05 Beam Dynamics and Electromagnetic Fields

D03 High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling

Paper Title Page
THYM02 Incoherent Effects of Space Charge and Electron Cloud 2942
 
  • G. Franchetti, I. Hofmann
    GSI, Darmstadt
  • F. Zimmermann
    CERN, Geneva
  
  Trapping in, or scattering off, resonances driven by space charge or electron cloud in conjunction with synchrotron motion can explain numerous observations of slow beam loss and emittance growth, which are often accompanied by changes in the longitudinal beam profile. This talk will review recent progress in understanding and modelling the underlying mechanisms, highlight the differences and similarities between space charge and electron cloud, and discuss simulation results in the light of experimental observations, e.g., at GSI, CERN and BNL.  
slides icon Slides  
THPC014 Investigation of Possible CSR Induced Energy Spread Effects with the A0 Photoinjector Bunch Compressor 3005
 
  • R. P. Fliller, H. T. Edwards, G. M. Kazakevich, J. Ruan, R. Thurman-Keup
    Fermilab, Batavia, Illinois
  • T. W. Koeth
    Rutgers University, The State University of New Jersey, Piscataway, New Jersey
  
  The bunch compressor of the A0 Photoinjector at Fermilab was removed this past spring to install a transverse to longitudinal emittance exchange experiment. Prior to its removal questions arose about the possibility of observing the effects of Coherent Synchrotron Radiation on the compressed beam. The energy spread of the beam with and without compression was measured to observe any changes. Various beam charges were used to look for square law effects associated with CSR. No direct observation of CSR was attempted because the design of the vacuum chamber did not allow it. In this paper we report the results of these experiments and comparison with simulations using ASTRA and CSRTrack. The results are compared with analytical approximations. The implications for the ongoing transverse to longitudinal emittance exchange experiment are discussed.  
THPC046 Heating Rate of Highly Space-charge-dominated Ion Beams in a Storage Ring 3080
 
  • Y. Yuri
    JAEA/ARTC, Takasaki
  • H. Okamoto
    HU/AdSM, Higashi-Hiroshima
  
  We investigate the heating process of highly space-charge-dominated ion beams in a storage ring, using the molecular dynamics simulation technique. To evaluate the heating rate over the whole temperature range, we start from an ultra-low-emittance state where the beam is Coulomb crystallized, apply perturbation to it, and follow the emittance evolution. When the ring lattice is properly designed, the heating rate is quite low at ultralow temperature because random Coulomb collisions are suppressed*. It gradually increases after the ordered state is destroyed by perturbation, and comes to a peak when the beam reaches a liquid phase. The dependence of the heating behavior on the beam line density and betatron tune is explored systematically. The effect of lattice imperfection on the stability of crystalline beams is also confirmed.

*J. Wei and A. M. Sessler, EPAC'96, p.1179.

 
THPC084 Studies of Electromagnetic Space-charge Fields in RF Photocathode Guns 3182
 
  • C. S. Park, M. Hess
    IUCF, Bloomington, Indiana
  
  In high-brightness rf photocathode guns, the effects of space-charge can be important. In an effort to accurately simulate the effects of these space-charge fields without the presence of numerical grid dispersion, a Green’s function based code called IRPSS (Indiana Rf Photocathode Source Simulator) was developed*. In this paper, we show the results of numerical simulations of the Argonne Wakefield Accelerator photocathode gun using IRPSS, and compare them with the results of an electrostatic based simulation code. In addition, we show how electromagnetic space-charge fields can affect the designs of photocathode gun magnetic focusing schemes, such as emittance compensation. We will also show how a multipole moment method can be effectively utilized to compute the reflections of electromagnetic space-charge fields due to irises in photocathode guns.

*M. Hess, C. S. Park, and D. Bolton. Phys. Rev. ST Accel. Beams 10, 054201 (2007).

