• C. P. Neuman
  
• P. G. O'Shea
  UMD, College Park, Maryland

(*) Simulation of Longitudinally Modulated Electron Beams. C. P. Neuman and P. G. O'Shea. In 2006 Advanced Accelerator Concepts Workshop, AIP Conference Proceedings, 877, 621-627. Melville, AIP (2006).

• C. P. Neuman
  
• P. G. O'Shea
  UMD, College Park, Maryland

(*) Simulation of Longitudinally Modulated Electron Beams. C. P. Neuman and P. G. O'Shea. In 2006 Advanced Accelerator Concepts Workshop, AIP Conference Proceedings 877, edited by M. Conde and C. Eyberger, 621-627. Melville, NY, AIP (2006).

• O. A. Anderson
  
• L. L. LoDestro
  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.

• J. E. Coleman
  
• E. P. Gilson, A. B. Sefkow
  PPPL, Princeton, New Jersey
• D. Ogata
  UCB, Berkeley, California
• P. K. Roy, P. A. Seidl
  LBNL, Berkeley, California
• D. R. Welch
  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.

• P. K. Roy
  
• J. J. Barnard, A. W. Molvik
  LLNL, Livermore, California
• F. M. Bieniosek, J. E. Coleman, J.-Y. Jung, M. Leitner, B. G. Logan, P. A. Seidl, W. L. Waldron
  LBNL, Berkeley, California
• R. C. Davidson, P. Efthimion, E. P. Gilson, A. B. Sefkow
  PPPL, Princeton, New Jersey
• J. A. Duersch, D. Ogata
  UCB, Berkeley, California
• D. R. Welch
  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.

• R. D. Ryne
  
• I. V. Pogorelov, J. Qiang
  LBNL, Berkeley, California

• K. G. Sonnad
  
• J. R. Cary
  CIPS, Boulder, Colorado
• M. A. Furman
  LBNL, Berkeley, California
• P. Stoltz, S. A. Veitzer
  Tech-X, Boulder, Colorado

Simulation studies are under way to analyze the dynamics of microwave transmission through a beam channel containing electron clouds. Such an interaction is expected to produce a shift in phase accompanied by attenuation in the amplitude of the microwave radiation. Experimental observation of these phenomena would lead to a useful diagnosis tool for electron clouds. This technique has already been studied* at the CERN SPS. Similar experiments are being proposed at the PEP-II LER at SLAC as well as the Fermilab MI. In this study, simulation results will be presented for a number of cases including those representative of the above mentioned experiments. The code VORPAL is being utilized to perform electromagnetic particle-in-cell (PIC) calculations. The results are expected to provide guidance to the above mentioned experiments as well as lead to a better understanding of the problem.

* T. Kroyer, F. Caspers, E. Mahner , pg 2212 Proc. PAC 2005, Knoxville, TN

• C. Xu
  
• C. K. Allen
  LANL, Los Alamos, New Mexico
• E. Schuster
  Lehigh University, Bethlehem, Pennsylvania

• M. Hess
  
• C. S. Park
  IUCF, Bloomington, Indiana

We present a multislice approach for modeling the space-charge fields of bunched electron beams that are emitted from a metallic cathode using electromagnetic Green's function techniques. The multislice approach approximates a local region of the beam density and current with a slice of zero longitudinal thickness. We show examples of how the multislice approach can be used to accurately compute the space-charge fields for electron bunch lengths in the regime of photocathode sources, i.e. (<10 ps).

• F. Lin
  
• L. Ahrens, M. Bai, K. A. Brown, E. D. Courant, J. Glenn, H. Huang, A. U. Luccio, W. W. MacKay, T. Roser, N. Tsoupas
  BNL, Upton, Long Island, New York
• S.-Y. Lee
  IUCF, Bloomington, Indiana

Two partial helical dipole snakes were found to be able to overcome all imperfection and intrinsic spin resonances provided that the vertical betatron tunes were maintained in the spin tune gap near the integer 9. Recent vertical betatron tune scan showed that the two weak resonances at the beginning of the acceleration cycle may be the cause of polarization loss. This result has been confirmed by the vertical polarization profile measurement, and spin tracking simulations. Possible cure of the remaining beam polarization is discussed.

• C. S. Park
  
• M. Hess
  IUCF, Bloomington, Indiana

We demonstrate the computational requirements for a Green's function based photocathode simulation code called IRPSS. In particular, we show the necessary conditions, e.g. eigenmode number and integration time-step, for accurately computing the space-charge fields in IRPSS to less than 1 % error. We also illustrate how numerical filtering methods can be applied to IRPSS in conjunction with a multislice approach, for dramatically improving computational efficiency of electromagnetic field calculations.

• Y. Sato
  
• J. A. Holmes
  ORNL, Oak Ridge, Tennessee
• S.-Y. Lee
  IUCF, Bloomington, Indiana
• R. J. Macek
  LANL, Los Alamos, New Mexico

We present ORBIT code simulations to examine the sensitivity of electron cloud properties to different proton beam profiles and to reproduce experimental results from the proton storage ring at Los Alamos National Laboratory. We study the recovery of electron clouds after sweeping, and also the characteristics of two types of electrons signals (prompt and swept) as functions of beam charge. The prompt signal means the peak height of electron sweeper signal before high voltage pulse applied on its electrode and after beam accumulation, and the swept signal means the spike height of electron sweeper signal during the high voltage pulse. To concentrate on the electron cloud dynamics, we use a cold proton bunch to generate primary electrons and electromagnetic field for electron dynamics. However, the protons receive no feedback from the electron cloud. Our simulations indicate that the proton loss rate in the field-free straight section might be an exponential function of proton beam charge and may also be lower than the averaged proton loss rate in a whole ring.

• T. L. Hart
  

• D. T. Abell
  
• P. J. Mullowney, K. Paul, V. H. Ranjbar
  Tech-X, Boulder, Colorado
• J. Qiang, R. D. Ryne
  LBNL, Berkeley, California

The standard implementation of using FFTs to solve the Poisson equation with open boundary conditions on a Cartesian grid loses accuracy when the change in G rho (the product of the Green function and the charge density) over a mesh cell becomes nonlinear; this is commonly encountered in high aspect ratio situations and results in poor efficiency due to the need for a very large number of grid points. A modification which solves this problem, the integrated Green function (IGF), has been implemented in two dimensions using linear basis functions and in three dimensions using constant basis functions. But, until recently, it has proved to be very difficult to implement IGF in three dimensions using linear basis functions. Recently significant progress has been made. We present both the implementation and test results for the three-dimensional extension.

