FPAP  —  Two-Stream Instabilities and Collective Feedback   (20-May-05   08:30—12:20)

Paper Title Page
FPAP001 Electron Cloud Build-Up Study for DAFNE 779
 
  • C. Vaccarezza, R. Cimino, A. Drago, M. Zobov
    INFN/LNF, Frascati (Roma)
  • G. Bellodi
    CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon
  • K. Ohmi
    KEK, Ibaraki
  • M.T.F. Pivi
    SLAC, Menlo Park, California
  • G. Rumolo
    GSI, Darmstadt
  • D. Schulte, F. Zimmermann
    CERN, Geneva
 
  After the first experimental observations compatible with the presence of the electron cloud effect in the DAFNE positron ring, a more systematic study has been performed regarding the e-cloud build-up and related instability. The measured field map of the magnetic field has been taken into account in the simulation for elements present in the four 10 m long bending sections, representing 40% of the whole positron ring. The simulation results obtained with different codes are presented and compared with the recent experimental observations performed on the beam instabilities and the vacuum behavior of the positron ring.  
FPAP002 Experimental Determination of E-Cloud Simulation Input Parameters for DAFNE 817
 
  • C. Vaccarezza, R. Cimino
    INFN/LNF, Frascati (Roma)
  • A. Giglia, N. Mahne
    ELETTRA, Basovizza, Trieste
  • S. Nannarone
    UNIMORE, Modena
 
  After the first experimental observations compatible with the presence of the electron-cloud effect in the DAFNE positron ring, an experimental campaign has been started to measure realistic parameters to be used in the simulation codes. Here we present a synchrotron radiation experiment on the photon reflectivity from the actual Al vacuum chamber of DAFNE (same material, roughness and surface cleaning as the one used to manufacture the ring) in the same energy range of photons produced by the accelerator itself. The derived experimental parameter has than been included in the e-cloud simulation codes and the obtained results confirm the relevance of the detailed knowledge of the input parameter to obtain reliable e-cloud simulations.  
FPAP003 Simulation Study of the Electron Cloud Instability in SuperKEKB 868
 
  • H. Fukuma
    KEK, Ibaraki
  • L. Wang
    BNL, Upton, Long Island, New York
 
  The electron-cloud instability (ECI), especially a beam blowup caused by the single-bunch instability, is one of the most important issues faced at existing B factories. In SuperKEKB which is an upgrade plan of the KEK B factory, a positron beam will be stored in the high energy ring after LINAC upgrade to mitigate the ECI and ante-chambers will be effective to reduce the number of electrons. Nevertheless the ECI might be an issue of SuperKEKB because a large beam current of 4.1A will be stored with a short bunch spacing of 2ns. We performed a simulation of the cloud buildup by a program CLOUDLAND. The average electron density and the electron density at the center of a chamber were calculated both in drift space and in various magnetic fields. The result shows that a solenoid field is very effective for reducing the electron density. The simulated electron density will be compared with a threshold electron density of the strong head-tail instability.  
FPAP004 Simulation Analysis of Head-Tail Motion Caused by Electron Cloud 907
 
  • K. Ohmi, J.W. Flanagan, H. Fukuma, S. Hiramatsu, H. Ikeda, M. Tobiyama
    KEK, Ibaraki
  • E. Perevedentsev
    BINP SB RAS, Novosibirsk
 
  Synchro-beta side band caused by electron cloud instability has been observed at KEK-B factory. The side-band appears between $νβ+νs$ and $νβ+2νs$ above the threshold of beam size blow up and disappear by applying solenoid field. The side-band is an evidence of strong head-tail instability caused by electron cloud. The side-band is characterized by positive shift, $+1-2νs$, while general strong head-tail instabilities give frequency with negative shift $νbeta-ν_s$. We study the synchro-beta spectrum using a code, PEHTS, which simulates single bunch electron cloud instability.  
FPAP005 Coupled Bunch Instability Caused by Electron Cloud 943
 
  • M. Tobiyama, J.W. Flanagan, H. Fukuma, S.-I. Kurokawa, K. Ohmi, S.S. Win
    KEK, Ibaraki
 
  Coupled bunch instability caused by electron cloud has been observed in some positron storage ring. We discuss the mode spectrum of the coupled bunch instability due to electrons moving in drift space, weak solenoid field and strong bending field. The mode spectrum of the instability is reflected by the electron motion: that is, we understand global characteristics of elecron motion from the mode spectrum.  
FPAP007 Measurement of the Electron Cloud Density Around the Beam 1054
 
