TEMF, Darmstadt
The Wien filter is well known as a common energy analyzer and is also used more and more as a compact variant of a spin rotator at low energy for electrons. The Wien filter based on a homogenous magnetic and electric field that are perpendicular to each other and transverse to the direction of the electrons. The rotation of the spin vector is caused by the magnetic field. If the force equilibrium condition is fulfilled the beam should not be deflected at the Wien filter. Simulations show that in the fringe fields the electrons get a kick. Therefore full 3D simulations of the electromagnetic fields and beam dynamics simulations are studied in detail at the example of the Wien filter at the new polarized 100 keV electron injector at the S-DALINAC. The results of the simulations with CST Design Environment(TM), MAFIA and V-Code are presented.
CERN, Geneva
Fermilab, Batavia, Illinois
Advanced Magnet Lab., Inc, Melbourne, Florida
This work is partially supported under U. S. Department of Energy grant : DoE SBIR DE-FG02-06ER 84492
PPPL, Princeton, New Jersey
The Paul Trap Simulator Experiment 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 beam's frame-of-reference. The transverse dynamics of particles in both systems are described by the same sets of equations, including all nonlinear space-charge effects. The time-dependent quadrupolar electric fields created by the confinement electrodes of a linear Paul trap correspond to the axially-dependent magnetic fields applied in the AG system. Results are presented from experiments in which the lattice period and strength are changed over the course of the experiment to transversely compress a beam with an initial depressed-tune of 0.9. Instantaneous and smooth changes are considered. Emphasis is placed on determining the conditions that minimize the emittance growth and the number of halo particles produced after the beam compression. The results of PIC simulations performed with the WARP code agree well with the experimental data. Initial results from a newly installed laser-induced fluorescence diagnostic will also be discussed.
KEK, Ibaraki
[1] T. Ieiri et al., Proc. of EPAC06, Edinburgh, Scotland, 2101 (2006).
ISSP/SRL, Chiba
* J. M. Wang and J. Wu, PRST-AB 7, 034402(2004)
ALBA, Bellaterra (Cerdanyola del Valles)
LBNL, Berkeley, California
By "conditioning" an electron beam, through establishing a correlation between transverse action and energy within the beam, the performance of free electron lasers (FELs) can be dramatically improved. Under certain conditions, the FEL can perform as if the transverse emittances of the beam were substantially lower than the actual values. After a brief review of the benefits of beam conditioning, we present a method to generate this correlation through the use of a plasma channel. The strong transverse focusing produced by a dense plasma (near standard gas density) allows the optimal correlation to be achieved in a reasonable length channel, of order 1 m. This appears to be a convenient and practical method for achieving conditioned beams, especially in comparison with other methods which require either a long beamline or multiple passes through some type of ring.
Fermilab, Batavia, Illinois
The linear-field non-scaling FFAG lattices originally proposed for multi-GeV muon acceleration are now being modified for application to order 100 MeV/u proton or carbon medical applications. The momentum range is large and the chromatic tune variation is significant. In the medical case, the time of flight variation is immaterial but the issue of resonance crossing is more acute owing to the much lower rate of energy gain. Magnets with non-normal entry/exit faces are considered as means to reduce the tune variation. Thus one is motivated to study fringe fields and their effects. We make a brief study of dipole and quadrupole magnets with normal and rotated entry/exit faces. For the artificial case of a cosine-squared fall off in the quadrupole field, analytic results are obtained which though approximate are superior to numerical integration. This property is achieved by insisting that the error in the equation of motion is zero and the determinant is unity at the entry, exit and centre of the fringe field.
Linear-field non-scaling FFAGs are proposed for multi-GeV muon acceleration and order hundred MeV/u proton or carbon medical applications. The periodic lattices, which have large momentum acceptance (factor >3), employ cells comprised of combined function magnets. In one implementation, rectangular-shaped quadrupoles are used, with the dipole component generated by off-setting the magnet centre. This feature, coupled with the large radial aperture, gives rise to orbits with large displacement and/or divergence from the quadrupole centre. The angles may be so large that there is a partial interchange of longitudinal and radial momenta. We examine two methods to devise maps (through the body field) that are third order in radial coordinate and higher order in momentum. The WKBJ approximation is concluded to be no better than the usual linear transfer matrix. A Green's function approach is carried through to non-linear mappings for the dynamical variables, which are coupled. The first partial derivative of this map (relates to tune variation) produces a linear transfer matrix which must have unity determinant. For the FFAG application, the map is comparable with numerical integration.