 
THPC085 VORPAL Simulations Relevant to Coherent Electron Cooling 3185
 
  • G. I. Bell, D. L. Bruhwiler, A. V. Sobol
    Tech-X, Boulder, Colorado
  • I. Ben-Zvi, V. Litvinenko
    BNL, Upton, Long Island, New York
  • Y. S. Derbenev
    Jefferson Lab, Newport News, Virginia
  
  Coherent electron cooling (CEC)* combines the best features of electron cooling and stochastic cooling, via free-electron laser technology**, to offer the possibility of cooling high-energy hadron beams with order-of-magnitude shorter cooling times. Many technical difficulties must be resolved via full-scale 3D simulations, before the CEC concept can be validated experimentally. VORPAL is the ideal code for simulating the “modulator” and “kicker” regions, where the electron and hadron beams will co-propagate as in a conventional electron cooling section. Unlike previous VORPAL simulations*** of electron cooling physics, where dynamical friction on the ions was the key metric, it is the details of the electron density wake driven by each ion in the modulator section that must be understood, followed by strong amplification in the FEL. We present some initial simulation results. In particular, we compare the semi-analytic binary collision model with electrostatic particle-in-cell (PIC).

*Ya. S. Derbenev, COOL ’07 Proc. (2007).
**V. N. Litvinenko and Ya. S. Derbenev, FEL ’07 Proc. (2007).
***A. V. Fedotov et al. Phys. Rev. ST/AB 9, 074401 (2006).

 
THPC086 Transverse Mismatch Oscillations of a Bunched Beam in Presence of Space Charge and External Nonlinearities 3188
 
  • C. Benedetti, G. Turchetti
    Bologna University, Bologna
  • G. Franchetti, I. Hofmann
    GSI, Darmstadt
  
  The damping of transverse mismatch oscillations depends on the combined effect of space charge as well as external nonlinearities. Previous studies of this problem for high intensity beams in a synchrotron have not included the combined effect of synchrotron oscillation and external nonlinearities on mismatch. In this paper we explore by 2.5D particle in cell simulations the effect on emittance growth, halo and beam loss caused by space charge, synchrotron oscillation and external nonlinearities. Different tunes are considered in order to understand the importance of external nonlinearities as function of the distance of the working point from the resonance condition.  
THPC087 Electron Traps and Advanced Turbulence Diagnostic 3191
 
  • M. Cavenago
    INFN/LNL, Legnaro, Padova
  • G. Bettega, F. Cavaliere, R. Pozzoli, M. Rome
    INFN-Milano, Milano
  
  In the electron trap Eltrap both trapped and propagating beam (along the magnetic field axis z) up to 20 kV can be studied. Beam structures in x and y (transverse plane) were successfully detected. Main diagnostic and axial control of instabilities was based on electrostatic. The addition of an external electron source, controlled by a laser, makes ns electron bunches now possible. A system to dump the electron beam off axis is also described. Faster diagnostic and control methods can be tested. In particular, Thompson scattering diagnostic of beam structures can be tested, considering that a wavelength shift (even if modest) is present. Nonlinear dynamics modeling of injection process is also described.  
THPC088 Beam Dynamics Simulation of Superconducting HWR Option for the IFMIF Linac 3194
 
  • N. Chauvin, A. Mosnier, P. A.P. Nghiem, D. Uriot
    CEA, Gif-sur-Yvette
  
  One of the requirements of the International Fusion Materials Irradiation Facility (IFMIF) is a 250 mA, 40 MeV cw deuteron beam provided by two 125 mA linacs. In this paper, a design based on superconducting half-wave resonators (HWR) for the 5 to 40 MeV section of the IFMIF driver accelerator is presented. Multi particle beam dynamics simulations have been performed in order to validate the linac design in such a high charge space regime. A Monte Carlo error analysis has been carried out to study the effects of misalignments or field variations. The results of the simulations are presented and the final specifications of the HWR linac are summarized.  
THPC089 Electron-cloud Intrabunch Density Modulation 3197
 
  • G. Franchetti
    GSI, Darmstadt
  • F. Zimmermann
    CERN, Geneva
  
  During the passage of a proton bunch through an electron cloud a complicated electron density modulation arises, with characteristic ring and stripe patterns of high density regions that move radially outward along the bunch. We present simulation results as well as a simple analytical model to reveal the morphology and main features of this phenomenon as well as its dependence on key parameters like bunch length, beam size, and bunch charge.  
THPC091 Experimental Study of an Intense Relativistic Helical Electron Beam Formed with Interception of the Electrons Reflected from the Magnetic Mirror 3200
 
  • E. V. Ilyakov, I. S. Kulagin, S. V. Kuzikov, A. S. Shevchenko
    IAP/RAS, Nizhny Novgorod
  • V. N. Manuilov
    NNGU, Nizhny Novgorod
  