  • K.-I. Kanazawa, H. Fukuma, H. Hisamatsu, Y. Suetsugu
    KEK, Ibaraki
 
  Under the present operating condition of KEKB LER, most high energy electrons in the electron cloud that hit the chamber wall are produced near the circulating bunch by the single kick. By separating the high energy component of the electron current monitored at a pump port of a vacuum chamber, the density of the electron cloud near the beam is estimated. The estimated density is close to the order of magnitude expected from simulation. At present there still remains an ambiguity that comes from the detector efficiency in the measurement and the assumed secondary electron yield in the simulation.  
FPAP011 New Vortices in Axisymmetric Beams in Inhomogeneous Magnetic Field
 
  • Y. Golub
    MRTI RAS, Moscow
 
  We analyzed localized vortices in non-neutral inhomogeneous by density and velocity electron beams propagating in vacuum along the inhomogeneous external magnetic field. These vortices distinguish from vortices, which used in Golub Yu.Ya. et al. and Golub Yu.Ya. because of inhomogeneous external magnetic field. Also new types of vortex are obtained by new solution method of nonlinear equations.** The new method is development of a method described in Golub Yu.Ya. That method distinguish from standard Larichev-Reznik or Reznik method, which used in Golub Yu.Ya. et al. It has been found new expression for electric field potential of vortex in a wave frame. The expression is axisymmetric in a wave frame. New vortices are new solitons in the inhomogeneous external magnetic field.

*Golub Yu.Ya. et al., in Nonlinear world: IV Intern. Workshop on Nonlin. and Turbul. Proc. in Phys., (ed. by V.G. Bar'yakhtar et al.) World Scientific Publishing Co. Pte. Ltd., Singapore, 1990, vol. 2, p. 857. **Golub Yu.Ya., Proceedings of EPAC 2002, Paris, France, p. 1253.

 
FPAP012 The Effect of Inhomogeneous Magnetic Field on Budker-Chirikov Instability
 
  • Y. Golub
    MRTI RAS, Moscow
 
  The two-beams electron - ion system consists of a nonrelativistic ion beam propagating co-axially with a high-current relativistic electron beam in a longitudinal inhomogeneous magnetic field. The effect of the longitudinal inhomogeneous magnetic field on instability Budker-Chirikov (BCI) in the system is investigated by the method of a numerical simulation in terms of the kinetic description of both beams. The investigations are development of investigations in*,**. Is shown, when the inhomogeneity magnetic field results in the decreasing of an increment of instability Budker-Chirikov and the increasing of length of propagation of a electron beam. Also is shown, when take place the opposite result.

*Yu.Ya. Golub, N.E.Rozanov, Nuclear Instruments and Methods in Physics Research, A358 (1995) 479. **Yu.Ya. Golub, Proceedings of EPAC 2002, Paris, France, p. 1497.

 
FPAP013 Emittance Growth Caused by Electron Cloud Below the “Fast TMCI” Threshold: Numerical Noise or True Physics? 1344
 
  • E. Benedetto, E. Benedetto
    Politecnico di Torino, Torino
  • G. Franchetti
    GSI, Darmstadt
  • K. Ohmi
    KEK, Ibaraki
  • D. Schulte, F. Zimmermann
    CERN, Geneva
 
  Simulations show a persisting slow emittance growth for electron cloud densities below the threshold of the fast Transverse Mode Coupling type instability, which could prove important for proton beams with negligible radiation damping, such as in the LHC. We report on a variety of studies performed to quantify the contributions to the simulated emittance growth from numerical noise in the PIC module and from an artificial resonance excitation due to the finite number of kicks per turn applied for modeling the cloud-bunch interaction.  
FPAP014 Electron Cloud Measurements in the SPS in 2004 1371
 
  • D. Schulte, G. Arduini, V. Baglin, J.M. Jimenez, F. Zimmermann
    CERN, Geneva
 
  Novel measurements of the electron cloud have been performed in the SPS in 2004. In this machine the beam consists of a number of short bunch trains. By varying the distance between these trains it is possible to witness the survival of the electrons after the bunch passage. In this paper, results from simulations and experiments are compared.  
FPAP015 Electron and Gas Effects on Intense, Space-Charge Dominated Ion Beams in Magnetic Quadrupoles: Comparison of Experiments and Simulations
 
  • P.A. Seidl, D. Baca, F.M. Bieniosek, J.-L. Vay
    LBNL, Berkeley, California
  • R.H. Cohen, A. Friedman, D.P. Grote, M. Kireeff Covo, S.M. Lund, A.W. Molvik
    LLNL, Livermore, California
 
  Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL and LBNL under contracts W-7405-Eng-48, and DE-AC03-76F00098.