• G. I. Bell
  
• I. Ben-Zvi, A. V. Fedotov, V. Litvinenko
  BNL, Upton, Long Island, New York
• D. L. Bruhwiler, A. V. Sobol
  Tech-X, Boulder, Colorado

The design of the high-energy cooler for the Relativistic Heavy Ion Collider (RHIC) recently adopted a non-magnetized approach. To prevent recombination between the fully stripped gold ions and co-propagating electrons, a helical undulator magnet has been proposed. In addition, to counteract space-charge defocusing, weak solenoids are proposed every 10m. To understand the effect of these magnets on the cooling rate, numerical models of cooling in the presence of external fields are needed. We present an approach from first principles using the VORPAL parallel simulation code. We solve the n-body problem by exact calculation of pair-wise collisions. Simulations of the proposed RHIC cooler are discussed, including fringe field and finite interaction time effects.

• D. R. Dechow
  
• D. T. Abell, P. Stoltz
  Tech-X, Boulder, Colorado
• J. F. Amundson
  Fermilab, Batavia, Illinois
• L. Curfman McInnes, B. Norris
  ANL, Argonne, Illinois

A component-based beam dynamics application for modeling collective effects in particle accelerators has been developed. The Common Component Architecture (CCA) software infrastructure was used to compose a new Python-steered accelerator simulation from a set of services provided by two separate beam dynamics packages (Synergia and MaryLie/Impact) and two high-performance computer science packages (PETSc and FFTW). The development of the proof-of-concept application was accomplished via the following tasks:

1. addressing multilanguage interoperability in the MaryLie/Impact code with Babel;
2. creating components by making the selected software objects adhere to the Common Component Architecture protocol;
3. assemblying the components with a newly developed, Component Builder gui; and
4. characterizing the performance of the space charge (Poisson) solver that was originally used in Synergia 1.0 versus the PETSc-based space charge solver that has been developed for Synergia2.

• D. A. Dimitrov
  
• I. Ben-Zvi, X. Chang, T. Rao, J. Smedley, Q. Wu
  BNL, Upton, Long Island, New York
• D. L. Bruhwiler, R. Busby, J. R. Cary
  Tech-X, Boulder, Colorado

The work at Tech-X Corp. is supported by the U. S. Department of Energy under a Phase I SBIR grant.

• K. R. Samokhvalova
  
• C. Chen, J. Z. Zhou
  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.

• S. Bernal
  
• B. L. Beaudoin, R. A. Kishek, P. G. O'Shea, M. Reiser, D. F. Sutter
  UMD, College Park, Maryland

The University of Maryland Electron Ring (UMER) is designed for the transport of low energy (10 keV), high current (100 mA) electrons in a 72-magnetic-quadrupole lattice over an 11.5 m circumference. With these parameters, and a typical single-particle phase advance per period of 76 deg., space charge is extreme. However, high current is not necessary for establishing space charge dominated transport in UMER. In fact, low current (0.6 mA) beam transport in combination with longer full-lattice periods can yield strong space charge conditions. All 72 quadrupoles are needed, though, to yield beams with relatively small cross sections, as required for emittance-dominated transport. We present results of calculations and experiments that demonstrate the low-current, high space charge regime in UMER. We also discuss the use of Collins-type insertions for matching into the ring lattice.

• I. Haber
  
• S. Bernal, R. Feldman, R. A. Kishek, P. G. O'Shea, C. Papadopoulos, M. Reiser, D. Stratakis, M. Walter
  UMD, College Park, Maryland
• A. Friedman, D. P. Grote
  LLNL, Livermore, California
• J.-L. Vay
  LBNL, Berkeley, California

One of the areas fundamental beam physics that serve as the rationale for recent research on UMER is the study of generation and evolution of beam halos. This physics can be accessed on a scaled basis in UMER at a small fraction of the cost of similar experiments on a much larger machine. Recent experiments and simulations have identified imperfections in the source geometry, particularly in the region near the emitter edge, as a potentially significant source of halo particles. The edge-generated halo particles, both in the experiments and the simulations are found to pass through the center of the beam in the vicinity of the anode plane. Understanding the detailed evolution of these particle orbits is therefore important to designing any aperture to remove the beam halo. Both experimental data and simulations will be presented to illustrate the details of this mechanism for halo formation.

• C. Papadopoulos
  
• G. Bai, B. L. Beaudoin, I. Haber, R. A. Kishek, P. G. O'Shea, M. Reiser, M. Walter
  UMD, College Park, Maryland

This is a numerical study of the effects of skew quadrupoles on the beam used in University of Maryland Electron Ring (UMER). As this beam is space-charge dominated, we expect new phenomena to be present compared to the emittance-dominated case. In our studies we find that skew quadrupoles can severely affect the halo of the beam and cause emittance growth, even in the first turn of the beam. For our simulations we used the WARP particle-in-cell code and we compared the results with the experimental study of skew quadrupole effects (to be reported separately).

• J. C.T. Thangaraj
  
• G. Bai, B. L. Beaudoin, S. Bernal, D. W. Feldman, R. B. Fiorito, I. Haber, R. A. Kishek, P. G. O'Shea, M. Reiser, D. Stratakis, D. F. Sutter, K. Tian, M. Walter
  UMD, College Park, Maryland

The University of Maryland Electron Ring (UMER) is a scaled model to investigate the transverse and longitudinal physics of space charge dominated beams. It uses a 10-keV electron beam along with other scaled beam parameters that model the larger machines but at a lower cost. Understanding collective behavior of intense, charged particle beams due to their space charge effects is crucial for advanced accelerator research and applications. This paper presents the experimental study of longitudinal dynamics of an initial density modulation on a spacecharge dominated beam. A novel experimental technique of producing a perturbation using a laser is discussed. Using a laser to produce a perturbation provides the ability to launch a pure density modulation and to have better control over the amount of perturbation introduced. Collective effects like space charge waves and its propagation over long distances in a quadrupole channel are studied. One dimensional cold fluid model is used for theoretical analysis and simulations are carried out in WARP-RZ.

