5 to 2 times critical density and characterize the corresponding spectra of accelerated protons. Towards this end, the Neptune TW CO2 laser system is being upgraded to produce shorter 1-3ps pulses. These high-power pulses will allow us to investigate acceleration of protons via the TNSA and Direct Ponderomotive Pressure mechanisms as well as their combination. The current status of the proton source experiment will be presented.
UCLA, Los Angeles, California
USC, Los Angeles, California
BNL, Upton, Long Island, New York
Funding: Work supported by US Department of Energy.
One of the challenges for plasma wakefield accelerators (PWFAs) is to accelerate a trailing bunch with a narrow energy spread. The real challenge is to produce a bunch train with a least one drive bunch and one trailing bunch. We have demonstrated experimentally at the BNL-ATF a mask technique that can produce trains of bunches with variable spacing in the sub-picosecond range*. This 60 MeV train with one to five drive bunches and a trailing bunch propagates in a 1 to 2 cm long plasma capillary discharge with a variable plasma density. When the plasma density is tuned such that the plasma wavelength is equal to the drive bunches spacing the plasma wakefield is resonantly excited. The distance between the last drive bunch and the trailing bunch is one and a half time that between the drive bunches, putting the trailing bunch in the accelerating phase of the wakefield. The resonance is characterized by a maximum energy loss by all the drive bunches and maximum energy gain by the trailing bunch. Experimental results will be presented.
*P. Muggli et al., Phys. Rev. Lett. {10}1, 054801, 2008
UCLA, Los Angeles, California
BNL, Upton, Long Island, New York
Funding: Work supported by US Department of Energy.
At the BNL-ATF we have recently demonstrated the generation of trains of electron with sub-picosecond spacing*. These trains of equidistant bunches can be used to resonantly excite large amplitude wakefields in plasmas. The resonance is reached when the plasma wavelength is equal to the drive bunch train spacing. However, in order accelerate an electron bunch with a narrow energy spread, a trailing witness bunch must be generated. The witness bunch must be separated from the last drive bunch by one and a half time the distance between drive bunches. We show that such a drive/witness bunch train can be generated. The mask can also be designed to produce witness bunches trailing the drive bunch train by 2.5,3. 5, times the drive bunch spacing in order to probe the coherence of the plasma wake in subsequent wave bucket. Resonantly driving plasma wakes with trains of bunches could lead to multiplication of the trailing bunch energy by up to the number of bunches in the drive train with high efficiency in a single stage. Experimental results will be presented.
* P. Muggli et al., Phys. Rev. Lett. {10}1, 054801, 2008
USC, Los Angeles, California
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
Funding: Work supported by US Department of Energy.
Plasma Wakefield Accelerator has been proven to be a promising technique to lower the cost of the future high energy colliders by offering orders of magnitude higher gradients than the conventional accelerators. However, it has been shown that ion motion is an important issue to account for in the extreme regime of ultra high intensities and ultra low emittances, characteristics of future high energy colliders. In this regime, the transverse electric field of the beam is so high that the plasma ions cannot be considered immobile at the time scale of electron plasma oscillations, thereby leading to a nonlinear focusing force. Therefore, the transverse emittance of a beam matched to the initial linear focusing will not be preserved under these circumstances. However, Vlasov equation predicts a matching profile even in the nonlinear regime. Furthermore, we extend the idea and introduce a plasma section that can match the entire beam to the mobile-ion regime of plasma. We also find the analytic solution for the optimal matching section. Simulation results will be presented.
USC, Los Angeles, California
UCLA, Los Angeles, California
Funding: Work supported by the US Department of Energy
Studies on propagation of electron beams in plasma have shown that in the blowout regime of the plasma wakefield accelerator (PWFA), the emittance of the incoming beam is preserved because of the linear focusing force exerted by a uniform ion column [1]. However, for positron beams the focusing force is nonlinear and they suffer emittance growth. We simulated the propagation of a positron beam in the uniform plasmas with different densities. We calculated the beam emittance from the simulation results and observed the beam size and emittance grow with increasing plasma density. Simulation results agree well with that of previous work.
UTNL, Ibaraki
RLNR, Tokyo
The University of Tokyo, Nuclear Professional School, Ibaraki-ken
SUT, Noda-shi, Chiba
An all-optical inverse Compton gamma-ray source is enable us to make a tabletop monochromatic gamma-ray source that might be applied to measure an amount of nuclear material, etc. An intense laser pulse excites a very nonlinear plasma wave and accelerate electron bunch up to several-hundreds MeV within a length of a few millimeters. The key to success is stabilization of the laser-plasma accelerators. We are developing the artificial injection technique of initial electrons in to the plasma wave and guiding of the intense laser pulse by the preformed plasma channel.
PPPL, Princeton, New Jersey
Funding: Research supported by the U.S. Department of Energy.
The Paul Trap Simulator Experiment (PTSX) is a compact laboratory Paul trap that simulates a long, thin charged-particle bunch coasting through a kilometers-long magnetic alternating-gradient (AG) transport system by putting the physicist in the frame-of-reference of the beam. Results are presented from experiments in which the axial distribution function is modified by lowering the axial confinement barrier to allow particles in the tail of the axial distribution function to escape. Measurements of the axial energy distribution and the transverse density profile are taken to determine the effects of the modified distribution function on the charge bunch. It is observed that the reduced axial-trapping potential leads to an increase of the transverse effective temperature.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
University of Dundee, Nethergate, Dundee, Scotland
UMAN, Manchester
Accurate determination of the wakefield effects for high intensity, short electron bunches is an area of active research in accelerator design. Of particular interest is the resistive wall wakefield which depends upon the complex conductivity of the vacuum vessel. This conductivity depends on factors such as the frequency of the applied field, the temperature of the vessel and the level of impurities in the vessel material and so is generally difficult to characterise for real vessels. We present an experiment for determining the complex conductivity properties of a cylindrical vessel at frequencies in the THz regime, through the sub-picosecond time-resolved measurement of pulsed THz radiation transmitted through the structure. These results are compared to theoretical calculations.
USC, Los Angeles, California
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
BNL, Upton, Long Island, New York
Funding: Work supported by US Department of Energy.
Current Filamentation Instability, CFI, (or Weibel instability) is of central importance for relativistic beams in plasmas for the laboratory, ex. fast-igniter concept for inertial confinement fusion, and astrophysics, ex. cosmic jets. Simulations, with the particle-in-cell code QuickPic, with a beam produced by an RF accelerator show the appearance and effects of CFI. The instability is investigated as a function of electron beam parameters (including charge, transverse size and length) and plasma parameters (density and length) by evaluating the filament currents and magnetic fields. We present simulation results, discuss further simulation refinements, suggest criteria and threshold parameters for observing the presence of CFI and outline a potential future experiment.