IAP, Frankfurt am Main
FZJ, Julich
INFN-Ferrara, Ferrara
* Conceptual Design Report for an International Facility for Antiprotonand Ion Research, www.gsi.de/GSI-future/cdr.** PAX Technical Proposal, www.fz-juelich.de/ikp/pax.
MEPhI, Moscow
NSCL, East Lansing, Michigan
LLNL, Livermore, California
An investigation is being made into the feasibility of making a compact proton accelerator for medical radiation treatment. The accelerator is based on high gradient insulation (HGI) technology. The beam energy should be tunable between 70 and 250 MeV to allow the Bragg peak to address tumors at different depths in the patient. The desired radiation dose is consistent with a beam charge of 40 pico-coulombs. The particle source is a small 2 mm plasma device from which a several nano-second pulse can be extracted. The beam current is selectable by the potential of the extraction electrode and is adjustable in the range of 10-100 milli-Amperes. This beam is then accelerated and focused by the next three electrodes forming a Accel-Deaccel-Accel (ADA) structure leading to the DWA accelerator block. The spot size is adjustable over 2 to 10 mm. A transparent grid terminates the injector section and prevents the very high gradient of the HGI structure from influencing the overall focusing of the system. The beam energy is determined by the length of the DWA structure that is charged. This give independent selection of beam dose, size and energy.
LLNL, Livermore, California
The dielectric wall accelerator (DWA) is a compact induction accelerator structure that incorporates the accelerating mechanism, pulse forming structure, and switch structure into an integrated module. The DWA consists of stacked stripline Blumlein assemblies, which can provide accelerating gradients in excess of 100 MeV/meter. Blumleins are switched sequentially according to a prescribed acceleration schedule to maintain synchronism with the proton bunch as it accelerates. A finite difference time domain code (FDTD) is used to determine the applied acceleration field to the proton bunch. Particle simulations are used to model the injector as well as the accelerator stack to determine the proton bunch energy distribution, both longitudinal and transverse dynamic focusing, and emittance associated with various DWA configurations.
UCLA, Los Angeles, California
Fermilab, Batavia, Illinois
Rochester University, Rochester, New York
Northern Illinois University, DeKalb, Illinois
Focusing of a 15 MeV, 19 nC electron bunch by an underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated in experiments at the Fermilab NICADD Photoinjector Laboratory (FNPL). The strong 1.9 cm focal-length plasma-lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam-envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Correlations between the beam charge and the properties of the beam focus corroborate this conclusion. Time resolved measurements of the focused electron bunch are also reported and all results are compared to simulations.
LLNL, Livermore, California
LBNL, Berkeley, California
PPPL, Princeton, New Jersey
Voss Scientific, Albuquerque, New Mexico
Intense heavy ion beam pulses need to be compressed in both the transverse and longitudinal directions for warm dense matter and heavy ion fusion applications. Previous experiments and simulations utilized a drift region filled with high-density plasma in order to neutralize the space-charge and current of a 300 keV K+ beam, and achieved transverse and longitudinal focusing separately to a radius < 2 mm and pulse width < 5 ns, respectively. To achieve simultaneous beam compression, a strong solenoid is employed near the end of the drift region in order to transversely focus the beam to the longitudinal focal plane. Simulations of near-term experiments predict that the ion beam can be focused to a sub-mm spot size coincident with the longitudinal focal plane, reaching a peak beam density in the range 1012 - 1013 cm-3, provided that the plasma density is large enough for adequate neutralization. Optimizing the compression under the appropriate experimental constraints offers the potential of delivering higher intensity per unit length of accelerator to the target, thereby allowing more compact and cost-effective accelerators and transport lines to be used as ion beam drivers.
PAL, Pohang, Kyungbuk
RIST, Pohang
Pohang Accelerator Laboratory has studied SRF cavity and set up SRF test laboratory from January 2006. The first activity for SRF research was to develop SRF 3rd harmonic cavity for Pohang Light Source, which was designed, fabricated and tested in 2006. The cryostat are under design. The fabrication of ICHIRO cavity, which is ILC ACD cavity, is PAL's second activity related to SRF. Deep drawing, trimming and welding by electron beam for a 9-cell ICHIRO cavity were done in PAL. The polishing processes for the RF surface including electropolishing were done in KEK under the collaboration between two institutes. This will be tested with real beam in STF-1 of KEK in second half period of 2007. This paper reports the results of fabrication of ICHIRO single- and nine-cell cavities performed in PAL.