• K. Tian
  
• G. Bai, B. L. Beaudoin, D. W. Feldman, R. B. Fiorito, I. Haber, R. A. Kishek, P. G. O'Shea, M. Reiser, D. Stratakis, D. F. Sutter, J. C.T. Thangaraj, M. Walter, C. Wu
  UMD, College Park, Maryland

Longitudinal perturbations can be generated in the space-charge dominated regimes in which most beams of interest are born. To study the modification of transverse beam distributions by longitudinal beam dynamics, we have conducted experimental studies using low energy electron beams by taking time resolved images of a beam with longitudinal density perturbations. Two different diagnostics are used: optical transition radiation (OTR) produced from an intercepting silicon based aluminum screen and a fast (<5ns decay time) phosphor screen. It is found that the beam is significantly affected by the perturbation. However the OTR signal is very weak and requires over 45 minutes of frame integration. The fast phosphor screen has much better sensitivity (~1'000 times enhancement). In this paper, we also report on the time resolved measurement of a parabolic beam, showing interesting correlations between transverse and longitudinal distributions of the beam.

• B. Erdelyi
  
• L. L. Bandura
  Northern Illinois University, DeKalb, Illinois
• S. L. Manikonda, J. A. Nolen
  ANL, Argonne, Illinois

An Exotic Beam Facility is one of the highest priority projects in the DOE 20-year plan and a major strategic initiative for Argonne. The main components of the facility are a high-power multi-beam superconducting heavy-ion accelerator, a production complex, and finally a high-efficiency post-accelerator. This talk revolves around new approaches to heavy-ion beam dynamics for the central part, the Fragment Separators. To this end, it will summmarize the theories developed, software written, and simulations done that lead to better understanding of basic beam dynamics, more insight towards the best design choices, and optimization of the system?s parameters, including the integrated beam optics-nuclear physics approach.

• G. H. Gillespie
  
• W. Hill
  G. H. Gillespie Associates, Inc., Del Mar, California

The Particle Beam Optics Laboratory, or PBO Lab, is a suite of software applications developed to support beamline design, accelerator operations, and personnel training. The software provides an intuitive and easy-to-use graphic user interface (GUI) that works with a variety of particle optics codes. The PBO Lab GUI is largely responsible for the popularity of this software suite, which is now used at more than ninety institutions throughout the world. While PBO Lab greatly improves the human-machine interface for several popular optics programs, it has historically required a significant effort to incorporate additional optics codes into the software suite. The Open Architecture Software Integration System, or OASIS, provides an innovative framework that allows users to readily integrate their own optics programs into PBO Lab. This paper provides an overview of the OASIS framework and describes some of the new PBO Lab Modules that have been created using OASIS.

• J. Li
  
• S. Huang, S. F. Mikhailov, V. Popov, Y. K. Wu
  FEL/Duke University, Durham, North Carolina

As part of the High Intensity Gamma-Ray Source (HIGS) upgrade, the booster synchrotron has been recently commissioned. The booster ramps the electron beam between 0.27 and 1.2 GeV for top-off injection into the Duke storage ring. It has symmetrical injection/extraction schemes with a bumped orbit. The injection/extraction kickers and corresponding septa are located in the opposite straight sections of the booster ring separated by about 1/4 of the vertical betatron wave. Due to the nonideal properties of the magnetic material, the magnetic field leaks out into the stored beam chamber, which directly results in orbit distortion, tune and chromaticity shifts and change of coupling. These effects caused by the extraction septum have been measured as a function of extraction energy. Based upon the measurements, we have developed a scheme to compensate the dynamics effects mentioned above.

• M. Doleans
  
• V. Andreev, B. Arend, D. Bazin, A. Becerril Reyes, R. Fontus, P. Glennon, D. Gorelov, P. F. Mantica, J. Ottarson, H. Schatz, B. Sherrill, J. Stoker, O. Tarasov, J. Vincent, J. Wagner, X. Wu, A. Zeller
  NSCL, East Lansing, Michigan

* D. Gorelov, V. Andreev, D. Bazin, M. Doleans, T. Grimm, F. Marti, J. Vincent and X. Wu, "RF-Kicker System for Secondary Beams at NSCL/MSU" PAC2005, Knoxville, Tennessee, 16th-20th, May 2005

• G. K. Pang
  
• G. Bollen, S. Chouhan, C. Guenaut, D. Lawton, F. Marti, D. J. Morrissey, J. Ottarson, S. Schwarz, A. Zeller
  NSCL, East Lansing, Michigan
• M. Wada
  RIKEN, Saitama

Gas stopping is the method of choice to convert high-energy beams of rare isotopes produced by projectile fragmentation into low-energy beams. Fast ions are slowed down in solid degraders and stopped in a buffer gas in a stopping cell, presently linear. They have been successfully used for first precision experiments with rare isotopes*,** but they have beam-rate limitations due to space charge effects. Their extraction time is about 100 ms inducing decay losses for short-lived isotopes. At the NSCL a new gas stopper concept*** is under development, which avoids these limitations and fulfills the needs of next-generation rare isotope beam facilities. It uses a gas-filled cyclotron magnet. The large volume, and a separation of the regions where the ions stop and where the maximum ionization is observed are the key to a higher beam-rate capability. The longer stopping path due to the magnetic field allows a lower pressure to be used, which decreases the extraction times. The concepts of the cyclotron gas stopper will be discussed and the results from detailed simulation and design work towards the realization of such a device at the NSCL will be summarized.

* G. Bollen et al., Phys. Rev. Lett. 96 (2006) 152501 ** R. Ringle Phys. Rev. C Submitted*** G. Bollen et al., Nucl. Instr. Meth. A550 (2005) 27

• B. W. Buckley
  
• G. Hoffstaetter
  CLASSE, Ithaca

One of the main concerns in the design of a high energy Energy Recovery Linac x-ray source is the preservation of beam emittance. Discussed is one possible source of emittance dilution due to transverse electromagnetic fields in the accelerating cavities of the linac caused by the power coupler geometry. This has already been found to be a significant effect in Cornell's ERL injector cavities if only one coupler per cavity is chosen. Here we present results of simulations for Cornell's main ERL linac with three possible coupler configurations and compare them with regards to total normalized emittance growth after one complete pass through the linac. We explain why the sign of the phase between the transverse kick and the accelerating force alternates each cavity, which leads to a cancellation of the emittance growth to acceptable values. We also investigate the effect of cavity detuning on the coupler-kick effect.

