ENEA C.R. Frascati, Frascati (Roma)
INFN/LNF, Frascati (Roma)
Rome University La Sapienza, Roma
LBNL, Berkeley, California
The SPARX X-FEL accelerator will be the first FEL facility to operate with a hybrid (RF plus magnetic chicane) compression scheme. Numerical studies of propagation of beam density modulations stemming from photogun laser, through the photoinjector operating under velocity bunching conditions have been carried out. A semi-analytical model for the linear gain in a RF compressor is also being developed and some preliminary results are presented.
KEK, Ibaraki
JAEA/ERL, Ibaraki
The compact ERL, cERL, is a project to test an energy recovery linac (ERL) with 60 MeV and 100 mA electron beam to generate synchrotron radiation with smaller emittance and shorter pulse length. The design work of the cERL injector has been carried out using a space charge simulation code. The injector consists of 500 kV photo cathode DC gun, two solenoid magnets, buncher cavity, three super conducting RF cavities and merger section to return pass. It generates an electron beam with -77 pC bunch charge and 1.3 GHz repetition rate. Our target value of emittance is less than 1 mm mrad with the bunch length of 1 mm at the exit of the injector. The parameter optimization of the injector using the multi objected method has been carried out to obtain the minimum emittance. The simulation results will be presented in detail.
Technion, Haifa
Funding: This work was supported by the Israel Science Foundation and the Kidron Foundation
We present results of an analysis demonstrating that electrons oscillating in a Penning trap may drain the energy stored in an adjacent active medium. For this process to happen, the electrons must become bunched and the energy imparted to the electrons allows them to leave the trap resulting into a train of bunches. Their angular frequency corresponds to medium’s resonance.
UCLA, Los Angeles, California
Funding: Office of Naval Research (US) Grant No. N000140711174
Longitudinal beam dynamics of the photoinjector "blowout" regime are investigated. A two beamlet macroparticle approach is first used to investigate the effects of S-Band RF photogun fields on a picosecond time scale. The beams' longitudinal phase spaces (LPS) are measured via an X-band RF deflecting cavity and dipole spectrometer. Lastly, the LPS of a single subpicosecond beam is investigated as a function of initial charge density at the cathode and compared to simulation.
Xavier University of Louisiana, New Orleans, Louisiana
UW-Madison/SRC, Madison, Wisconsin
For many years it has been speculated that uniformly filled ellipsoidal electron bunches, with their linear fields, would be ideal to produce high charge density with low emittance beams. This may be particularly advantageous with bunch compression schemes required for operation of an FEL. The “blow-out” mode is a method of producing the desired electron bunch distribution: an initial charge pancake is produced at the cathode and allowed to expand to an ellipsoidal shape under the influence of its own space charge. In earlier studies a constant, DC electric field has been assumed in the production of ellipsoidal bunch distributions using “blow-out” mode. In this paper we look at the effects of a time varying, non-constant electric field on the development of the electron bunches as they are emitted from the photocathode and travel through an accelerating RF cavity. We present the effects of frequency in the cavity, field strength of the cavity,, as well as the phase of the electron bunch. These three variables change the spatial curvature and the temporal slope of the electric field as observed by the electron bunch. This results in changes in bunch development and formation.
Tech-X, Boulder, Colorado
KEK, Ibaraki
BNL, Upton, Long Island, New York
Funding: Supported in part by the DOE Office of Science, Office of Nuclear Physics under grant No. DE-FG02-06ER84508.
Non-scaling FFAGs are sensitive to a slew of resonances during the acceleration ramp. An important consideration - because it affects the amount of rf power required - will be the speed at which resonances must be crossed. We present simulations of possible non-scaling FFAGs, focusing especially on the effects of space charge, using newly developed capabilities in the code PTC*.
* E. Forest, Y. Nogiwa, F. Schmidt, "The FPP and PTC Libraries", ICAP'2006.
Fermilab, Batavia
Funding: Work supported by US DOE under Contract No. DE-AC02-07CH11359
CHEF is body of software dedicated to accelerator beam dynamics and optics computations. It consists in a hierarchical set of libraries and a standalone application based on the latter. The code makes extensive use of templates and modern idioms such as smart pointers and generalized function objects. CHEF has been described in contributions at past conferences. In this paper, we document and discuss the implementation of recent improvements including:
- use of embedded SQL database technology to store, organize and retrieve lattice function data,
- a general approach to "knobs" based on generalized function objects,
- an improved architecture to support runtime plug-in propagation physics,
- a basic space-charge kick element,
- a facility to record particle loss on aperture boundaries and
- support for the MADX input format.
CLASSE, Ithaca, New York
Cornell University, Ithaca, New York
JLAB, Newport News, Virginia
Cornell University has built a high average current electron injector for use with an Energy Recovery Linac. The injector is capable of up to 100 mA average current at 5 MeV (33 mA at 15 MeV) and is expected to produce the ultra low emittances needed for an ERL. This talk will give an overview of the initial performance of this injector and summarize a spectrum of beam physics experiments undertaken to demonstrate low emittance, high average current operation.
ISIR, Osaka
KEK, Ibaraki
Ultrafast time-resolved electron diffraction based on a photocathode rf electron gun is being developed in Osaka University to reveal the hidden dynamics of intricate molecular and atomic processes in materials. The photocathode rf gun generates a femtosecond-bunch electron beam by femtosecond laser driving. The transverse emittance, bunch length and energy spread were measured. The growths of the emittance, bunch length and energy spread due to the rf and the space charge effects in the rf gun were investigated by changing the laser injection phase, the laser pulse width and the bunch charge. The demonstration of the electron diffraction measurement will be reported.
J-PARC, KEK & JAEA, Ibaraki-ken
For operation of the JPARC Main Ring, low loss of the high-intensity bunches during the injection and acceleration processes is crucial to avoid radiation damage of the machine. This requires identification and correction the most dangerous resonances, which should be done in combination with the collective effects, in particular, the low energy space charge effects. In frame of this talk we review the status of the Main Ring commissioning process and compare it with the simulation results for the low intensity beam. For the future operation of the Main Ring with the moderate beam power we review the status of the simulation work and discuss the budget of the beam losses.
GSI, Darmstadt
ORNL, Oak Ridge, Tennessee
IAP, Frankfurt am Main
CEA, Gif-sur-Yvette
Funding: We acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 ‘‘Structuring the European Research Area’’ program (CARE, Contract No. RII3-CT-2003-506395).
Beam dynamics experiments with high intensity beams have been conducted at the GSI UNILAC in 2006-2008 with the goal of benchmarking four major simulation codes, i.e. DYNAMION, PARMILA, TraceWin/PARTRAN and LORASR with respect to transverse emittance growth along a DTL. The experiments comprised measurements of transverse phase space distributions in front of as well as behind the DTL. Additional longitudinal bunch length measurements at the DTL entrance allowed for estimate and control of mismatch in all three planes. Measured effects of mismatch and of theoretically predicted space charge resonances (equipartitioning and others) are compared with simulations for a wide range of transverse phase advance along the DTL. This contribution is the first report on the successful measurement of a space charge driven fourth order resonance in a linear accelerator.