Fermilab, Batavia, Illinois
The proposed High Intensity Neutrino Source at Fermilab is based on an 8 GeV linear proton accelerator which consists of a normal-conducting and a superconducting section. The normal-conducting (warm) section is composed of an ion source, a radio frequency quadrupole, a medium energy beam transport and 16 normal-conducting crossbar H-type cavities that accelerate the beam from 2.5 MeV to 10 MeV (from β=0.0744 to β=0.1422). These warm cavities are separated by superconducting solenoids enclosed in individual cryostats. Beyond 10 MeV, the design uses superconducting spoke resonators to accelerate the beam up to 8 GeV. In this paper, we illustrate the completion of the first normal-conducting crossbar h-type cavity (β=0.0744) explaining in detail the mechanical engineering aspects related to the machining and brazing processes. The radio-frequency measurements and tuning performed at Fermilab on the resonator and the comparisons with the former simulations are also discussed.
MIT/PSFC, Cambridge, Massachusetts
A concept for a high-power ribbon-beam klystron (RBK) employing a novel large-aspect ratio elliptic electron beam instead of a conventional circular electron beam is presented. Both cold-fluid and kinetic equilibrium theories are developed and applied in the design of the elliptic electron beam for the RBK. A small-signal theory is developed and applied in the design of the beam tunnel and the input, idler and output cavities. The electron gun and beam matching is being studied. Design results of a 10 MW 1.3 GHz RBK for the International Linear Collider (ILC) and of a 50 MW 22 GHz RBK for high-gradient research will be discussed.
INFN - Gruppo Messina, S. Agata, Messina
Universita di Messina, Messina
POSTECH, Pohang, Kyungbuk
PAL, Pohang, Kyungbuk
An intense L-band electron accelerator is now being installed at PAL (Pohang Accelerator Laboratory) for initial tests. It is capable of producing 10-MeV electron beams with average 30 kW. This accelerator has a diode-type E-gun, a pre-buncher cavity, and an accelerating column with the built-in bunching section. We conduct simulational study for the commissioning scenario by the PARMELA code. At first, we observe the beam position and the beam current when the beam line is misaligned under no fields. Next, turning on focusing solenoids we observe the beam position change to check the alignments of the solenoids. Finally, varying RF power and phase of the pre-buncher we observe beam energy and beam power to obtain the optimum pre-buncher condition. In this paper, we present simulational results for each step. We also present commissioning strategies based on these results.
TRIUMF, Vancouver
Fixed Field Alternating Gradient (FFAG) machines have been the subject of recent international activity due to their potential for medical applications and accelerator-based technologies. In particular, nonscaling FFAGs (where the optics are not constant and therefore do not scale with momentum) stand to offer the high current advantage of the cyclotron combined with the smaller radial aperture of the synchrotron plus variable extraction energy. Here, a hybrid design for a nonscaling FFAG accelerator has been invented which uses both edge and alternating-gradient focusing principles applied to a combined-function magnet applied in a specific configuration to stabilize tunes through an acceleration cycle which extends over a factor of 2-6 in momentum. Using normal conducting magnets, the final, extracted energy from this machine attains 400 MeV/nucleon and a normalized emittance of ~10 - 20π, and thus supports a carbon ion beam in the energy range of interest for cancer therapy.
MIT/PSFC, Cambridge, Massachusetts
A theory is presented for the design of an ideal non-relativistic circular beam system including a charged-particle emitting diode, a diode aperture, a circular beam tunnel, and a focusing magnetic field that matches the beam from the emitter to the beam tunnel. The magnetic field is determined by balancing the forces throughout the gun and transport sections of the beam system. OMNITRAK simulations are performed, validating theory. As applications, a circular electron beam system is discussed for space-charge-dominated beam experiments such as the University of Maryland Electron Ring (UMER), and a circular ion beam system is discussed for high energy density physics (HEDP) research.