• J. Shi
  
• G. Hoffstaetter
  CLASSE, Ithaca

A self-consistant simulation method is developed for the study of coherent synchrotron radiation effects by using a perturbation expansion of retarded radiation field and the particle-in-cell method. The perturbation expansion of the radiation field is based on the fact that the time dependance of a bunch particle distribution has typically two significantly different time scales, a fast time scale related to the linear dynamics and a slow time scale of the beam-size growth due to nonlinear perturbations. Since the scale of the retardation of the radiation field is usually much shorter than the slow time scale of the particle distribution, the retardation on the slow time scale of the particle distribution is treated perturbatively while the retardation on the fast time scale is removed by transformations associated the linear lattice. With this method, the particle-radiation interaction can be calculated in configuration space without memorizing the history of the particle distribution.

• J. R. Harris
  
• R. Feldman, P. G. O'Shea
  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.

• J. F. DeFord
  
• B. Held
  STAR, Inc., Mequon, Wisconsin
• J. J. Petillo
  SAIC, Burlington, Massachusetts

Particle orbit errors in multipacting and dark current computations can arise from inadequate field representation, poor surface modeling, and from the integration algorithm used to advance the particles. Established fields-based adaptive mesh refinement (AMR) methods *,** selectively improve the field and surface representation over several iterations in finite-element codes but they are not optimized for particle tracking. In particular, field emission and secondary emission models require precise surface representations and highly accurate field representations near surfaces, and these requirements are not adequately addressed in standard AMR techniques. In this paper we report on extensions to existing AMR support in the Analyst software package for particle tracking, including adaptive improvement of near-surface and on-surface field representations, and control of element aspect ratios throughout successive iterations. We also discuss the merits of automated identification of important regions of the mesh based on field levels and orbit estimation to guide AMR in multipacting calculations, and multipacting results for a SRF cavity will be presented.

* G. Drago, et al., IEEE Trans. on Mag., 28, 1992, pp. 1743-1746.** D. K. Sun, et al., IEEE Trans. on Mag., 36, July 2000, pp. 1596-1599.

• W. M. Sharp
  
• R. H. Cohen, A. Friedman, D. P. Grote, A. W. Molvik
  LLNL, Livermore, California
• J. E. Coleman, P. K. Roy, P. A. Seidl, J.-L. Vay
  LBNL, Berkeley, California
• I. Haber
  UMD, College Park, Maryland

Contamination from electrons is a concern for solenoid-focused ion accelerators being developed for experiments in high-energy-density physics (HEDP). These electrons, produced directly by beam ions hitting lattice elements or indirectly by ionization of desorbed neutral gas, can potentially alter the beam dynamics, leading to a time-varying focal spot, increased emittance, halo, and possibly electron-ion instabilities. The electrostatic particle-in-cell code WARP is used to simulate electron-cloud studies on the solenoid-transport experiment (STX) at Lawrence Berkeley National Laboratory. We present self-consistent simulations of several STX configurations to show the evolution of the electron and ion-beam distributions first in idealized 2-D solenoid fields and then in the 3-D field values obtained from probes. Comparisons are made with experimental data, and several techniques to mitigate electron effects are demonstrated numerically.

• T. P. Wangler
  
• V. N. Aseev, B. Mustapha, P. N. Ostroumov
  ANL, Argonne, Illinois
• J. H. Billen, R. W. Garnett
  LANL, Los Alamos, New Mexico
• K. R. Crandall
  TechSource, Santa Fe, New Mexico
• M. Doleans, D. Gorelov, X. Wu, R. C. York, Q. Zhao
  NSCL, East Lansing, Michigan
• J. Qiang, R. D. Ryne
  LBNL, Berkeley, California

RIAPMTQ/IMPACT is a pair of linked beam-dynamics simulation codes that have been developed for end-to-end computer simulations of multiple-charge state heavy-ion linacs for future exotic-beam facilities. The simulations can extend from the low-energy beam transport after the ECR source to the end of the linac. The work has been performed by a collaboration including LANL, LBNL, ANL, MSU, and TechSource. The code RIAPMTQ simulates the linac front end including the LEBT, RFQ, and MEBT, and the code IMPACT simulates the main superconducting linac. The codes have been benchmarked for rms beam properties against previously existing codes at ANL and MSU. The codes allow high-statistics runs on parallel supercomputing platforms, such as NERSC at LBNL, as well as runs on desktop PC computers for low-statistics design work. We will show results from 10-million-particle simulations of RIA designs by ANL and MSU, carried out at the NERSC facility. These simulation codes will allow evaluations of candidate designs with respect to beam-dynamics performance including beam losses.

• A. Fukasawa
  
• D. Alesini, M. Ferrario, B. Spataro
  INFN/LNF, Frascati (Roma)
• A. Boni, B. D. O'Shea, J. B. Rosenzweig
  UCLA, Los Angeles, California
• L. Ficcadenti, A. Mostacci, L. Palumbo
  Rome University La Sapienza, Roma

• D. Schiller
  
• S. Reiche, M. Ruelas
  UCLA, Los Angeles, California

• B. Feng
  
• V. K. Decyk, C. Huang, W. B. Mori
  UCLA, Los Angeles, California
• T. C. Katsouleas, P. Muggli
  USC, Los Angeles, California

We proposed a novel algorithm, which uses pipelining to reduce the simulation time for beam-electron cloud interaction. In the pipelining algorithm the processors are divided into subgroups, and during the simulation different groups will be on consecutive time steps. The pipelining algorithm is applied to the fully parallelized Particle-In-Cell (PIC) code QuickPIC to overcome the limit of the number of processors that can be used at each time step. With the new algorithm, the accuracy of the simulation is preserved; and the speed of the simulation is improved by a factor proportional to the number of processors available. The long term beam evolution results for the CERN-LHC and the FNAL main injector are presented using the QuickPIC with pipelining algorithm.