GSI, Darmstadt
The effect of space charge on the transverse Schottky spectrum of coasting and bunched beams is studied using measurements and simulations together with analytic models. The measurements of transverse Schottky bands from heavy ion beams are performed in the SIS-18 synchrotron at GSI. In addition we analyze the noise spectrum from a particle tracking code with self-consistent space charge. Both results are compared to analytic models for coasting and for bunched beams with space charge. For coasting beams an analytic model based on the transverse dispersion relation with linear space and chromaticity reproduces the characteristic deformation of Schottky bands with increasing space charge, observed in both measurement and simulation. For bunched beams we find good agreement between the observed shifts of synchrotron satellites and a simplified model for head-tail modes with space charge. The relevance of the results for the analysis of transverse beam stability in the presence of space charge is emphasized.
TUB, Beijing
PSI, Villigen
CIAE, Beijing
In high intensity cyclotrons with small turn separation, both the space charge effects of single bunch and the interaction of radially neighbouring bunches play important roles. A PIC-based three-dimensional parallel code, OPAL-CYCL, is newly developed under OPAL framework which self-consistently covers these two collective effects. In this paper we also present the simulation results from the compact cyclotron CYCIAE-100 in the context of the ongoing upgrade program of BRIF at CIAE, with the goal of 100 MeV, 200 μA CW proton beam on target.
NSCL, East Lansing, Michigan
BNL, Upton, Long Island, New York
Funding: this work is supported by National Science Foundation Grant PHY-0606007.
The Small Isochronous Ring (SIR) at the NSCL/MSU was built to study space charge effects in the isochronous regime. Results of experimental studies of the longitudinal beam dynamics in the ring showed a remarkable agreement with results of numerical simulations. Recently, we have designed and built an energy analyzer to accurately measure the beam energy spread. We will present results of energy spread measurements as well as simulations of the beam behavior based on the Vlasov formalism.
Fermilab, Batavia
Rutgers University, The State University of New Jersey, Piscataway, New Jersey
Funding: This manuscript has been authored by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The promise of next-generation light sources depends on the availability of ultra-low emittance electron sources. One method of producing low transverse emittance beams is to generate a low longitudinal emittance beam and exchange it with a large transverse emittance. Experiments are underway at Fermilab's A0 Photoinjector and ANL's Argonne Wakefield Accelerator using the exchange scheme of Kim and Sessler. Experiments as the A0 photoinjector exchange a large longitudinal emittance with a small trasverse emittance. AWA expects to exchange a large transvserse emittance with a small logitudinal emittance. In this paper we discuss recent results at A0 and AWA and future plans for these experiments.
BNL, Upton, Long Island, New York
Funding: This work supported by the U.S. Department of Energy, contract no. DE-AC02-98CH10886.
Beam cooling for a future neutrino factory or muon collider requires high gradient rf cavities in the presence of strong magnetic fields. Experimental measurements suggested that the maximum accelerating gradient drops as the axial magnetic field increases. Little is known about the explicit dependence of the gradient on the strength of the magnetic field. The experimental observation of dark currents arising from local regions with enhanced surface field intensities under external magnetic fields however, suggests a new possible mechanism of breakdown based on electron field emission. A model of magnetic field breakdown is proposed. We illustrate that the field emitted electrons are focused by the external fields into small spots on the other side of the cavity and estimate the energy density they deliver to the wall. We show that this energy increases with the magnetic field, and this may lead to melting of the cavity surface. The influence of local fields at the emitter side is discussed and the extent to which space-charge affects this process is investigated. Results of our model are compared with recent experimental data from the 201 MHz and 805 MHz cavities.
Fermilab, Batavia
Injection painting enables the mitigation of space charge and stability issues, and may be indispensable for the Project-X at Fermilab, delivering high-intensity proton beams to HEP experiments. Numerical simulations of multi-turn phase space painting have been performed for the FNAL Recycler Ring, including a self-consistent space charge model, lattice nonlinearities, H- stripping, particle loss and foil heating. Different painting waveforms were studied to build a uniform (KV-like distribution) and other phase space distributions.
CERN, Geneva
The CERN Proton Synchrotron Booster (PSB) has been running for more than 30 years. Originally designed to accelerate particles from 50 to 800 MeV, later upgraded to an energy of 1 GeV and finally 1.4 GeV, it is steadily being pushed to its operational limits. One challenge is the permanent demand for intensity increase, in particular for CNGS and ISOLDE, but also in view of LINAC4. As it is an accelerator working with very high space charge during the low energy part of its cycle, its operational conditions have to be precisely tuned. Amongst other things resonances must be avoided, stop band crossings optimized and the machine impedance minimized. Recently, an operational intensity record was achieved with >4.25·1013 protons accelerated. An orbit correction campaign performed during the 2007/2008 shutdown was a major contributing factor to achieving this intensity. As the PSB presently has very few orbit correctors available, the orbit correction has to be achieved by displacing and/or tilting some of the defocusing quadrupoles common to all 4 PSB rings. The contributing factors used to optimize performance will be reviewed.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
LASTI, Hyogo
Hiroshima University, Graduate School of Science, Higashi-Hiroshima
KEK, Ibaraki
J-PARC, KEK & JAEA, Ibaraki-ken
The beam commissioning of the J-PARC 3-GeV RCS started in October 2007. The initial machine parameter tuning and underlying beam studies were completed in February 2008 through various beam dynamics measurements, such as optical functions, turn-by-turn beam positions, and transverse and logitudinal beam profiles. Now the RCS is in transition from the first commissioning phase to the next challenging stage and our efforts hereafter will be focused on higher beam power operations. In this paper, we describe experimental results obtained in the high intensity demonstrations in October 2008, together with the corresponding simulation results.
Fermilab, Batavia
Head-tail modes are described when the space charge tune shift significantly exceeds the synchrotron tune. Spatial shape of the modes, their frequencies, coherent growth rates and Landau damping rates are found.
BNL, Upton, Long Island, New York
UMD, College Park, Maryland
JLAB, Newport News, Virginia
Funding: This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office
In this paper we report on a proof of principle experiment for demonstrating the possibility of reconstructing the time resolved-phase-space distribution of a space-charge dominated beam by a tomographic technique which provides us with far more information than a time-sliced emittance. We emphasize that this work describes and demonstrates a new methodology which can be applicable to any beam pulse using imaging methods with the appropriate time resolution for the pulse duration. The combination of a high precision tomographic diagnostic with fast imaging screens and a gated camera are used to produce phase space maps of two beams: one with a parabolic current profile and another with a short perturbation atop a rectangular pulse. The correlations between longitudinal and transverse phase spaces are apparent and their impact on the dynamics is discussed.