LLNL, Livermore, California
As part of the ongoing development of fast neutron imaging technology for national secu-rity applications at LLNL, a large-format imaging optics system has been designed and built. The system will be used to acquire radiographic images of heavily-shielded low-Z objects irradiated by ~ 10 MeV neutrons and is expected to have an ultimate spatial resolution ~ 1 mm (FWHM). It is comprised of a 65 cm x 65 cm plastic scintillator (e.g. BC-408), an aluminized front-surface turning mirror and a fast (~ f/1.25) optical lens coupled to a CCD camera body with a cryo-cooled, back-illuminated 4096 x 4096 (15 micron) pixel sensor. The lens and camera were developed and purchased from vendors and system integration was done at LLNL. A description of the overall system and its initial performance characteristics shall be presented.
RadiaBeam, Los Angeles, California
UCLA, Los Angeles, California
The fixed-field alternating-gradient (FFAG) betatron has emerged as a viable alternative to RF linacs as a source of high-energy radiation for industrial and security applications. For industrial applications, high average currents at modest relativistic electron beam energies, typically in the 5 to 10 MeV range, are desired for medical product sterilization, food irradiation and materials processing. For security applications, high power x-rays in the 3 to 20 MeV range are needed for rapid screening of cargo containers and vehicles. In a FFAG betatron, high-power output is possible due to high duty factor and fast acceleration cycle: electrons are injected and accelerated in a quasi-CW mode while being confined and focused in the fixed-field alternating-gradient lattice. The beam is accelerated via magnetic induction from a betatron core made with modern low-loss magnetic materials. Here we present the design and status of a prototype FFAG betatron, called the Radiatron, as well as future prospects for these machines.
USC, Los Angeles, California
UCLA, Los Angeles, California
Simulation and analysis of the ion motion and multiple ionization in a plasma wakefield accelerator is presented for the parameters required of a future ILC afterburner. We show that although ion motion leads to substantial emittance growth for extreme parameters of future colliders in the sub-micron spot size regime, several factors that can mitigate the effect are explored. These include sunchrotron damping, plasma density gradient and hot plasma.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
Systematic measurements of energy gain as a function of plasma parameters in the SLAC electron beam-driven plasma wakefield acceleration (PWFA) experiments lead to very important understanding of the beam-plasma interaction. In particular, measurements as a function of the plasma length Lp show that the energy gain increases linearly with Lp in the 10 to 30 cm range. Based on this scaling, the plasma was subsequently lengthened to Lp=90cm, resulting in the first demonstration of the doubling of the energy of a fraction of the incoming 42GeV electrons*. The peak accelerating gradient is larger than 40GV/m and is sustained over meter-scale plasma lengths. These measurements also reveal that the optimum plasma density for acceleration is about 2.7·1017/cc, larger than the value predicted by the linear theory for the approximately 20 microns bunch length, confirming that the experiment is conducted in the non-linear regime of the PWFA. Detailed experimental results will be presented.
* "Energy doubling of 42 GeV electrons in a meter scale plasma wakefield accelerator", I. Blumenfeld et. al., Nature, 2006, accepted
SLAC, Menlo Park, California
The main linac of the International Linear Collider (ILC) accelerates short, high peak current bunches into the Beam Deliver System (BDS) on the way to the interaction point. In the BDS wakefields are excited by the resistance of the beam pipe walls and by beam pipe transitions that will tend to degrade the emittance of the beam bunches. In this report we calculate the effect on emittance of incoming jitter or drift, and of misalignments of the beam pipes with respect to the beam axis, both analytically and through multi-particle tracking. Finally, we discuss ways of ameliorating the wake effects in the BDS.
UCLA, Los Angeles, California
*R. Yoder and J. Rosenzweig, Phys. Rev. STAB 8, 111301 (2005); Z. Zhang et al., Phys. Rev. STAB 8, 071302 (2005); A. Mizrahi and L. Schachter, Phys. Rev. E 70, 016505 (2004).
BNL, Upton, Long Island, New York
University of California IIrvine, Irvine, California
Muons, Inc, Batavia
UCI, Irvine, California
Plasma lens concept is examined as an alternative to focusing horns and solenoids for a neutrino beam facility. The concept is based on a combined high-current lens/target configuration. Current is fed at an electrode located downstream from the beginning of the target where pion capturing is needed. Some of the current flows through the target, while the rest is carried by plasma outside the target. A second plasma lens section, with an additional current feed, follows the target. Plasma of this section is immersed in a solenoidal magnetic field to facilitate its current profile shaping to optimize pion capture. Simulation of the second section alone yielded a 10% higher neutrino production than the horn system. Plasma lenses have additional advantages: larger axial currents, high signal purity: minimal neutrino background in anti-neutrino runs. Lens medium consists of plasma, consequently, particle absorption and scattering is negligible. Withstanding high mechanical and thermal stresses is not an issue. Results of capturing and focusing obtained for various plasma lens configurations will be presented.