• F.-J. Decker
  
• Y. Nosochkov, M. K. Sullivan, G. Yocky
  SLAC, Menlo Park, California

Orbit bumps in sextupoles are routinely used for tuning the luminosity in the PEP-II B-Factory. Anti-symmetric bumps in a sextupole pair generate dispersion, while symmetric bumps induce a tune shift and beta beat. By coming two of these symmetric bumps with opposite signs where the second pair is 90 degree away, the tune shift cancels and the beta beat doubles. In the low energy ring (LER) we have four sextupole pairs per arc, where pair 1 and 3 are at the same betatron phase and pair 2 and 4are 90 degree away. By making two symmetric bumps with opposite sign in pair 1 and 3 the tune shift and the beta beat outside this region cancel, BUT the LER lifetime improved by a factor of three, losses by a factor of five, and the beam-beam background in the drift chamber of the BaBar detector by 20%. Simulations showed that the phase change at the second sextupole pair introduced by the beta beat can completely cancel the third order chromaticity.

• F.-J. Decker
  
• Y. Cai, Y. Nosochkov, Y. T. Yan, G. Yocky
  SLAC, Menlo Park, California

The low energy ring (LER) in PEP-II has a design emittance of 0.5 nm-rad in the vertical, compared to nearly 0.1 nm-rad for the HER ring. This was thought to come from the "vertical step" of about 1 m in the interaction straight, where the LER beam after horizontal separation gets bend vertical so it sits on top of the HER in the rest of the ring. Since the program MAD does not easily reveal the location of the major emittance contribution, a program was written to calculate the coupled "curly H" parameter of mode 2 (mainly vertical) along z. Weighting it with the magnet bending revealed that the weak long bends inside the "vertical step" did less than 20% of the emittance growth. More than 80% comes from the ends of the adjacent arcs with strong bends. This is caused by the coupling cancellation of the solenoid starting already there with the skew quadrupoles SK5 and 6. By introducing additional skews in the straight instead of SK5 and 6 the emittance could be reduced by a factor of ten in simulations, but with very strong skews. Reasonable strong magnets might generate a workable compromise, since a factor of two in emittance promises 50% more luminosity in beam-beam simulations.

• Y. T. Ding
  
• Z. Huang, C. Limborg-Deprey
  SLAC, Menlo Park, California
• J. Qiang
  LBNL, Berkeley, California

* J. Qiang et al, Phys. Rev. ST Accel. Beams 9,044204 (2006).

• A. C. Kabel
  
• W. Fischer
  BNL, Upton, Long Island, New York
• T. Sen
  Fermilab, Batavia, Illinois

• A. Krasnykh
  

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. Krasnykh
  

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.

• M. T.F. Pivi
  

We present the features of CMAD, a newly developed self-consistent code which simulates both the electron cloud build-up and related beam instabilities. By means of parallel (Message Passing Interface - MPI) computation, the code tracks the beam in an existing (MAD-type) lattice and continuously resolve the interaction between the beam and the cloud at each element location, with different cloud distributions at each magnet location. CMAD simulates single-and coupled-bunch instability, allows tune shift, dynamic aperture and frequency map analysis and the determination of the secondary electron yield instability threshold. Preliminary results are presented.

• L. Wang
  

Grooved surface is proposed to reduce the secondary emission yield in a dipole and wiggler magnet of International Linear Collider. An analysis of the impedance of the grooved surface based on adaptive finite element is presented in this paper. The performance of the adaptive algorithms, based on an element-element h-refinement technique, is assessed. The features of the refinement indictors, adaptation criteria and error estimation parameters are discussed.

• W. Wittmer
  

The PEP II lattices are unique in their detector solenoid field compensation scheme by utilizing a set of skew quadrupoles in the IR region and the adjacent arcs left and right from the IP. Additionally the design orbit through this region is nonzero. This combined with the strong local coupling wave makes it very difficult to calculate IP tuning knobs which are orthogonal and closed. The usual approach results either in non-closure, not being orthogonal or the change in magnet strength being too big. To find a solution the set of tuning quads had to be extended which resulted having more degrees of freedom than constrains. To find the optimal set of quadrupoles which creates a linear, orthogonal and closed knob and simultaneously minimizing the changes in magnet strength, the method using Singular Value Decomposition, Response Matrices and an Adapted Moore Penrose Method had to be extended. The results of these simulations are discussed below and the results of first implementation in the machine are shown.

• Y. T. Yan
  
• Y. Cai, W. S. Colocho, F.-J. Decker
  SLAC, Menlo Park, California

For optics measurement and modeling of the PEP-II electron (HER) and position (LER) storage rings, we have been doing well with MIA* which requires analyzing turn-by-turn Beam Position Monitor (BPM) data that are resonantly excited at the horizontal, vertical, and longitudinal tunes respectively. However, in anticipating that certain BPM buttons or even pins in the PEP-II IR region will be missing for the next run starting in January 2007, we have been developing a data validation process, hoping to reduce the effect due to the reduced BPM data accuracy on PEP-II optics measurement and modeling. Besides the routine process for ranking BPM noise level through data correlation among BPMs, allowing BPMs to have linear gains and linear cross couplings, we can also check BPM data symplecticity by comparing the invariant ratios. We may also work out nonlinear BPM data correction if needed. Results on PEP-II measurement will be presented.

* Y. T. Yan, et. al. EPAC06 Proceedings, WEPCH062, (2006)

• R. M. Bodenstein
  
• M. G. Tiefenback
  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.

• D. Douglas
  
• K. Beard, J. Eldred, P. Evtushenko, A. Jenkins, S. W. Moore, L. Osborne, D. W. Sexton, C. Tennant
  Jefferson Lab, Newport News, Virginia

Particle beam modeling in accelerators has been the focus of much effort (at great expense) since the 1950s. Several generations of tools have resulted from this process, each leveraging both the understanding provided by predecessors and the availability of increasingly powerful computer hardware. Nonetheless, the process remains on-going, in part due to innovations in accelerator design, construction, and operation that result in machines not easily described by existing tools. We discuss a novel response to this issue, which was encountered when Jefferson Lab began operation of its energy-recovering linacs. As such machines are not conveniently described using legacy software, a machine model was been built using Microsoft Excel. This interactive simulation can query data from the accelerator, use it to compute machine parameters, analyze difference orbit data, and evaluate beam properties. It can also derive new accelerator tunings and rapidly evaluate the impact of changes in machine configuration. As it is spreadsheet-based, it can be easily user-modified in response to changing requirements. Examples for the JLab IR Upgrade FEL are presented.