ORNL, Oak Ridge, Tennessee
Funding: SNS is managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725
The SNS Ring has now been operating for about 2.5 years, and our march continues to increase the beam power to the design value of 1.4 MW. The Ring is a loss-limited machine, and in general the radioactivation levels are good, but there are some unanticipated hot spots that we are working to relieve. Beam optics functions have been measured using the model independent and orbit response matrix methods, and our results will be compared to the ideal model. High-intensity beam profiles measurements show space-charge effects, and these will be compared to model calculations. We will also discuss the status of equipment upgrades that are now in progress in the high-energy beam transport momentum dump, the injection-dump beam line, and in the ring-to-target beam line.
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.
CEA, Gif-sur-Yvette
INFN/LNL, Legnaro (PD)
During the EVEDA (Engineering Validation and Engineering Design Activities) phase of the IFMIF (International Fusion Materials Irradiation Facility) project, a 125 mA/9 MeV accelerator prototype will be built, tested and operated in Rokkasho-Mura (Japan). The injector section of this accelerator is composed by an ECR source, delivering a 140 mA deuteron beam at 100 keV, and a low energy beam transport (LEBT) line required to match the beam for the RFQ injection. The proposed design for the LEBT is based on a dual solenoids focusing scheme. In order to takes into account the space charge compensation of the beam induced by the ionisation of the residual gas, a 3D particle-in-cell code (SOLMAXP) has been developed for the beam dynamics calculations. The LEBT parameters have been optimized in order to maximize the beam transmission through the RFQ. The final LEBT design, as well as the simulation results, are presented.
CEA, Gif-sur-Yvette
INFN/LNL, Legnaro (PD)
CIEMAT, Madrid
The two IFMIF (International Fusion Materials Irradiation Facility) accelerators will each have to deliver 5 MW of deuteron beam at 40 MeV. To validate the conceptual design, a prototype, consisting of one 9 MeV accelerator called EVEDA (Engineering Validation and Engineering Design Activity), is being constructed. Beam dynamics studies are entering the final phase for the whole EVEDA and for the accelerating part of IFMIF. The challenging point is to be able to reconcile the very strong beam power and the hands-on maintenance constraint. At energies up to 5 MeV, difficulties are to reach the requested intensity under a very strong space charge / compensation regime. Over 5 MeV, difficulties are to make sure that beam losses can be maintained below 10-6 of the beam intensity. This paper will report the strategies and choices adopted in the optics design and the beam measurement proposal.
CERN, Geneva
To understand one contribution to the intensity limitations of the CERN Proton Synchrotron Booster (PSB) in view of its operation with beams from Linac 4, the impedance of the machine has been characterized. Measurements of tune shift as a function of the intensity have been carried out in order to estimate the low frequency imaginary part of the impedance. Since the PSB is a low energy machine, these measurements have been done at two different energies,so as to enable us to disentangle the effect of the indirect space charge and resistive wall from the contribution of the machine impedance. An estimation of the possible resonant peaks in the impedance spectrum has been made by measuring a fast instability in Ring 4.
CERN, Geneva
The HEADTAIL code models the evolution of a single bunch interacting with a localized impedance source or an electron cloud, optionally including space charge. The newest version of HEADTAIL relies on a more detailed optical model of the machine taken from MAD-X and is more flexible in handling and distributing the interaction and observation points along the simulated machine. In addition, the option of the interaction with the wake field of specific accelerator components has been added, such that the user can choose to load dipolar and quadrupolar components of the wake from the impedance database Z-BASE. The case of a single LHC-type bunch interacting with the realistic distribution of the kicker wake fields inside the SPS has been successfully compared with a single integrated beta-weighted kick per turn. The current version of the code also contains a new module for the longitudinal dynamics to calculate the evolution of a bunch inside an accelerating bucket.
Fermilab, Batavia
The proposed Mu2e experiment will present a number of challenges for the Fermilab accelerator complex. The Accumulator and Debuncher rings of what is currently the antiproton complex will be required to handle proton beams with intensities several orders of magnitude larger than the antiproton beams they now carry, leading to a substantial space-charge tune shift. The protons will be then be extracted from the Debuncher using resonant extraction. We present results from simulations of 3D space charge effects for Mu2e beam parameters, with emphasis on how they affect the resonant extraction process.
Fermilab, Batavia
The Synergia framework has been enhanced to include new Poisson solvers and new collective physics effects. Synergia now includes Sphyraena, a solver suite that provides the ability to handle elliptical beam pipes. Resistive wall effects, including intra- and inter-bunch effects in the presence of multiple bunches are also available. We present an overview of the updates in Synergia, focusing on these developments.
GSI, Darmstadt
The conservation of the longitudinal beam quality through the SIS-18/100 synchrotron chain is of major importance for the FAIR accelerator project as well as for the SIS-18 upgrade. The generation of a short, intense heavy ion bunch at the end of the machine cycle defines a tight budget for the tolerable longitudinal emittance growth. Potential sources of bunch quality degradation are intensity effects and non-adiabatic rf ramps during the rf capture in SIS-18 and during the barrier bucket pre-compression in SIS-100. The time spend on rf manipulations has to be as small as possible in order to maximize the repetition rate. We report about theoretical and experimental studies in SIS-18 of optimized voltage ramps for rf capture into single and double rf buckets, including space charge and beam-loading effects. Further we show that longitudinal space charge can improve the efficiency of rf manipulations. As an example we present an optimized barrier bucket pre-compression scheme for SIS-100.
GSI, Darmstadt
The prediction of beam loss for long term storage of a high intensity beam is a challenging task essential for the SIS100 design. On this ground an experimental campaign using a high intensity beam has been performed at GSI on the SIS18 synchrotron with the purpose of extending a previous benchmarking experiment made at the CERN-PS in the years 2002-2003. We report here the results of this experimental campaign and the benchmarking with the simulation predictions.
GSI, Darmstadt
MEPhI, Moscow
Beam loss control in SIS100 is relevant for the design of collimators and for maintaining vacuum quality. We present the status of the studies of beam degradation, due to space charge and magnet imperfections during the accumulation at injection energy. The impact of magnet misalignment on resonances and beam trapping/scattering effects is discussed.
GSI, Darmstadt
IHEP Beijing, Beijing
In the conventional design of rf linacs, the space-charges are not in three-dimension thermal equilibrium. The space-charge couples the longitudinal and transverse will cause equipartitioning process which causes the emittance growth and the halo formation. In the design of the Chinese Spallation Neutron Source (CSNS) linac], three cases are investigated using the Hofmann stability charts to analysis and optimize the layout. In this paper, we present the equipartitioning beam study of the CSNS Alvarez DTL linac.
KEK, Ibaraki
Crossing different types of resonances is unavoidable for the high beam power operation of the JPARC Main Ring. The ‘lattice’ resonances are cause by the realistic machine imperfection including the field and alignment errors. In addition the ‘space charge’ resonances will lead to the emittance growth. The mechanism of the emittance dilution for the realistic machine imperfection in combination with the space charge effects should be studied in the self-consistent manner. In frame of this report we analyze different coherent modes of the space charge dominated beam at the injection energy for the JPARC Main Ring for some basic operation scenario of the machine. This analysis allows to identify the most dangerous resonances and to understand the effect of the emittance dilution remaining after the resonance correction. The study has been performed by using the PTC{}ORBIT code.