Accelerators for inertial fusion energy, high-energy density physics and other high intensity applications have an economic incentive to minimize the clearance between the beam edge and the aperture wall. This increases the risk from electron clouds and gas desorbed from walls. Using the High Current Experiment at LBNL, we have measured the beam (0.18 A, 1 MeV K+ ) distribution upstream and downstream of a short lattice of magnetic quadrupoles where the 2·rms beam size is =50% of the quadrupole aperture, and the generalized perveance is 10-3. Between magnets, the transverse beam distribution is also imaged. The beam potential is 1-2 kV, large enough to trap electrons produced by, for example, K+ - gas collisions. Gas and electron effects are intentionally induced by varying gas pressure and the bias of e- controlling electrodes.* The measurements are compared to WARP PIC simulations that include the self-consistent tracking of electrons and ions.**

*A. W. Molvik et al., this conference. **J-L Vay et al., this conference.

 
FPAP016 Initial Self-Consistent 3-D Electron-Cloud Simulations of LHC Beam with the Code WARP+POSINST 1479
 
  • J.-L. Vay, M.A. Furman
    LBNL, Berkeley, California
  • R.H. Cohen, A. Friedman, D.P. Grote
    LLNL, Livermore, California
 
  Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL and LBNL under contracts W-7405-Eng-48, and DE-AC03-76F00098.

We present initial results from the self-consistent beam-cloud dynamics simulations of a sample LHC beam, using a newly developed set of modeling capability based on a merger of the three-dimensional parallel Particle-In-Cell accelerator code WARP and the electron cloud code POSINST.*,** Although the storage ring model we use as a test bed to contain the beam is much simpler and shorter than the LHC, its lattice elements are realistically modeled, as is the beam and the electron cloud dynamics. The simulated mechanisms for generation and absorption of the electrons at the walls are based on previously validated models available in POSINST.***

*J.-L. Vay, these proceedings. **J.-L. Vay, Proc. "ECLOUD04," Napa (California), 2004. ***M.T.F. Pivi and M.A. Furman, Phys. Rev. STAB, PRSTAB/v6/i3/e034201.

 
FPAP017 Luminosity Optimization With Offset, Crossing Angle, and Distortion 1541
 
  • J. Wu, T.O. Raubenheimer
    SLAC, Menlo Park, California
 
  Funding: Work is supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.

In a linear collider, sources of beam jitter due to kicker noise, quadrupole vibration and long-range transverse wakefields will lead to beam offsets and tilts at the Intersection Point (IP). In addition, sources of emittance dilution such as short-range transverse wakefields or dispersive errors will lead to internal beam distortions. When the IP disruption parameter is large, these beam imperfections will be amplified by a single bunch kink instability which will lead to luminosity loss. In this paper, we study the luminosity loss and then the optimization required to cancel the luminosity loss first analytically and then with simulation.

 
FPAP018 Luminosity Loss Due to Beam Distortion and the Beam-Beam Instability 1586
 
  • J. Wu, A. Chao, T.O. Raubenheimer, A. Seryi
    SLAC, Menlo Park, California
  • C.K. Sramek
    Rice University, Houston, Texas
 
  Funding: Work is supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.

In a linear collider, sources of emittance dilution such as transverse wakefields or dispersive errors will couple the vertical phase space to the longitudinal position within the beam (the so-called ‘banana effect'). When the Intersection Point (IP) disruption parameter is large, these beam distortions will be amplified by a single bunch kink instability which will lead to luminosity loss. We study this phenomena both analytically using linear theory and via numerical simulation. In particular, we examine the dependence of the luminosity loss on the wavelength of the beam distortions and the disruption parameter. This analysis may prove useful when optimizing the vertical disruption parameter for luminosity operation with given beam distortions.

 
FPAP020 Close-Coupling R-Matrix Approach to Simulating Ion-Atom Collisions for Accelerator Applications 1685
 
  • P. Stoltz, A. Prideaux
    Tech-X, Boulder, Colorado
 
  Funding: Funded by DOE under grant # DE-FG02-02ER83553.