IF-UFRGS, Porto Alegre
The goal of this work is to analyze the envelope dynamics of magnetically focused and high-intensity charged particle beams. As known, beams with mismatched envelopes decay into its equilibrium state with a simultaneous increasing of emittance. This emittance growth implies that, in the stationary regime, the transverse phase-space of the beam is characterized by a tenuous population of hot particles around a dense population of cold particles. To describe this emittance growth, it was used the test-particle approach for the development of a simplified self-consistent macroscopic model, whose self-consistency is a result of the inclusion of the emittance growth into the envelope equation. The model is then compared with full N-particle beam simulations and the agreement is shown to be quite reasonable. The model revealed to be useful to understand the physical aspects of the problem and is computationally faster when compared with full simulations.
IF-UFRGS, Porto Alegre
We start by analyzing the image effects of a cylindrical conducting pipe on a continuous beam with elliptical symmetry. In particular, we derive an exact expression for the self-field potential of the beam inside the pipe without using any sort of multipole expansion. By means of a variational method, the potential for beams with varying density profiles along an elliptical shape is used to search for equilibrium solutions for intense beams. For that, we assume a uniform focusing in the smooth-focusing approximation. A curious result is that the product of the rms sizes along the ellipsis semi-axis stays constant as the pipe radius is varied. Finally, we prove that despite the nonlinear forces imposed by the image charges of an arbitrary shape conducting pipe, intense beams in uniform focusing fields preserve a uniform density in the equilibrium.
TRIUMF, Vancouver
The Enge function can be used to parametrize any element with well-defined edges. If an element is too short, however, there is no unambiguous definition of the effective edge. We first demonstrate that very little fringe field detail is needed to obtain accurate maps even up to fifth order. Then we go on to show a simple fitting algorithm that works well for short as well as long quadrupoles. The results are true whether the quads are magnetic or electrostatic.
GSI, Darmstadt
IUCF, Bloomington, Indiana
TIT, Yokohama
Utsunomiya University, Utsunomiya
For researches in high energy density physics and inertial confinement fusion by using heavy ion beams, high-current beam dynamics should be understood well. The heavy ion beam is longitudinally compressed by a head-to-tail velocity tilt applied from high-power induction voltage modules. In this study, emittance growth due to the longitudinal bunch compression is numerically investigated by using a particle-in-cell simulation. The code developed is dealt with three dimensional particle motions, and 2D transverse electric field is solved by Poisson equation coupled with 1D longitudinal electric field. We indicate the particle dynamics due to the non-linear longitudinal-transverse coupling effect around the stagnation point in the longitudinal compression.
HUST, Wuhan
An intelligent magnet design, modelling and optimization method with the aid of beam dynamics analysis and three dimensional magnetic field calculation is introduced. The whole procedure is implemented in an integrated virtual prototyping environment built with python language. As a case study, the main magnet design of a 16MeV H- compact cyclotron is illustrated. Both the field isochronism and transversal focusing of the beam can be fulfilled, and the mechanical analysis is performed to validate the feasibility in mechanics.
BINP SB RAS, Novosibirsk
IC SB RAS, Novosibrsk
ICM&MG SB RAS, Novosibirsk
LBNL, Berkeley, California
PSI, Villigen
LBNL, Berkeley, California
PPPL, Princeton, New Jersey
Voss Scientific, Albuquerque, New Mexico
Longitudinal bunching factors in excess of 70 of a 300-keV, 27-mA K+ ion beam have been demonstrated in the Neutralized Drift Compression Experiment in rough agreement with LSP particle-in-cell end-to-end simulations. These simulations include both the experimental diode voltage and induction bunching module voltage waveforms in order to specify the initial beam longitudinal phase space critical to longitudinal compression. To maximize simultaneous longitudinal and transverse compression, we designed a solenoidal focusing system that compensated for the impact of the applied velocity tilt on the transverse phase space of the beam. Here, pre-formed plasma provides beam neutralization in the last one meter drift region where the beam perveance becomes large. Integrated LSP simulations, that include detailed modeling of the diode, magnetic transport, induction bunching module, plasma neutralized transport, were critical to understanding the interplay between the various accelerator components. Here, we compare simulation results with the experiment and discuss the contributions to longitudinal and transverse emittance that limit compression.