LLNL, Livermore, California
UMD, College Park, Maryland
Funding: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Mismatch oscillations resulting from the propagation of space charge waves in intense beams may lead to halo generation and possible beam loss, and modify longitudinal beam dynamics. These oscillations have amplitudes and frequencies different from that of the main beam and are particularly important in machines such as the University of Maryland Electron Ring (UMER), in which the beam dynamics scale to parameters associated with heavy ion fusion drivers. We use the particle-in-cell (PIC) code, LSP, to simulate space charge wave dynamics in an intense electron beam propagating in a smooth focusing channel with 2-D cylindrical symmetry. We examine the evolution of linear and nonlinear density perturbations in the UMER parameter range for both matched and mismatched beams. Comparisons between LSP simulations and numerical models are presented.
ANL, Argonne
We developed a moving window algorithm for the SEDG time-domain code, NekCEM, for wake field calculations. NekCEM is a highly efficient and spectrally accurate electromagnetic solver using the spectral element discontinuous Galerkin (SEDG) method based on body-fitted spectral element hexahedral meshes. When the domain of interest is around a moving bunch within a certain distance, one does not need to carry out full domain simulations. Moving window approach has been a natural consideration in such circumstance to have significant reduction in computational cost for the conventional low-order methods such as FDTD method. However, there have not been studies on the high-order methods, especially the SEDG method, based on the moving window approach. We implemented 3D moving window option for wake field calculations on various conducting cavities including the 9-cell TESLA cavity. We will demonstrate the performance of the SEDG simulations on moving window meshes.
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.
CLASSE, Ithaca, New York
LBNL, Berkeley, California
Funding: Support provided by the US National Science Foundation and the US Department of Energy
The Cornell Electron Storage Ring (CESR) has recently begun operation as a test accelerator for next generation linear collider damping rings. This program, known as CesrTA, includes a thorough investigation of synchrotron radiation generated electron cloud effects. CESR is capable of operating with a variety of bunch patterns and beam currents, as well as with both electron and positron beams. Understanding the buildup of the cloud under these conditions requires the use of well validated simulation programs. This paper will discuss three such programs- POSINST, ECLOUD and CLOUDLAND, which have been benchmarked against each other in parameter regimes relevant to CesrTA operating conditions, with the aim of understanding systematic differences in the calculations.
ENEA C.R. Frascati, Frascati (Roma)
In this paper the Fast Multipole Approximation is described with regard to the problem of modelling self fields effects in low emittance, high brightness electron beams of interest for future accelerators and light sources. This well established technique is known to scale as O(N) or O(N log N) (depending on details of the implementation) with the number of particles involved in the simulation. Performances and results as a standalone technique or as a method for for fast calculation of boundary conditions together with other approaches based on PDEs are discussed, along with details of a parallel implementation in the tracking code Tredi.
IIT, Chicago, Illinois
Illinois Institute of Technology, Chicago, Illinois
Fermilab, Batavia
Muons, Inc, Batavia
Funding: Supported in part by USDOE Contract DE-FG02-6ER86281
The study of Muon beam optics is crucial for future Neutrino Factory and Muon Collider facilities. At present, the GEANT4-based simulation tools for Muon beam tracking such as G4beamline and G4MICE are based on single particle tracking without collective effects taken into account. However, it is known that collective effects such as space charge and wakefields for muons (in matters or vacuum) are not ignorable. As the first step, space charge computation has been implemented into muon tracking. The basic algorithm is particle to particle interactions through retarded electro-magnetic fields. The momentum impulse by collective effects is imposed on every particle at each collective step, and the G4beamline main code is used for tracking. Comparisons to LANL Parmela are illustrated and analyzed. Optimizations of the algorithm are also underway to gain less computing time and more accuracy. Moreover, the idea of enhancing ionization cooling efficiency by utilizing the collective effect due to polarized charges in matter appears to be possible, and the preliminary estimation has been done.
IUCF, Bloomington, Indiana
Funding: This work is supported by AFOSR under grant FA9550-08-1-0160.
We present the theoretical and numerical results of a dispersion free time-dependent Green's function method which can be utilized for calculating electromagnetic space-charge fields due to arbitrary current in a conducting pipe. since the Green's function can be expanded in terms of solutions to the wave equation, the numerical solutions to the fields also satisfy the wave equation yielding a completely dispersion free numerical method. This technique is adequately suited for modeling bunched space-charge dominated beams, such as those found in high-power microwave sources, for which the effects of numerical grid dispersion and numerical Cherenkov radiation are typically found when using FDTD type methods.
IUCF, Bloomington, Indiana
ANL, Argonne
Funding: Supported in part by DOE(DE-FG029ER40747) and in part by NSF(PHY-0552389)
Near the cathode in a photoinjector, the electron beam is emitted with low energy, and its dynamics are strongly affected by the beam's space-charge fields. This can cause beam loss at the cathode due to virtual cathode formation. In general, a fully electromagnetic code can correctly predict the beam space-charge fields, beam dynamics, and beam loss. However, an electrostatic type algorithm would overestimate the space-charge fields since it does not incorporate relativistic time-retardation effects which limit the size of the fields near the cathode. IRPSS (Indiana RF Photocathode Source Simulator) can calculate the electromagnetic space-charge fields using a Green’s function method to a high-precision, and can track beam dynamics in the RF photoinjector. Using IRPSS, we simulated the beam dynamics and beam loss near the cathode for the Argonne Wakefield Accelerator 1.3 GHz gun* and compared those results to electrostatic codes, such as PARMELA and ASTRA.
*P. Schoessow, PAC 2009.
Muons, Inc, Batavia
Funding: Supported in part by USDOE Contract DE-FG02-6ER86281.
The G4beamline program is based on the well-established Geant4 toolkit used to simulate the interactions of particles and photons with matter. Until now, only a single particle at a time could be tracked and there are no interactions between particles. Recent designs for high pressure RF cavities and other novel devices achieving extreme muon cooling require that the effect of space charge be included in the simulations. A new tracking manager in G4beamline propagates a number of particles (typically 1,000-10,000) in parallel, stepping all particles in time. This allows all of the usual Geant4 physics interactions to be applied, plus collective computations. A simple macroparticle-based model is used to represent ~108 charges with an ellipsoidal charge density. At intervals the appropriate macroparticle size and shape are recalculated, the electric and magnetic fields are determined, and an impulse is applied to the simulated particles. Comparisons to standard space charge codes are presented.
Muons, Inc, Batavia
Illinois Institute of Technology, Chicago, Illinois
IIT, Chicago, Illinois
Funding: Supported in part by USDOE STTR Grant DE-FG02-06ER86281
Most computer programs that calculate the trajectories of particles in accelerators assume that the particles travel in an evacuated chamber. The development of muon beams, which are needed for muon colliders and neutrino factories and are usually required to pass through matter, is limited by the lack of user-friendly numerical simulation codes that accurately calculate scattering and energy loss in matter. Geant4 is an internationally supported tracking toolkit that was developed to simulate particle interactions in large detectors for high energy physics experiments, and includes most of what is known about the interactions of particles and matter. Geant4 has been partially adapted in a program called G4beamline to develop muon beam line designs. The program is now being developed and debugged by a larger number of accelerator physicists studying muon cooling channel designs and other applications. Space-charge effects and muon polarization are new features that are being implemented.