• R. Li
  

In this study, we analyze the longitudinal effective CSR force for an energy-chirped Gaussian bunch moving relativistically on a circular orbit. With the geometry of the bunch tilt in dispersive regions (as induced by the initial energy-chirp) included in the retardation relation, the longitudinal effective CSR force thus calculated displays a variety of behaviors depending on the level of bunch compression. The variety ranges from the suppression of the longitudinal CSR force, for an undercompressed thin bunch, to an enhancement of the CSR interaction above that for a projected bunch, in a duration of path length shortly after the bunch crosses over the full compression point. The amplitude and duration of the enhancement depends on the bunch and lattice parameters. During this enhancement, the longitudinal effective CSR force depends sensitively on the particle's transverse position in the bunch. The physical picture of this phenomenon will be discussed.

• J. A. Holmes
  
• M. R. Perkett
  Denison University, Granville, Ohio
• M. A. Plum, J.-G. Wang, Y. Zhang
  ORNL, Oak Ridge, Tennessee

Simulations of the transport of H⁰ and H^- beams to the SNS ring injection dump are carried out using the ORBIT code. During commissioning and early operations, beam losses in this region have been the highest in the accelerator and presented the most obvious hurdle to cross in achieving high intensity operation. Two tracking models are employed:

1. a piecewise continuous symplectic representation of the lattice elements in the injection chicane and dump line, and
2. particle tracking in full 3D magnetic fields, as obtained from OPERA code evaluations.

• J.-G. Wang
  

The SNS ring injection dump beam line has been suffering high beam losses since its commissioning. In order to understand the mechanisms of the beam losses, we have built a 3D simulation model consisting of three injection chicane dipoles and one injection dump septum. The magnetic field distributions and the 3D particle trajectories in the model are obtained. The study has clearly shown two design problems causing beam losses in the injection dump beam line. This paper reports our simulation model, particle trajectory calculations, beam losses due to small vertical aperture of the injection dump septum and inadequate focusing down stream. The remedy of the beam losses is also discussed.

• T. W. Koeth
  
• L. Bellantoni, D. A. Edwards, H. Edwards, R. P. Fliller
  Fermilab, Batavia, Illinois

An experiment is being constructed at Fermilab's A0 Photoinjector to exchange longitudinal and transverse beam emittances. The exchange is preformed by an optics channel consisting of two dogleg bend sections with a transverse deflecting mode cavity between them. In this paper we discuss the construction of the TM110 Mode Cavity. The cavity, based on a superconducting design will be constructed of copper. In addition, the cavity will be cooled with liquid nitrogen to fit within power and mode spacing requirements. The TM110 cavity operating requirements are presented as will the detail of the design, construction, tuning, and commissioning of the TM110 cavity.

• M. Chung
  
• R. C. Davidson, P. Efthimion, E. P. Gilson, R. M. Majeski
  PPPL, Princeton, New Jersey

Installation of a laser-induced fluorescence (LIF) diagnostic system has been completed and initial measurement of the beam density profile has been performed on the Paul trap simulator experiment (PTSX). The PTSX device is a linear Paul trap that simulates the collective processes and nonlinear transverse dynamics of an intense charged particle beam propagating through a periodic focusing quadrupole magnetic configuration. Although there are several visible transition lines for the laser excitation of barium ions, the transition from the metastable state has been considered first mainly because an operating, stable, broadband, and high-power laser system is available for experiments in this region of the red spectrum. The LIF system is composed of a dye laser, fiber optic cables, a line generator, which uses a Powell lens, collection optics, and a CCD camera system. Single-pass mode operation of the PTSX device is employed for the initial tests of the LIF system to make optimum use of the metastable ions. By minimizing the background light level, it is expected that enough signal to noise ratio can be obtained to re-construct the radial density profile of the ion beam.

• M. Dorf
  
• R. C. Davidson, E. Startsev
  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.

• P. Efthimion
  
• R. C. Davidson, E. P. Gilson, L. Grisham
  PPPL, Princeton, New Jersey
• B. G. Logan, P. A. Seidl, W. L. Waldron, S. Yu
  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.

• J. S. Pennington
  
• R. C. Davidson, I. Kaganovich, A. B. Sefkow, E. Startsev
  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.

• A. Shnidman
  
• R. C. Davidson, I. Kaganovich
  PPPL, Princeton, New Jersey

Evaluation of ion-atom charge-changing cross sections is needed for many accelerator applications. The validity of the classical trajectory approximation has been studied by comparing the results of simulations with available experimental data and full quantum-mechanical calculations [1]. Additionally, a theoretical criterion has been developed for the validity of the classical trajectory approximation [2]. For benchmarking purposes, a Classical Trajectory Monte Carlo simulation (CTMC) is used to calculate ionization and charge exchange cross sections for most simple, hydrogen and helium targets in collisions with various ions. The calculated cross sections compare favorably with the experimental results for projectile velocities near the projectile velocity corresponding to the maximum of cross section as a function of projectile velocity. At higher or lower velocities, quantum-mechanical effects become more significant and the CTMC results agree less well with the experimental values of the cross sections.

[1] I. D. Kaganovich, et al., , New Journal of Physics 8, 278 (2006).
[2] Igor D. Kaganovich, et al., Nucl. Instr. and Methods A 544, 91(2005).

• H. Qin
  
• R. C. Davidson, E. Startsev
  PPPL, Princeton, New Jersey

In 3D high-intensity bunched beams, the collective effects associated with strong coupling between the longitudinal and transverse dynamics are of fundamental importance. A direct consequence of this coupling is that the particle dynamics does not conserve transverse energy and longitudinal energy separately, and there exists no exact kinetic equilibrium which has an anisotropic energy in the transverse and longitudinal directions. The strong coupling also introduces a mechanism for the electrostatic Harris-type instability driven by strong temperature anisotropy, which exists naturally in beams that have been accelerated to large velocities. The self-consistent Vlasov-Maxwell equations are applied to high-intensity bunched beams, and a generalized low-noise delta-f particle simulation algorithm is developed for bunched beams with or without energy anisotropy. Systematic studies are carried out that determine the particle dynamics, the approximate equilibrium, and stability properties under conditions corresponding to strong 3D nonlinear space-charge force. Finite bunch-length effects on collective excitations and anisotropy-driven instabilities are also investigated.