We have implemented an R-matrix close coupling approach to calculate capture, ionization, stripping and excitation cross-sections for 0.5 to 8.0 MeV K+ incident on Ar. This is relevant to the High Current Experiment at Lawrence Berkley National Laboratory. These cross sections are used to model accelerator particle dynamics where background gasses can interfere with beam quality. This code is a semi-classical approach that uses quantum mechanics to describe the particle interactions and uses classical mechanics to describe the nuclei trajectories. We compare a hydrogenic approximation for K+ with a pseudo-potential approach. Further we are developing a variational approach to quickly determine the best pseudo-potential parameters. Since many R-Matrix computationalists use this pseudo-potential approach, this approach will be useful for helping generate cross sections for any collision system.

 
FPAP021 A Cross-Platform Numerical Model of Ion-Wall Collisions 1707
 
  • S.A. Veitzer, P. Stoltz
    Tech-X, Boulder, Colorado
  • R.H. Cohen, A.W. Molvik
    LLNL, Livermore, California
  • J.-L. Vay
    LBNL, Berkeley, California
 
  Ion collisions with beam-pipe walls is a significant source of secondary electron clouds and desorbed neutral gasses in particle accelerators. Ions may reflect from beam-pipe walls and undergo further collisions downstream. These effects can cause beam degradation and are expected to be problematic in the design of heavy ion accelerators. The well-known SRIM code provides physically-based monte carlo simulations of ion-wall collisions. However, it is difficult to interface SRIM with high-performance simulation codes. We present details on the development of a package of Python modules which integrate the simulation of ion-wall interactions at grazing incidences with the high-performance particle-in-cell and electron cloud codes WARP and POSINST. This software package, called GriPY, calculates reflected angles and energies of ions which strike beam-pipe walls at grazing incidences, based upon interpolation of monte carlo statistics generated by benchmark simulations run in SRIM for a variety of relevant incident angles and energies. We present here solutions for 1.8 MeV K+ ions and 1 Gev protons incident on stainless steel.  
FPAP022 Long Time Simulation of LHC Beam Propagation in Electron Clouds 1769
 
  • B. Feng, A.F. Ghalam, T.C. Katsouleas
    USC, Los Angeles, California
  • E. Benedetto, F. Zimmermann
    CERN, Geneva
  • V.K. Decyk, W.B. Mori
    UCLA, Los Angeles, California
 
  In this report we show the simulation results of single-bunch instabilities caused by interaction of a proton beam with an electron cloud for the Large Hadron Collider (LHC) using the code QuickPIC [1]. We describe three new results: 1) We test the effect of the space charge of the beam on itself; 2) we add the effect of dispersion in the equation of motion in the x direction, and 3) we extend previous modeling by an order of magnitude (from 50ms to 500ms) of beam circulation time. The effect of including space charge is to change the emittance growth by less than a few percent. Including dispersion changes the plane of instability but keeps the total emittance approximately the same. The longer runs indicate that the long term growth of electron cloud instability of the LHC beam cannot be obtained by extrapolating the results of short runs.  
FPAP024 Electron Cloud in the Collimator- and Injection- Region of the Spallation Neutron Source's Accumulator Ring 1865
 
  • L. Wang, H.-C. Hseuh, Y.Y. Lee, D. Raparia, J. Wei
    BNL, Upton, Long Island, New York
  • S.M. Cousineau, S. Henderson
    ORNL, Oak Ridge, Tennessee
 
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge.

The beam loss along the Spallation Neutron Source’s (SNS’s) accumulator ring is mainly located at the collimator region. From the ORBIT simulation, the peak power deposition at the three collimators is about 500, 350 and 240 W/m, respectively. Therefore, a sizeable number of electrons may be accumulated at this region due to the great beam loss. This paper simulated the electron cloud at the collimator region and the possible remedy.

 
FPAP026 Multispecies Weibel Instability for Intense Ion Beam Propagation Through Background Plasma 1952
 
  • R.C. Davidson, S.R. Hudson, I. Kaganovich, H. Qin, E. Startsev
    PPPL, Princeton, New Jersey
 
  Funding: Research supported by the U.S. Department of Energy.