BNL, Upton, Long Island, New York
Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Continuing interest in computing the coupling impedance of cylindrical multi-layer beam tubes led to several recent publications. A novel matrix method is here presented in which radial wave propagation is treated in analogy to longitudinal transmission lines. Starting from the Maxwell equations the solutions for monopole and dipole electromagnetic fields are in each layer described respectively by a 2×2 and 4×4 matrix. Assuming isotropic material properties within one layer, the radially transverse field components at the inner boundary of a layer are uniquely determined by matrix transfer of the field components at its outer boundary. By imposing power flow constraints on the matrix, field matching between layers is enforced and replaced by matrix multiplication. The wall impedance is found as eigen solution to the scalar Helmholtz equation with the additional boundary condition that the longitudinal magnetic field vanishes at the inner beam tube wall. The matrix method is demonstrated via the example of the longitudinal impedance of a multi-layer HOM absorber, involving a ceramic tube with metal coating and an external ferrite layer.
IHEP Beijing, Beijing
A set of IPM system will be built on RCS of CSNS to measure vertical and horizontal beam profiles. Detailed conceptual design of an IPM system for CSNS is described in this paper. Wire electrodes are introduced to get a more uniform electric field, and a ‘C’ type electromagnet is designed to exert a uniform magnetic field to the ionization area. The magnetic field is parallel with the sweeping electric field and will inhibit the defocusing effects of space charge and recoil momentum.
CERN, Geneva
At present, for most LHC type physics beams, six buckets of the PS operated with harmonic number h=7 are filled in two transfers, and each of the PS Booster rings provides only one bunch. The scheme presented aims at replacing the double batch transfer by a single batch transfer and is of interest (i) for the nominal 25 ns LHC beams once the Booster injection energy has been increased after completion of Linac4 and (ii) already now for 50 ns and 75 ns LHC beams less demanding for the Booster in terms of beam brightness. Two bunches with the correct spacing must be generated in the Booster rings by superposition of an h=2 RF system and a smaller h=1 component. Theoretical considerations and first experimental results will be presented.
Northern Illinois University, DeKalb, Illinois
UMD, College Park, Maryland
We undertake a study of the single particle dynamics in a model of the University of Maryland Electron Ring. This accelerator uses a low energy electron beam to study the effects of space charge on beam dynamics. However, due to this low energy, other effects that are seldom taken into account in high energy accelerators become important to the single particle dynamics of the beam. The simulation is performed using COSY Infinity, which has the effects of the earth’s magnetic field added to it. When the simulated trajectories are compared to measured beam positions there is good agreement through the ninth section of the ring, at which point the difference between predicted and observed diverges. A method of calculating map elements corresponding to the measured data will be used to determine where issues with the ring that could cause these problems might be found.
Northern Illinois University, DeKalb, Illinois
ANL, Argonne
Funding: M.R. and P.P. was supported by the US DOE under Contracts No. DE-FG02-08ER41532 with NIU. W.G. and J.P are supported by the U.S. DOE under Contract No. DE-AC02-06CH11357 with ANL.
Transverse to longitudinal phase space manipulation hold great promises, e.g., as a potential technique for repartitioning the emittances of a beam. A proof-of-principle experiment to demonstrate the exchange of a low longitudinal emittance with a larger transverse emittance is in preparation at the Argonne Wakefield Accelerator using a 15 MeV electron beam. In this paper we explore the limiting effects of this phase space manipulation method associated to high order optics and collective effects. A realistic start-to-end simulation of the planned proof-of-principle experiment including jitter studies is also presented.
BINP SB RAS, Novosibirsk
The beam is injected into the CLIC damping ring with the relatively large emittance and energy spread and then is damped to the extremely low phase volume. During the damping process the betatron frequency of each particle changes due to the space charge tune shift and nonlinear detuning produced by the chromatic sextupoles, wiggler nonlinear field components and by the space charge force. During the damping, the particle cross resonances, which can trap some fraction of the beam, cause the loss of intensity, the beam blow up and degrade the beam quality. In this paper we study the evolution of the beam distribution in time during the damping.
CLASSE, Ithaca, New York
Commissioning of a new high brightness electron source for the Energy Recovery Linac at Cornell University is currently underway. Despite the fact that the beam dynamics in this portion of the accelerator is space-charge dominated, a fundamental understanding of the machine linear optics is crucial in that it determines the effectiveness of space-charge emittance compensation methods, as well as provides the means to achieving various beam parameters such as beam length and energy spread. Here we introduce a new numerical tool being used in the commissioning of the injector that provides linear optics matrix calculation using field maps for various optical elements.
LBNL, Berkeley, California
LLNL, Livermore, California
Funding: Supported in part by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
In 1958, Courant and Snyder analyzed the problem of alternating-gradient beam transport and treated a model without focusing gaps or space charge.* We extend their work to include the effect of gaps (still neglecting space charge) and obtain exact solutions for the matched envelopes.** We assume a periodic lattice of quadrupole doublets. The focus sections have piecewise-constant field strength and equal lengths, but the zero-field drift sections have arbitrary length ratio. We obtain and show the exact envelope results as functions of z for various field strengths, occupancies (eta), and gap-length ratios. We show the peak envelope excursion as a function of field strength or phase advance (σ) for various cases. There is a broad σ range over which the minimum peak varies less than ± 1%. For eta = 1, this range is 64 to 98 degrees; for eta = 0.5, it is 62 to 96 degrees. In the lowest stable band, the optimum field strength rises by 37.6% when eta is reduced from 1.0 to 0.5 and rises by 76.0% if also one gap has zero length. In the second stable band, the higher field strength accentuates the remarkable compression effect predicted for the FD (gapless) model.**
*E.D. Courant and H.S. Snyder, Ann. Phys. 3, 1 (1958).
**The present work extends a recent envelope analysis carried out without gaps (O.A. Anderson and L.L. LoDestro, submitted to Phys. Rev. ST-AB).
PPPL, Princeton, New Jersey
Funding: Supported by the U.S. Department of Energy.
For applications of high-intensity beams in heavy ion inertial confinement fusion and high energy density physics, solenoidal focusing lattice and transverse wobblers can be used to achieve uniform illumination of the target and for suppressing deleterious instabilities. A generalized self-consistent Kapchinskij-Vladimirskij solution of the nonlinear Vlasov-Maxwell equations is derived for high-intensity beams in a solenoidal focusing lattice with transverse wobblers. The cross-section of the beam is an ellipse with dynamical centroid, titling angle, and transverse dimensions that are determined from 5 envelope-like equations.