BNL, Upton, Long Island, New York
Fermilab, Batavia, Illinois
For muons with preferable for ionization cooling momentum <300MeV/c the longitudinal motion is naturally undamped. In order to provide the longitudinal damping a correlation between muon momentum and transverse position - described in terms of the dispersion function - should be introduced. In the present report we consider the possibility of dispersion generation in a periodic sequence of alternating solenoids (FOFO channel) by choosing the tune in the second passband (i.e. above half-integer per cell) and tilting the solenoids in adjacent cells in the opposite direction. Analytical estimates as well as simulation results for equilibrium emittances and cooling rates are presented.
LLNL, Livermore, California
The Kapchinskij-Vladimirskij equations describe the evolution of the beam envelopes in a periodic system of quadrupole focusing cells and are widely used to help predict the performance of such systems. Being nonlinear, they are usually solved by numerical integration. There have been numerous papers describing approximate solutions with varying degrees of accuracy. We have found an exact solution for a matched beam in the limit of zero space charge. The model is FODO with a full occupancy, piecewise-constant focusing function. Our explicit result for the envelope a(z) is exact for phase advances up to 180 degrees and all other values except multiples of 180 degrees. The peak envelope size is minimized at 90 degrees. The higher stable bands require larger, very accurate, field strengths while producing significantly larger envelope excursions.
PPPL, Princeton, New Jersey
UCB, Berkeley, California
LBNL, Berkeley, California
Voss Scientific, Albuquerque, New Mexico
Future warm dense matter experiments with space-charge dominated ion beams require simultaneous longitudinal bunching and transverse focusing. The challenge is to longitudinally bunch the beam two orders of magnitude to a pulse length shorter than the target disassembly time and focus the beam transversely to a sub-mm focal spot. An experiment to simultaneously focus a singly charged potassium ion beam has been carried out at LBNL. The space charge of the beam must be neutralized so only emittance limits the simultaneous focusing. An induction bunching module provides a head-to-tail velocity ramp upstream of a plasma filled drift section. Tuning the initial beam envelope to compensate for the defocusing of the bunching module enables simultaneous focusing. A comparison of experimental and calculated results are presented, including the transverse distribution and the longitudinal phase-space of the beam.
LLNL, Livermore, California
LBNL, Berkeley, California
PPPL, Princeton, New Jersey
UCB, Berkeley, California
Voss Scientific, Albuquerque, New Mexico
This work was supported by the Office of Fusion Energy Sciences, of the U. S. Department of Energy under Contract No. DE-AC02-05CH11231, W-7405-Eng-48, DE-AC02-76CH3073 for HIFS-VNL.
LANL, Los Alamos, New Mexico
Lehigh University, Bethlehem, Pennsylvania
MIT/PSFC, Cambridge, Massachusetts
A warm-fluid theory of a thermal equilibrium for a rotating charged particle beam in a periodic solenoidal focusing magnetic field is presented. The warm-fluid equilibrium equations are solved in the paraxial approximation. It is shown that the flow velocity for the thermal equilibrium corresponds to periodic rigid rotation and radial pulsation. The equation of state for the thermal equilibrium is adiabatic. The beam envelope equation and self-consistent Poisson's equation are derived. The numerical algorithm for solving self-consistent Poisson's equation is discussed. Density profiles are calculated numerically for high-intensity beams. Temperature effects in such beams are investigated, and the validity of the warm-fluid theory is discussed. Examples of electron and ion beams are presented for space-charge-dominated beam and high energy density physics (HEDP) research.
UMD, College Park, Maryland
This paper describes the longitudinal expansion of a 10 keV, 100 mA electron beam in the University of Maryland Electron Ring. The expansion of the beam tail was found to be sensitive to the choice of transverse focusing settings due to the presence of an abnormality in the beam current profile. Expansion of the beam head, where no abnormality was observed, is in good agreement with the one-dimensional cold fluid model.