• P. Chen
  
• R. Yi, D. Yu
  DULY Research Inc., Rancho Palos Verdes, California

One of the most important targets for building modern particle accelerators is to increase the beam brightness. The purposes of building a dc/rf gun are to seek high bunch charge and low beam transverse emittance, two key parameters for enhancing brightness of accelerators. We present simulation results of the beam emittance changes in a dc/rf gun under different gun voltages. SUPERFISH and PARMELA were used to simulate the beam dynamics in the gun. These simulations indicate that a small beam transverse emittance (< 0.5 mm.mrad) can be obtained when the voltage on the dc gap is lower than 200 kV and the bunch charge is 200 pc, and increments of dc gap voltages will greatly improve the emittances.

• N. Barov
  
• S. Reiche
  UCLA, Los Angeles, California

Many simulation efforts make use of integrated numerical experiments, where the inputs and outputs of several accelerator codes are tied together. This is usually accomplished by writing custom scripts that launch the underlying programs and perform data format translation. We present a way to simplify this process by using a graphical user interface that allows one to describe the data flow in the style of the LabVIEW and Simulink environments. A module to support a new accelerator code involves writing data translators to/from a common format (SDDS or HDF5), and a function to generate an input file based on a standard way of specifying an accelerator lattice (such as Accelerator Markup Language, or AML).

• M. Blaskiewicz
  

A multipurpose coherent instability simulation code has been written, documented, and released for use. TRANFT (tran-eff-tee) uses fast Fourier transforms to model transverse wakefields, transverse detuning wakes and longitudinal wakefields in a computationally efficient way. Dual harmonic RF allows for the study of enhanced synchrotron frequency spread. When coupled with chromaticity, the theoretically challenging but highly practical post head-tail regime is open to study. Detuning wakes allow for transverse space charge forces in low energy hadron beams, and a switch allowing for radiation damping makes the code useful for electrons.

• R. Calaga
  
• R. Tomas, F. Zimmermann
  CERN, Geneva

The tight mechanical aperture for the LHC imposes severe constraints on both the beta and dispersion beating. Robust techniques to compensate these errors are critical for operation of high intensity beams in the LHC. We present simulations using realistic errors from magnet measurements and alignment tolerances in the presence of BPM noise. Correction reveals that the use of BPM calibration and model independent observables are key ingredients to accomplish optics correction. Experiments at RHIC to verify the algorithms for optics correction are also presented.

• A. V. Fedotov
  
• G. I. Bell, D. L. Bruhwiler, A. V. Sobol
  Tech-X, Boulder, Colorado
• I. Ben-Zvi, D. Kayran, V. Litvinenko, E. Pozdeyev
  BNL, Upton, Long Island, New York
• A. O. Sidorin, A. V. Smirnov
  JINR, Dubna, Moscow Region

The traditional electron cooling system used in low-energy coolers employs an electron beam immersed in a longitudinal magnetic field. In the first relativistic cooler, which was recently commissioned at Fermilab, the friction force is dominated by the non-magnetized collisions between electrons and antiprotons. The design of the higher-energy cooler for Relativistic Heavy Ion Collider (RHIC) recently adopted a non-magnetized approach which requires a low temperature electron beam. However, to avoid significant loss of heavy ions due to recombination with electrons in the cooling section, the temperature of the electron beam should be very high. These two contradictory requirements are satisfied in the design of the RHIC cooler with the help of the undulator fields. The model of the friction force in the presence of an undulator field was benchmarked vs direct numerical simulations with an excellent agreement. Simulations of ion beam dynamics in the presence of such a cooler and helical undulator is discussed in detail, including recombination suppression and resulting luminosities.

• A. V. Fedotov
  
• I. Ben-Zvi, D. Kayran, E. Pozdeyev
  BNL, Upton, Long Island, New York
• A. O. Sidorin, A. V. Smirnov
  JINR, Dubna, Moscow Region

The low-energy electron cooling system is based on an electron beam immersed in a longitudinal magnetic field of a solenoid. The coupling of the horizontal and vertical motion allows representation of the friction force as a sum of the transverse and longitudinal components. The analytic treatment proceeds by allowing several approximations, for example, uniform transverse density distribution of electron beam and Maxwellian distribution in the velocity space. The high-energy electron cooling system for RHIC is unique compared to standard coolers. It requires bunched electron beam. Electron bunches are produced by an Energy Recovery Linac (ERL), and cooling is planned without a longitudinal magnetic field. To address the unique features of the RHIC cooler, a generalized 3-D treatment of the cooling force was introduced in the BETACOOL code which allows to calculate the friction force from an arbitrary six-dimensional distribution of the electrons. Results based on this treatment are compared to typical approximations. Simulations for the RHIC cooler based on a realistic electron distribution from the ERL are presented.

• R. P. Fliller
  
• D. A. Edwards, H. Edwards
  Fermilab, Batavia, Illinois
• K. C. Harkay, K.-J. Kim
  ANL, Argonne, Illinois
• T. W. Koeth
  Rutgers University, The State University of New Jersey, Piscataway, New Jersey

The A0 photoinjector is being reconfigured to test the principal of transverse to longitudinal emittance exchange as proposed by Emma et. al., Kim and Sessler, and others. The ability to perform such an exchange could have major advantages to FELs by reducing the transverse emittance. Several schemes to carry out the exchange are possible and will be reported separately. At the Fermilab A0 Photoinjector we are constructing a beamline to demonstrate this transverse to longitudinal emittance exchange. This beamline will consist of a dogleg, and a TM110 5 cell copper cavity followed by another dogleg. The beamline is designed to reuse the bunch compressor dipoles of the photoinjector, along with some existing diagnostics. Beamline layout and optics discussed along with inital data. Future possibilites of performing a similar experiment at the proposed NML facility at Fermilab are also discussed.