TRIUMF, Vancouver
Injection from an external ion source into a cyclotron results in unavoidable emittance growth when the cyclotron's pole gap is not small compared with the first turn radius. In such a congested geometry, the injected beam first has the two transverse directions coupled on entering the axial magnetic field of the cyclotron, then transverse and longitudinal phase spaces are coupled by the inflector. Generally, to avoid loss, the beam is focused tightly through the inflector. It thus arrives at the first turn strongly mismatched because the vertical focusing in such a cyclotron is rather weak (vertical tune < 0.3). Space charge exacerbates the mismatch because it depresses the vertical tune further. Emittance growth from all these effects can be calculated using the full Sacherer 6D envelope formalism. We develop the technique to include cyclotrons and in particular the transverse optics of the rf gaps, and apply it in particular to the re-design of the TRIUMF 300 keV vertical injection line.
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.
Northern Illinois University, DeKalb, Illinois
ANL, Argonne
Funding: M.R. and P.P. was supported by the US DOE under Contracts No. DE-FG02-08ER41532 with NIU. W.G., J.P., and Z.Y. are supported by the U.S. DOE under Contract No. DE-AC02-06CH11357 with ANL.
We report on a new experimental study of the space charge effect in a space-charge-dominated multi-beam electron bunch. A 5 MeV electron bunch, consisting of a variable number of beamlets separated transversely, was generated in a photoinjector and propagated in a drift space. The collective interaction of these beamlets was studied for different experimental conditions. The experiment allowed the exploration of space charge effects and its comparison with three-dimensional particle-in-cell simulations. Our observations also suggest the possible use of a multi-beam configuration to tailor the transverse distribution of an electron beam.
Pulsar Physics, Eindhoven
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
TUE, Eindhoven
The required strengths of quadrupoles in a phase-space tomography section are significantly affected by the total charge per bunch. Finding settings at a high charge is challenging because of the non-linear nature of Coulomb interactions. This is further hindered by the inability to use thin-lens approximations and dependence on numerical simulations. Finally, one faces the problem that at some charge there simply is no solution at all. In this contribution we describe a simple procedure, implemented in the General Particle Tracer (GPT) code, which can be used to find optimal beamline settings in the presence of space-charge forces. The recipe 'transports' the settings for a zero-charge solution to those of the desired charge and it gives an indication what the maximum tolerable charge is.
STFC/RAL/ISIS, Chilton, Didcot, Oxon
ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on a 50 Hz proton synchrotron, which accelerates ~3·1013 ppp from 70 to 800 MeV, corresponding to beam powers of 0.2 MW. Beam loss imposes limits on operational intensity, and a main contributing mechanism is the action of half integer resonance under high space charge. The same loss mechanism is also a potential problem in ISIS upgrade scenarios involving either higher energy injection into the existing ring, or the addition of a new 3 GeV, high intensity RCS. Progress on particle in cell simulation studies investigating the effects of the driven coherent envelope motion, the associated parametric halo, along with implications of momentum spread, dispersion and longitudinal motion, is reported. Where possible, comparisons are made with relevant theoretical models. Closely related benchmarking work, experimental studies and plans are also summarised.
STFC/RAL/ISIS, Chilton, Didcot, Oxon
ISIS is the pulsed neutron and muon source based at the Rutherford Appleton Laboratory in the UK. Operation is centred on a loss-limited 50 Hz proton synchrotron which accelerates ~3·1013 protons per pulse from 70 MeV to 800 MeV, corresponding to mean beam powers of 0.2 MW. A number of ISIS upgrades are currently under study. One option replaces the linac for higher energy injection into the existing ring, potentially increasing beam current through reduction in space charge. The other main option adds a new 3 GeV RCS, boosting the energy of the beam to provide higher beam power. For both these upgrade routes, longitudinal dynamics of the existing and proposed new rings play a crucial role in achieving high intensity with low loss. This paper outlines longitudinal beam dynamics studies in the rings for both these cases, including development of a new longitudinal space charge code, comparison of different algorithms and codes and treatment of the key beam dynamics issues for each case. The influence of non-space charge impedances is also considered.
JLAB, Newport News, Virginia
Funding: This work is supported under U.S. DOE Contract No. DE-AC05-06OR23177.
When an electron bunch with initial linear energy chirp traversing a bunch compression chicane, the bunch interacts with itself via coherent synchrotron radiation (CSR) and space charge force. The effective longitudinal CSR force for a 2D energy-chirped gaussian bunch on a circular orbit has been analyzed earlier*. In this paper, we present our analytical results of the effective longitudinal CSR force for such a bunch going through a general orbit, which includes the entrance and exit of a circular orbit.
*R. Li, Phys. Rev. ST Accel. Beams 11, 024401 (2008).
JLAB, Newport News, Virginia
UMD, College Park, Maryland
BNL, Upton, Long Island, New York
Funding: This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office
Longitudinal space-charge waves can introduce energy perturbations into charge particle beams and degrade the beam quality, which is critical to many modern applications of particle accelerators. Although many longitudinal phenomena arising from small perturbations can be explained by a one-dimensional cold fluid theory, nonlinear behavior of space-charge waves observed in experiments has not been well understood. In this paper, we summarize our recent investigation by means of more detailed measurements and self-consistent simulations. Combining the numerical capability of a PIC code, WARP, with the detailed initial conditions measured by our newly developed time resolved 6-D phase space mapping technique, we are able to construct a self consistent model for studying the complex physics of longitudinal dynamics of space-charge dominated beams. Results from simulation studies suggest that the unexplained nonlinear behavior of space-charge waves may be due to transverse mismatch or misalignment of beams.
IF-UFRGS, Porto Alegre
The question is whether an anisotropic system of collisionless particles coupled by long-range space-charge forces will equipartition and, if so, how. Results show that collective effects tend to cause an initial beam with strongly nonuniform density to relax, rapidly, to a state that is equlibrium-like. In order to understand the initial dynamical behavior of an anisotropic beams, in particular, to study possible mechanisms of equipartition connected with phase space we have to know how we can compute the variables (volume, area of surface, and area projected) that characterize the anisotropic beam in phase space. The purpose of this paper is to propose one definiton of the anisotropic equipartition. In the state of anisotropic equipartition, the temperature is stationary, the entropy grows in the cascade form, there is a coupling of transversal emittance, the beam develops an elliptical shape with a increase in its size along one direction and there is halo formation along one direction preferential.
UMD, College Park, Maryland
Funding: * This work is funded by US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office.
The containment of beams in the longitudinal direction is fundamental to the operation of accelerators that circulate high intensity beams for long distances such as the University of Maryland Electron Ring (UMER); a scaled accelerator using low-energy electrons to model space-charge dynamics. The longitudinal space-charge forces in the beam, responsible for the expansion of the beam ends, cause a change in energy at the beam head/tail with respect to the main injected energy or flat-top part of the beam. This paper presents the first experimental results on using an induction cell to longitudinally focus the circulating beam within the UMER lattice for multiple turns.
Keywords: electron ring, focusing, induction cell.
UMD, College Park, Maryland
Funding: This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office
The University of Maryland Electron Ring (UMER) can operate over a broader range of beam intensities than other circular machines. Naturally, transverse and longitudinal space charge effects limit the ability to store beams. In UMER, the resonance properties of the machine in the two regimes of operation, emittance- and space charge-dominated transport, differ significantly. We report on studies of linear betatron resonances in UMER from 0.6 mA to 80 mA beam current, corresponding to theoretical space charge incoherent tune shifts well over the Lasslet limit. The observations are related to existing theories as well as to computer simulations. We also describe the instrumentation and techniques used for tune measurements.