  A new method of formation of pulsed intense relativistic helical electron beams (HEBs) for gyroresonant devices has been presented. The method is aimed at the increase of pitch-factor and the reduction of HEB velocity spread and is intended for use in the formation systems of laminar HEBs characterized by low influence of space charge on their parameters. The method is based on the operation of a special diaphragm located at one of minima of trajectories at the beginning of the transportation channel. The diaphragm diameter is chosen so that the electrons with the lowest oscillatory velocities cannot bend round the diaphragm and settle on it. The rest electrons pass by moving in the increasing magnetic field. Then, the electrons with the greatest oscillatory velocities are adiabatically reflected from the magnetic mirror between the electron gun and the transportation channel and settle on the back of the same diaphragm. Reduction of space charge of the reflected electrons has led to the increase of HEB pitch-factor (HEBs have been formed with the record of pitch-factors exceeding 2), while the accumulation of space charge worsens the HEB provoking modulation of formed HEB current.  
THPC097 A Full Analytical Method to Determine Equilibrium Quantities of Mismatched Charged Particle Beams evolving in Linear Channels 3203
 
  • R. P. Nunes, F. B. Rizzato
    IF-UFRGS, Porto Alegre
  
  The focus of this work is to show a full analytical expression to determine relevant equilibrium quantities of a magnetically focused and high-intensity charged particle beam when evolving in a linear channel. Through the current approach, some intermediate steps of our original hybrid model which have to be solved numerically now can be eliminated, leading to the obtainment of a full analytical expression. This expression relates initial beam parameters with those obtained at equilibrium, allowing that the fraction of halo particles f can be evaluated. As a consequence, through the developed model, beam quantities like the envelope and emittance can be naturally determined. This is important in the accelerator engineering, since halo characteristics is a factor to be considered in the design of its confinement structure. For validation, full self-consistent N-particle beam numerical simulations have been carried out and its results compared with the predictions supplied by the full analytical model. The agreement is shown to be nice as with the simulations as with the hybrid numerical-analytical version of the model.  
THPC098 Halo characterization of initially mismatched beams through phase-space modeling 3206
 
  • R. P. Nunes, F. B. Rizzato
    IF-UFRGS, Porto Alegre
  
  This work discusses a method of characterizing the beam particles with just some assumptions about the entire beam phase-space topology. At equilibrium, the beam phase-space can be recognized as composed by almost two distinct regions: a thin horizontal branch over the r axis that is populated by the core particles and a curve branch in the dr/ds x r plane, which is populated by the halo particles. Since these regions have a regular shape, then it is readily possible to convert them to an analytical expression. Two distinct shapes have been employed (circular and elliptical) to model the beam halo branch. With this, all usual initial beam mismatch values are covered with accuracy to determine the beam envelope and emittance at equilibrium. Full self-consistent N-particle beam simulations have been carried out and its results compared with the ones obtained with the model. Results agreed nice for all analyzed mismatch cases.  
THPC100 Collisionless Relaxation in the Transport of Space Charge Dominated Beams 3209
 
  • R. Pakter, Y. Levin, T. N. Teles
    IF-UFRGS, Porto Alegre
  
  Relaxation to a final stationary state of particles interacting through long-range forces, such as Coulomb, is intrinsically different than that of systems with short-range interactions. While in the latter case it is known that the interparticle collisions drive the system to an equilibrium Maxwell-Boltzmann distribution, in the former case, the collision duration time diverges and the state of thermodynamic equilibrium is never reached. In this paper, a theory is presented which allows to quantitatively predict the final stationary state achieved by a transported space-charge dominated beam during a process of collisionless relaxation*. It is shown that a fully matched beam relaxes to a Fermi-Dirac distribution. However, when a mismatch is present and the beam oscillates, halo formation leads to a phase separation. The theory developed allows to quantitatively predict both the density and the velocity distributions in the final stationary state, including the halo.

* Y. Levin, R. Pakter, and T. N. Teles, Phys. Rev. Lett., 100, 040604 (2008).