• H. Hahn
  
• L. R. Hammons, D. Naik
  BNL, Upton, Long Island, New York

An R&D facility for an Energy Recovery Linac (ERL) intended as part of the 'Electron-Cooling Xperiment' for RHIC is being constructed at this laboratory. The center piece of the project is the experimental 5-cell 703.75 MHz superconducting ECX cavity. Successful operation will depend on effective HOM suppression, and it is planned to achieve HOM damping exclusively with room temperature ferrite absorbers. A ferrite-lined pillbox model with dimensions reflecting the operational unit was assembled, and the cavity resonances and quality factors were determined from scattering coefficient measurements and were interpreted as surface impedance. Results from a 5-cell copper cavity with an attached ferrite absorber prototype are used for the prediction of the ECX cavity HOM damping. A rotational symmetric ferrite-lined pillbox was analyzed theoretically and compared with the simulation codesμWave Studio, GdfidL, and Superfish. Discrepancies of the resonance frequencies and Q-values were found, and steps to reach agreement are discussed.

• D. Kayran
  
• I. Ben-Zvi, R. Calaga, X. Chang, J. Kewisch, V. Litvinenko, E. Pozdeyev
  BNL, Upton, Long Island, New York

Non-magnetized electron cooling of RHIC requires an electron beam energy of 54.3 MeV, electron charge per bunch of 5 nC, normalized rms beam emittance of 4 mm-mrad, and rms energy spread of 3·10^-4 *. In this paper we describe a lattice of a two-pass SCRF energy recovery linac (ERL) and results of a PARMELA simulation that provides electron beam parameters satisfying RHIC electron cooling requirements.

* A. Fedotov, Electron Cooling Studies for RHIC II http://www.bnl.gov/cad/ecooling/docs/PDF/Electron_Cooling.pdf

• D. Kayran
  
• V. Litvinenko
  BNL, Upton, Long Island, New York

A super-conducting RF R&D Energy recovery linac (ERL) is under construction at Brookhaven National Laboratory (BNL). This ERL will be used as a test facility to study issues relevant to high-current, high-brightness beams. One of the goals is to demonstrate an electron beam with high charge per bunch (~ 5 nC) and extremely low normalized emittance (~ 5 mm-mrad) at an energy of 20 MeV. In contrast with operational high-brightness linear electron accelerators, all presently operating ERLs have an order of magnitude larger emittances for the same charge per bunch. One reason for this emittance growth is that the merger system mixes transverse and longitudinal degrees of freedom, and consequently violates emittance compensation conditions. A merger system based on zigzag scheme* resolves this problem. In this paper we discuss performance of the present design of the BNL R&D ERL injector with a zigzag merger.

* V. N. Litvinenko, R. Hajima, and D. Kayran, Nucl. Instr. and Meth. A 557 (2006) 165.

• C. Montag
  

Polarized protons are injected into the Relativistic Heavy Ion Collider (RHIC) just above transition energy. When installation of a cold partial Siberian snake in the AGS required lowering the injection energy by Delta gamma=0.56, the transition energy in RHIC had to be lowered accordingly to ensure proper longitudinal matching. This paper presents lattice modifications implemented to lower the transition energy by ∆ γ_t=0.8.

• E. Pozdeyev
  
• I. Ben-Zvi, A. V. Fedotov, D. Kayran, V. Litvinenko, G. Wang
  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.

• N. Tsoupas
  
• L. Ahrens, K. A. Brown, I.-H. Chiang, C. J. Gardner, W. W. MacKay, P. H. Pile, A. Rusek
  BNL, Upton, Long Island, New York

Uniform irradiation of biological or material samples with charged particle beams is desired by experimentalist because it reduces radiation-dose-errors which are introduced by a non-uniform irradiation of the samples. In this paper we present results of uniform beams produced in the NASA SPACE RADIATION LABORATORY (NSRL) at the Brookhaven National Laboratory (BNL) by a method which was conceived theoretically and tested experimentally at BNL. This method* of producing uniform beams in the transverse beam direction, is based on purely magnetic focusing of the beam and requires no collimation of the beam or any other type of beam interaction with materials. The method is favorably compared with alternative methods** of producing uniform beam distributions normal to the beam direction and can be applied to the whole energy spectrum of the charged particle beams that are delivered by the Booster synchrotron at BNL.

*Uniform Particle Beam Distribution Produced by Octupole Focusing N. Tsoupas et. al. NSE: 126, 71-79 (1997)
**Review of Ion Beam Therapy: Present and Future J. Alonso LBNL EPAC 2000

• N. Tsoupas
  
• L. Ahrens, R. Alforque, M. Bai, K. A. Brown, E. D. Courant, J. Glenn, H. Huang, A. K. Jain, W. W. MacKay, M. Okamura, T. Roser, S. Tepikian
  BNL, Upton, Long Island, New York

The AGS synchrotron employs two partial helical snakes* to preserve the polarization of the proton beam during acceleration in the AGS. The effect of the helical snakes on the beam optics is significant at injection energy, with the effect greatly diminishing early in the acceleration cycle. In order to compensate for the effect of the snakes on the beam optics, we have introduced eight compensation quadrupoles in straight sections of the AGS at the proximity of the partial snakes. At injection the strength of these eight quads is set at a high value but ramped down to zero when the effect of the snakes diminishes. Four of the compensation quadrupoles had to be placed in very short straight sections therefore had to be 'thin' with a length of ~30 cm. The 'thin' quadrupoles were laminated and designed to minimize the strength of the dodecoupole harmonic. The thickness of the lamination was also calculated** to keep the ohmic losses generated by the eddy currents in the laminations below an acceptable limit. Comparison of the measured and calculated harmonics will be presented and the ohmic losses due to the eddy currents, as a function of time during rumping will be discussed.

* H. Huang, et al., Proc. EPAC06, (2006), p. 273.** OPERA computer code. Vector Fields Inc.

• G. Wang
  
• M. Blaskiewicz
  BNL, Upton, Long Island, New York

• M. Conte
  
• A. U. Luccio, W. W. MacKay
  BNL, Upton, Long Island, New York
• M. Pusterla
  Univ. degli Studi di Padova, Padova