UMD, College Park, Maryland
Funding: This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office.
Understanding the dynamics of the acceleration of high-intensity space-charge-dominated electron and ion beam is very important. Accelerating by steps a space-charge-dominated beam can be fundamentally different from beams at lower intensities, because at sufficiently high beam intensities the beam response to acceleration can drive to some unknown instabilities leading to a significant beam losses. This work analyses the acceleration of the University of Maryland Electron Ring (UMER) beam, i.e., high current, low-energy and space-charge-dominated electron beam which is applicable, on a scale basis, to a large class of other beam systems. We use the WARP particle-in-cell code to perform simulations that are compared with theoretical predictions and preliminary experimental results.
UMD, College Park, Maryland
Funding: This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept of Defense Office of Naval Research and Joint Technology Office.
Halo is one important limiting factor for the continuous and reliable operation of intense electron or ion beam facilities, such as FELs and spallation neutron sources. A halo population outside the core of the beam can lead to uncontrolled beam loss, electron cloud effects and activation of the beam pipe, as well as beam quality degradation. In this study, we focus on the issue of halo removal, by means of beam collimation, and subsequent halo regeneration. We compare the particle-core model of halo creation to accurate, self consistent particle-in-cell (PIC) simulations. We show that under certain conditions the halo is regenerated even after collimation. This can only be understood within the context of collective effects, particularly in the case of intense beams.
UMD, College Park, Maryland
Funding: *This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office
The University of Maryland Electron Ring (UMER) is designed for operation over a broad range of beam intensities, including those normally achieved only in linacs. This is possible thanks to a combination of low-energy (10 keV) electrons and a high density of magnetic quadrupoles (72 over an 11.5 m circumference) that allow operation from 0.5 mA to 100 mA; that is, from the emittance dominated to the highly space charge dominated regimes. We present results of basic centroid-motion characterization, including measurements of closed-orbit distortion, momentum compaction factor, and natural chromaticity and dispersion. These are compared with results from computer simulations employing the code ELEGANT. We discuss the techniques and challenges behind the measurements with fast beam-position and wall-current monitors, and also the special role of the background ambient magnetic field for beam steering.
PSI, Villigen
LANL, Los Alamos, New Mexico
CIAE, Beijing
OPAL (Object Oriented Parallel Accelerator Library) is a tool for charged-particle optics in accelerator structures and beam lines including 3D space charge, short range wake-fields and a 1D coherent synchrotron radiation. Built from first principles as a parallel application, OPAL admits simulations of any scale, from the laptop to the largest HPC clusters available today. Simulations, in particular HPC (High Performance Computing) simulations, form the third pillar of science, complementing theory and experiment. In this paper we present numerical and HPC capabilities such as fast direct and iterative solvers together with timings up to several thousands of processors. The application of OPAL to our PSI-XFEL project as well as to the ongoing high power cyclotron upgrade will demonstrate OPAL's capabilities applied to ongoing projects at PSI. Plans for future developments will be discussed.
SLAC, Menlo Park, California
BNL, Upton, Long Island, New York
Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.
SLAC's Advanced Computations Department (ACD) has developed the parallel 3D Finite Element electromagnetic Particle-In-Cell code Pic3P. Designed for simulations of beam-cavity interactions dominated by space charge effects, Pic3P solves the complete set of Maxwell-Lorentz equations self-consistently and includes space-charge, retardation and boundary effects from first principles. Higher-order Finite Element methods with adaptive refinement on conformal unstructured meshes lead to highly efficient use of computational resources. Massively parallel processing with dynamic load balancing enables large-scale modeling of photoinjectors with unprecedented accuracy, aiding the design and operation of next-generation accelerator facilities. Applications include the LCLS RF gun and the BNL polarized SRF gun.
TRIUMF, Vancouver
CERN, Geneva
The simulation code COMBI has been developed to enable the study of coherent beam-beam effects in the full collision scenario of the LHC, with multiple bunches interacting at multiple crossing points over many turns. The parallel version of COMBI was first implemented using a soft-Gaussian collision model which entails minimal communication between worker processes. Recently we have extended the code to a fully self-consistent collision model using a Grid-Multipole method, which allows worker processes to exchange charge and field information in a compact form which minimizes communication overhead. In this paper we describe the Grid-Multipole technique used and its adaptation to the parallel environment through pre- and post-processing of charge and grid data. Performance measurements in multi-core and Myrinet-cluster environments will be given. We will also present our estimates of the potential for very large-scale simulations on massively-parallel hardware, in which the number of simulated bunches ultimately approaches the actual LHC bunch population.
TRIUMF, Vancouver
DAE/VECC, Calcutta
SFU, Burnaby, BC
ANL, Argonne
The TRIUMF ARIEL Project plans to build a 50MeV electron linac at 10mA to produce radioactive ion beams through photofission. Beam dynamics studies of the accelerator are on-going. The TRACK code originally written to simulate proton and heavy ion linacs has been used in e-linac modeling studies. This paper will summarize the TRACK simulation studies and the simulation results will be compared with other codes like PARMELA and ASTRA.
TUE, Eindhoven
Pulsar Physics, Eindhoven
The General Particle Tracer (GPT) code is a well established package for the design of charged particle accelerators and beam lines. A crucial component of this code is the calculation of Coulomb interactions. In this contribution we present two different numerical algorithms for the calculation of these particle-particle effects: The standard Particle-In-Cell (PIC) method and a Barnes-Hut (B&H) treecode approach. The PIC method is fast and reliable, but it does not include binary interactions. The method is therefore inapplicable when disorder induced heating plays a role, for example in electron microscopes and focused ion beams. The Barnes-Hut method, borrowed from the astrophysics community, calculates all pair wise interactions in an efficient manner. This approach covers all Coulomb effects, but it is potentially much slower. A realistic test case is presented highlighting the strengths and weaknesses of both approaches.
UMD, College Park, Maryland
Funding: Office of High Energy Physics, US Department of Energy (DoE).
Multipactor (MP) may occur in many situations: one- and two-surface MP, resonant and poly-phase-MP, on the surface of metals and dielectrics etc. We consider this phenomenon in dielectric loaded accelerator (DLA) structures. The starting point for our work is experimental and theoretical studies of such structures jointly done by Argonne National Lab and Naval Research Lab*. In the theoretical model developed during those studies, the space charge field due to the accumulated charged particles is taken into account as a parameter. We offer a non-stationary 2D cylindrical model where the DC field is taken into account self-consistently. We have improved our previous model** and demonstrated that its predictions are in good agreement with the results of other studies***. We also demonstrate some recent results where the effects of axial particle motion are taken into account.