In application of heavy ion beams to high energy density physics and fusion, background plasma is utilized to neutralize the beam space charge during drift compression and/or final focus of the ion beam. It is important to minimize the deleterious effects of collective instabilities on beam quality associated with beam-plasma interactions. Plasma electrons tend to neutralize both the space charge and current of the beam ions. It is shown that the presence of the return current greatly modifies the electromagnetic Weibel instability (also called the filamentation instability), i.e., the growth rate of the filamentation instability greatly increases if the background ions are much lighter than the beam ions and the plasma density is comparable to the ion beam density. This may preclude using underdense plasma of light gases in heavy ion beam applications. It is also shown that the return current may be subject to the fast electrostatic two-stream instability.

 
FPAP027 Hybrid Quantum Mechanical–Quasi-Classical Model for Evaluating Ionization and Stripping Cross Sections in Atom-Ion Collisions 1988
 
  • I. Kaganovich, R.C. Davidson, E. Startsev
    PPPL, Princeton, New Jersey
 
  Funding: Research supported by the U.S. Department of Energy.

Ion-atom ionization cross sections are needed in many applications employing the propagation of fast ions through matter. When experimental data or full-scale theoretical calculations are non-existent, approximate methods must be used. The most robust and easy-to-use approximations include the Born approximation of quantum mechanics and the quasi-classical approach utilizing classical mechanics together with the Bohr-Sommerfeld quantization rule.* The simplest method to extend the validity of both approaches is to combine them, i.e., use the two different approaches but only for the regions of impact parameters in which they are valid, and sum the results to obtain the total cross section. We have recently investigated theoretically and experimentally the stripping of more than 18 different pairs of projectile and target atoms in the range of 3-38 MeV/amu to study the range of validity of various approximations. The results of the modified approach agree better with the experimental data than either the Born approximation or the quasi-classical approach, applied separately.

*I. D. Kaganovich et al., "Formulary and scaling cross sections for ion-atom impact ionization," http://arxiv.org/abs/physics/0407140.

 
FPAP028 Ion Beam Pulse Interaction with Background Plasma in a Solenoidal Magnetic Field 2062
 
  • I. Kaganovich, R.C. Davidson, E. Startsev
    PPPL, Princeton, New Jersey
 
  Funding: Research supported by the U.S. Department of Energy.

Background plasma can be used as an effective neutralization scheme to transport and compress intense ion beam pulses, and the application of a solenoidal magnetic field allows additional control and focusing of the beam pulse. Ion beam pulse propagation in a background plasma immersed in an applied solenoidal magnetic field has been studied both analytically and numerically with three different particle-in-cell codes (LSP, OOPIC-Pro and EDPIC) to cross-check the validity of the results. Very good charge and current neutralization is observed for high values of the solenoidal magnetic field.* However, for intermediate values of the solenoidal magnetic field, current neutralization is a complex process, and a sizable self-magnetic field is generated at the head of the beam. Collective wave excitations are also generated ahead of the beam pulse.

*I. D. Kaganovich, E. A. Startsev and R. C. Davidson, Nuclear Instruments and Methods in Physics Research A, in press (2004).

 
FPAP029 Nonlinear Delta-f Particle Simulations of Collective Effects in High-Intensity Bunched Beams 2107
 
  • H. Qin, R.C. Davidson, S.R. Hudson, E. Startsev
    PPPL, Princeton, New Jersey
 
  Funding: Research supported by the U.S. Department of Energy.

The collective effects in high-intensity 3D bunched beams are described self-consistently by the nonlinear Vlasov-Maxwell equations.* The nonlinear delta-f method,** a particle simulation method for solving the nonlinear Vlasov-Maxwell equations, is being used to study the collective effects in high-intensity 3D bunched beams. The delta-f method, as a nonlinear perturbative scheme, splits the distribution function into equilibrium and perturbed parts. The perturbed distribution function is represented as a weighted summation over discrete particles, where the particle orbits are advanced by equations of motion in the focusing field and self-consistent fields, and the particle weights are advanced by the coupling between the perturbed fields and the zero-order distribution function. The nonlinear delta-f method exhibits minimal noise and accuracy problems in comparison with standard particle-in-cell simulations. A self-consistent 3D kinetic equilibrium is first established for high intensity bunched beams. Then, the collective excitations of the equilibrium are systematically investigated using the nonlinear delta-f method implemented in the Beam Equilibrium Stability and Transport (BEST) code.

*R.C. Davidson and H. Qin, Physics of Intense Charged Particle Beams in High Energy Accelerators (World Scientific, 2001). **H. Qin, Physics of Plasmas 10, 2078 (2003).