A novel 3D method of sheet beam (SB) gun design has recently been developed. Second order ruled surfaces (SORS) to define the geometry of the gun electrodes. The gun design process is made simpler if SORS are derived from simple analytical formulas. The coefficients of the mathematical expression are parameters that set the gun optic. A proposed design method is discussed and illustrated.
A classical electron/positron accelerating structure is a disk loaded cylindrical waveguide. The accelerator structure here has azimuth symmetry. The proposed structure contains a disk-loaded cylindrical waveguide where there is a periodical change of rf-field vs. azimuth. The modulation deforms the rf-field in such a manner that the accelerated particles undergo transverse focusing forces. The new class of accelerator structures covers the initial part of e+/e- linacs where a bunch is not rigid and additional transverse focusing fields are necessary. We discuss a bunch formation with a high transverse aspect ratio in the proposed structure and particularly in the photoinjector part of a linac.
Jefferson Lab, Newport News, Virginia
The CEBAF recirculating accelerator consists of two CW superconducting RF linacs, through which an electron beam is accelerated for up to 5 passes. Focusing and steering elements affect each pass differently, requiring a multipass steering protocol to correct the orbits. Perturbations include lens misalignments (including long-term ground motion), BPM offsets, and focusing and steering from RF fields inside the cavities. A previous treatment of this problem assumed all perturbations were localized at the quadrupoles and the absence of x-y coupling. Having analyzed the problem and characterized the solutions, we developed an empirical iterative protocol to compare against previous results in the presence of skew fields and cross-plane coupling. We plan to characterize static and acceleration-dependent components of the beam line perturbations to allow systematic and rapid configuration of the accelerator at different linac energy gains.
PPPL, Princeton, New Jersey
The transverse compression and dynamics of intense charged particle beams, propagating through a periodic quadrupole lattice, play an important role in many accelerator physics applications. Typically, the compression can be achieved by means of increasing the focusing strength of the lattice along the beam propagation direction. However, beam propagation through the lattice transition region inevitably leads to a certain level of beam mismatch and halo formation. In this paper we present a detailed analysis of these phenomena using particle-in-cell (PIC) numerical simulations performed with the WARP code. A new definition of beam halo is proposed in this work that provides the opportunity to carry out a quantitative analysis of halo production by a beam mismatch.
PPPL, Princeton, New Jersey
LBNL, Berkeley, California
Plasmas are sources of electrons for charge neutralizing ion beams to allow them to focus to small spot sizes and compress their axial pulse length. Sources must operate at low pressures and without strong electric/magnetic fields. To produce meter-long plasmas, sources based on ferroelectric ceramics with large dielectric coefficients were developed. The sources use BaTiO3 ceramic to form plasma. The drift tube inner wall of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic and ~7 kV is applied across the wall of the ceramics. A 20-cm-long prototype source produced plasma densities of 5·1011 cm-3. It was integrated into the Neutralized Transport Experiment and successfully neutralized the K+ beam. A one-meter-long source comprised of five 20-cm-long sources has been tested and characterized, producing relatively uniform plasma over the length of the source in the 1·1010 cm-3 range. This source was integrated into NDCX for beam compression experiments. Experiments with this source yielded compression ratios ~80. Future work will consider longer and higher plasma density sources to support beam compression and high energy density experiments.
PPPL, Princeton, New Jersey
Background plasma can be used as a convenient tool for manipulating intense charge particle beams, for example, for ballistic focusing and steering, because the plasma can effectively reduce the space-charge potential and self-magnetic field of the beam pulse. We previously developed a reduced analytical model of beam charge and current neutralization for an ion beam pulse propagating in a cold background plasma. The reduced-fluid description provides an important benchmark for numerical codes and yields useful scaling relations for different beam and plasma parameters. This model has been extended to include the additional effects of a solenoidal magnetic field and gas ionization. Analytical studies show that a sufficiently large solenoidal magnetic field can increase the degree of current neutralization of the ion beam pulse. The linear system of equations has been solved analytically in Fourier space. For a strong enough applied magnetic field, poles emerge in Fourier space. These poles are an indication that whistler waves and lower hybrid waves are excited by the beam pulse.