*J.G. Power et al., PRL, 92, 164801, 2004
**O.V. Sinitsyn et. al., AIP Proc. 13th Advanced Accelerator Concepts, 2008
***J.G. Power, S.H. Gold, AIP Proc.12th Advanced Accelerator Concepts, 2006
BNL, Upton, Long Island, New York
NSCL, East Lansing, Michigan
CERN, Geneva
Studies of space charge effects in the Small Isochronous Ring (SIR) at Michigan State University revealed a fast longitudinal instability at and below the transition that could not be explained by the conventional negative mass instability. The observed beam behavior can be explained by the effect of the radial component of the coherent space charge force on the longitudinal motion. The transverse coherent space charge force effectively modifies the slip factor shifting the isochronous point and enhancing the negative mass instability. This paper presents results of numerical and experimental studies of the longitudinal beam dynamics in SIR and proposes an analytical model explaining the results.
EPFL, Lausanne
CERN, Geneva
A detailed knowledge of the beam coupling impedance of the CERN synchrotrons is required in order to identify the impact on instability thresholds of potential changes of beam parameters, as well as additions, removal or modifications of hardware. To this end, an update of the impedance database was performed, so that impedance results from theoretical calculations using new multilayer models, impedance results from electromagnetic field simulations and impedance results from bench measurements can be compiled. In particular, the impedance database is now set to separately produce the dipolar and quadrupolar transverse impedance and wakes that the HEADTAIL simulation code needs to accurately simulate the effect of the impedance on the beam dynamics.
CERN, Geneva
EPFL, Lausanne
The CERN PS crosses transition energy at about 6 GeV by using a second order gamma jump performed with special quadrupoles. However, for high-intensity beams, and in particular the single bunch beam for the neutron Time-of-Flight facility, a controlled longitudinal emittance blow-up is still needed to prevent a fast single-bunch vertical instability from developing near transition. A series of studies have been done in the PS in 2008 to measure the beam behaviour near transition energy for different settings of the gamma transition jump. The purpose of this paper is to compare those measurements with simulations results from the HEADTAIL code, which should allow to understand better the different mechanisms involved and maybe improve the transition crossing.
Fermilab, Batavia
Funding: work supported by the US Department of Energy
Stability issues of the mu2e proton beam are discussed. These include space-charge distortion of bunch shape, microwave instabilities, head-tail instabilities, as well as electron cloud effects.
Fermilab, Batavia
We examine the stability of intense flat bunches in barrier buckets. We consider a class of stationary distributions and derive analytical expressions for the threshold intensity at which Landau damping is lost against rigid dipole oscillations in the presence of impedances and space charge forces. Particle simulations are used to follow the dynamics in a barrier bucket and compare with the analytic expressions. These studies are related to experimental observations in the Recycler ring at Fermilab.
INFN/LNF, Frascati (Roma)
KEK, Ibaraki
Funding: Work supported in part by the “Ministero degli Affari Esteri, Direzione Generale per la Promozione e la Cooperazione Culturale”
A strong horizontal instability has been observed in the DAΦNE positron ring since 2003. Experimental observations suggest an electron cloud induced coupled bunch instability as a possible explanation. In this communication we present a simulation study of the electron cloud coupled bunch instability for the DAΦNE positron ring, performed with the code PEI-M, and compare the numerical results with experimental observations.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
KEK, Ibaraki
Kicker magnets are ones of dominant sources of impedances in the 3GeV Rapid Cycling Synchrotron (RCS) at Japan Proton Accelerator Research Complex (J-PARC). They may be limiting factors in achieving high intensity beams. Recently, the 300kW beam was accomplished at 3GeV RCS, while no instability was observed. In this paper, the space-charge effects are studied as beam stabilization effects.
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.
An L-band (1.3 GHz) sheet beam klystron that will nominally produce 10 MW, 1.6 ms pulses is being developed at SLAC for the ILC program. In recent particle-in-cell transport simulations of the 115 kV DC beam through the klystron buncher section without rf drive, a hose-type instability has been observed that is the result of beam noise excitation of transverse modes trapped between the rf cells. In this paper we describe analytical calculations and numerical simulations that were done to study the nature of this instability and explore the required mode damping and changes in the beam focusing to suppress it.
UMD, College Park, Maryland
Funding: This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office.
Beam centroid control is an important method for optimizing the performance for accelerators, including the University of Maryland Electron Ring (UMER), which is a scaled low-energy (10KeV) storage ring. The conventional response matrix and singular value decomposition approach do not work well on the UMER because of the unique ring structure. One of the purposes of this work is to verify that the beam centroid could be controlled in the presence of very strong space charge. In this paper, we present a novel algorithm which is based on the singular value decomposition, but uses a different response matrix, which is computed from the closed equilibrium orbit and beam positions up to the first four turns in the multi-turn beam circulation. Other issues like strong coupling between the horizontal steering dipoles and vertical steering dipoles in the beam injection section will be addressed. Implementation of this algorithm leads to significant improvement on the beam positions and multi-turn operation.
ORNL, Oak Ridge, Tennessee
GSI, Darmstadt
The 4ν=1 resonance of a linac is demonstrated when the depressed tune is around 90 deg. It is observed that this fourth order resonance is dominating over the better known envelope instability and practically replacing it. Simulation study shows a clear emittance growth by this resonance and its stopband. One of the authors [DJ] made a proposal to GSI to measure the stopband of this resonance. The experiment was conducted successfully and the experiment data will be presented separately in the conference.
Cockcroft Institute, Warrington, Cheshire
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
EMMA (Electron Machine with Many Applications) is a prototype non-scaling electron FFAG currently under construction at Daresbury Laboratory. The energy recovery linac prototype ALICE will operate as its injector, at a reduced the energy of 10 to 20 MeV, compared to its nominal energy of 35 MeV. An injection line has been designed which consists of a dogleg to extract the beam from ALICE, a matching section, a tomography section and some additional dipoles and quadrupoles to transport and match the beam to the entrance of EMMA. This injection line serves both as a diagnostic to measure the properties of the beam being injected into EMMA and also a useful diagnostic tool for ALICE operation. This paper details the simulations undertaken of the electron beam passing through the matching and tomography sections of the EMMA injection line, including the effect of space charge. This will be an issue in the energy range at which this diagnostic is being operated when combined with high bunch charge. A number of different scenarios have been modelled and an attempt made to compensate for the effects of space charge in the matching and tomography sections.
NSCL, East Lansing, Michigan
Cyclotron gas stopper is a newly proposed device to stop energetic ions in a high pressure helium gas and to transport them in a singly charged state with a gas jet to a vacuum region. Radioactive ions are slowed down by gas collisions inside the field of a weakly focusing cyclotron-type magnet and extracted via interaction with the Radio Frequency field of sequence of concentric electrodes (RF carpet). The present study focuses on a detailed understanding of space charge effects in the central ion extraction region. Such space charge effects originate from the ionization of the helium gas during the stopping of the ions and are the cause for beam rate limitations. Particle-in-cell simulation of two-component (electron-helium) plasma interacting via Coulomb forces were performed in a field created by ionized ions. Simulation results indicate beam rate capabilities and efficiencies far beyond those achieved with linear gas cells presently used to stop projectile fragments.