 
FPAP031 Model of Electron Cloud Build Up with Secondary Ion-Electron Emission as a Source of Delayed Electrons 2197
 
  • V.G. Dudnikov, G. Dudnikova
    BTG, New York
 
  For explanation of anomaly long electron cloud surviving after the gap between bunches it was proposed beam particle leaking to the gap and anomaly high reflectivity of low energy electrons in collision with pipe wall. We will attract an attention to some other possibilities of efficient electron generation in the high vacuum environment and delay electron generation after gap between bunches. Model of electron cloud build up with secondary ion-electron emission as a source of delay electrons is presented and discussed. This model is used for explanation of bunched beam instability in Los Alamos PSR, prediction of e-cloud generation in SNS, and can be important for pressure rise in cold sections of RHIC. A fast desorbtion by ion of physically adsorbed molecules can explain a "first pulse Instability" observed in LA PSR  
FPAP033 Beam Energy Scaling of Ion-Induced Electron Yield from K+ Ions Impact on Stainless Steel Surfaces 2287
 
  • M. Kireeff Covo, J.J. Barnard, R.H. Cohen, A. Friedman, D.P. Grote, S.M. Lund, A.W. Molvik, G.A. Westenskow
    LLNL, Livermore, California
  • D. Baca, F.M. Bieniosek, C.M. Celata, J.W. Kwan, P.A. Seidl, J.-L. Vay
    LBNL, Berkeley, California
  • J.L. Vujic
    UCB, Berkeley, California
 
  Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL under contract No. W-7405-Eng-48, and by LBNL under Contract DE-AC03-76F00098.

The cost of accelerators for heavy-ion inertial fusion energy (HIF) can be reduced by using the smallest possible clearance between the beam and the wall from the beamline. This increases beam loss to the walls, generating ion-induced electrons that could be trapped by beam space charge potential into an "electron cloud," which can cause degradation or loss of the ion beam. In order to understand the physical mechanism of production of ion-induced electrons we have measured impact of K+ ions with energies up to 400 KeV on stainless steel surfaces near grazing incidence, using the ion source test stand (STS-500) at LLNL. The electron yield will be discussed and compared with experimental measurements from 1 MeV K+ ions in the High-Current Experiment at LBNL.*

*A.W. Molvik et al., PRST-AB 7, 093202 (2004).

 
FPAP034 Space-Charge Transport Limits in Periodic Channels 2348
 
  • S.M. Lund
    LLNL, Livermore, California
  • S. R. Chawla
    UCB, Berkeley, California
 
  Funding: Research performed under the auspices of the US DOE by the University of California at LLNL and LBNL under contract Nos. W-7405-Eng-48 and DE-AC03-76SF00098.

It has been observed in both experiment and particle in cell simulations that space-charge-dominated beams suffer strong emittance growth in alternating gradient quadrupole transport channels when the undepressed phase advance σ0 increases beyond about 80 degrees per lattice period. Transport systems have long been designed to respect this phase advance limit but no theory has been proposed to date to explain the the cause of the limit. Here we propose a mechanism to parametrically explain the transport limit as being due to classes of halo particle orbits moving close to the beam edge in phase-space when σ0 increases beyond 80 degrees. A finite beam edge and/or perturbation acting on an edge particle can then act to move edge particles to large amplitude and lead to large increases in beam phase space area, lost particles, and degraded transport. A core particle model for a uniform density elliptical beam in a periodic focusing lattice was written and is applied to parametrically analyze this process for both periodic alternating gradient quadrupole and solenoidal transport lattices. Self-consistent particle in cell simulations are also carried out to support results.

 
FPAP036 Beam Transport in a Compact Dielectric Wall Induction Accelerator System for Pulsed Radiography 2437
 
  • J.F. McCarrick, G.J. Caporaso, Y.-J. Chen
    LLNL, Livermore, California
 
  Funding: This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

Using dielectric wall accelerator technology, we are developing a compact induction accelerator system primarily intended for pulsed radiography. The accelerator would provide a 2-kA beam with an energy of 8 MeV, for a 20-30 ns flat-top. The design goal is to generate a 2-mm diameter, 10-rad x-ray source. We have a physics design of the system from the injector to the x-ray converter. We will present the results of injector modeling and PIC simulations of beam transport. We will also discuss the predicted time integrated spot and the on-axis x-ray dose.