BNL, Upton, Long Island, New York
Electron cooling at RHIC-II upgrade imposes strict requirements on the quality of the electron beam at the cooling section. Beam current dependent effects such as the space charge, wake fields, CSR in bending magnets, trapped ions, etc., will tend to spoil the beam quality and decrease the cooling efficiency. In this paper, we estimate the defocusing effect of the space charge at the cooling section and describe our plan to compensate the defocusing space charge force by focusing solenoids. We also estimate the energy spread and emittance growth cased by wake fields. Finally, we discuss ion trapping in the electron cooler and consider different techniques to minimize the effect of ion trapping.
The ILC Linac Group at SLAC is actively pursuing a broad range of R&D to improve the reliability and reduce the cost of the L-band (1.3 GHz) rf system and normal-conducting accelerators. Current activities include the development of a Marx-style modulator and a 10 MW sheet-beam klystron, operation of an L-band (1.3 GHz) rf source using an SNS HVCM modulator and commercial klystron, construction of an rf distribution system with adjustable power tap-offs and custom hybrids, tests of cavity coupler components to understand rf processing limitations, simulation of multipacting in the couplers, optimization of the cavity fill parameters for operation with a large spread in sustainable cavity gradients and operation of a 5-cell prototype positron capture cavity. This paper surveys the results from the past year and reviews L-band R&D at other labs, in particular, that at DESY for the XFEL project.
LANL, Los Alamos, New Mexico
IF-UFRGS, Porto Alegre
This paper analyzes the combined envelope-centroid dynamics of magnetically focused high-intensity charged beams surrounded by conducting walls. Similarly to the case were conducting walls are absent, we show that the envelope and centroid dynamics decouples from each other. Mismatched envelopes still decay into equilibrium with simultaneous emittance growth, but the centroid keeps oscillating with no appreciable energy loss. Some estimates are performed to analytically obtain some characteristics of halo formation seen in the full simulations.
IF-UFRGS, Porto Alegre
We analyze the dynamics of inhomogeneous, magnetically focused high-intensity beams of charged particles. While for homogeneous beams the whole system oscillates with a single frequency, any inhomogeneity leads to propagating transverse density waves which eventually result in a singular density build up, causing wave breaking and jet formation. The theory presented in this paper allows to analytically calculate the time at which the wave breaking takes place. It also gives a good estimate of the time necessary for the beam to relax into the final stationary state consisting of a cold core surrounded by a halo of highly energetic particles.
DESY, Hamburg
FZD, Dresden
Northern Illinois University, DeKalb, Illinois
We undertake a study of particle dynamics in a model fixed-field alternating-gradient (FFAG) synchrotron in which space-charge plays a central role. The space-charge force corresponds to a Gaussian charge distribution in both transverse dimensions. The betatron-tune is linearly ramped through resonance. This ramping alone can cause particles to enter orbits that have chaotic motion.. We found that space-charge can lead to spreading of the available tunes which can either increase or decrease the effects of resonance. By applying recently developed techniques to measure complexity in the orbital dynamics, we also determine whether chaoticity can arise in particle trajectories and subsequently influence resonance crossings. Furthermore, we can see that the chaoticity changes drastically in the area around a resonance crossing.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
Recent electron beam driven plasma wakefield accelerator experiments carried out at SLAC showed trapping of plasma electrons. These trapped electrons appeared on an energy spectrometer with smaller transverse size than the beam driving the wake. A connection is made between transverse size and emittance; due to the spectrometer?s resolution, this connection allows for placing an upper limit on the trapped electron emittance. The upper limit for the lowest normalized emittance measured in the experiment is 1 mm∙mrad.
Based on numerical solution of the Fokker-Plank Equation we study the effect of longitudinal damping on the modulation of the bunch length in a storage ring with high RF voltage and momentum compaction
SLAC, Menlo Park, California
Jefferson Lab, Newport News, Virginia
For accelerator projects with ultra short electron beam, beam dynamics study has to invoke the short-range wakefield. In this paper, we first obtain the short-range dipole mode resistive wall wakefield. Analytical approach is then developed to study the single bunch transverse beam dynamics due to this short-range resistive wall wake. The results are applied to the LCLS undulator and some other proposed accelerators.
SLAC, Menlo Park, California
In this paper, we study the single bunch transverse beam dynamics in the presence of random displacements of resistive wall segments and focusing elements. Analytical formulas are obtained for long-range resistive wall wake, together with numerical results for short-range resistive wall wake. Tolerances on this random displacement are studied regarding to emittance growth and phase slippage in an undulator. The results are applied to the LCLS project and some other proposed accelerators.