 
THPC101 Transverse Schottky Noise and Beam Transfer Functions with Space Charge 3212
 
  • S. Paret, O. Boine-Frankenheim, V. Kornilov
    GSI, Darmstadt
  • T. Weiland
    TEMF, Darmstadt
  
  The heavy ion synchrotron SIS18 will serve as booster for the synchrotron SIS100 to be built as part of the Facility for Antiproton and Ion Research (FAIR). As such the SIS18 should accelerate ion beams with a factor of 10-100 higher intensity, compared to the present performance. Beams of such intensities may suffer instabilities due to collective effects. Particularly at injection-energy space charge and the resistive wall impedance will affect the beam remarkably. Experiments for the investigation of direct space charge were performed in SIS18. Transverse Schottky signals and beam transfer functions (BTF) of coasting ion beams affected by space charge were measured. A distortion of the Schottky bands and BTF was observed and compared to a simple model allowing for linear space charge. The model reproduced the deformation and yielded parameters of the beam.  
THPC102 Image Simulations on the ISIS Synchrotron 3215
 
  • B. G. Pine, C. M. Warsop
    STFC/RAL/ISIS, Chilton, Didcot, Oxon
  
  ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on a loss-limited 50 Hz proton synchrotron, which accelerates ~3·1013 ppp from 70 to 800 MeV, corresponding to mean beam powers of 0.2 MW. A significant proportion of beam loss is attributable to space charge effects. One such effect is the image field which forms in the beam pipe. Off-centre beams resulting from closed orbit errors generate fields, which can perturb the beam and cause loss. Of particular interest on ISIS is the rectangular, varying aperture, vacuum vessel, as compared with the more usual constant aperture circular or elliptical geometries. A new 2D space charge code, Set, was developed to study these effects. The code simulates the effects of space charge using a 2D particle-in-cell model of the beam distribution, including an appropriate treatment of the rectangular beam pipe, and details of the ISIS lattice. The effects of images on closed orbits, driving terms, and the evolution of beam distributions at ISIS operational intensities were explored.  
THPC103 Wave Breaking and Test Particle Dynamics in Inhomogeneous Beams 3218
 
  • F. B. Rizzato, Y. Levin, R. P. Nunes, R. Pakter, E. G. Souza
    IF-UFRGS, Porto Alegre
  
  This work analyzes the dynamics of inhomogeneous, magnetically focused high-intensity beams of charged particles. While for homogeneous beams the whole system oscillates with a single frequency, any inhomogeneity leads to propagating transverse density waves which eventually result in a singular density build up, causing wave breaking and jet formation. Wave breaking is shown to relax the mismatched beam and we make use of Lynden-Bell's theory of violent relaxation to estimate characteristics of the relaxed state.  
THPC104 Optical Diagnostic on Gabor Plasma Lenses 3221
 
  • K. Schulte, M. Droba, O. Meusel, U. Ratzinger
    IAP, Frankfurt am Main
  
  Gabor lenses have been built and successfully been used for the focussing of particle beams. In the case of a positive ion beam the space charge of the confined electron cloud may cause an over compensation of the ion beam space charge force and consequently focus the beam. The nonneutral plasma (NNP) is influenced by the external fields and its current state can be determined by the beam emittance growth. Experiments using a high field Gabor lens have shown a correlation between the thermalization of the enclosed electron cloud and the focussing quality. A three segmented Gabor lens was constructed recently for a more detailed investigation of the plasma parameters as a function of the external fields. The commissioning of the lens has been finished successfully and the light emitted by the interaction between the electron cloud and the residual gas has been observed. In a next step the experiments will concentrate on the spectral analyses of the emitted light to evaluate the temperature and density distribution of the confined NNP. Experimental results will be presented in comparison with numerical simulation.  
THPC105 Self-consistent Transverse Dynamics and Interbunch Energy Exchange in Dielectric Loaded Wakefield Accelerating Structures 3224
 
  • I. L. Sheynman
    LETI, Saint-Petersburg
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio
  
  The self-consistent transverse dynamics of high current relativistic electron beams used for generating wakefields in dielectric loaded structures is investigated. The primary application of this work is to multi-bunch wakefield acceleration. The maximum distance the high current beam can travel through the structure in the absence of focusing without experiencing beam breakup and the energy transferred to the accelerated electron bunch will be presented. We consider both ramped and uniform charge distributions in the sequence of high current drive bunches. The ramped drive charge distribution is compared to the case of a uniform charge distribution in terms of the requirements for the beam focusing system and the effectiveness of the energy transfer to the accelerated electron bunch.  
THPC107 Beam Dynamical Issues of the KEK All-ion Accelerator 3227
 
  • K. Takayama, T. Adachi, E. Nakamura, H. Someya
    KEK, Ibaraki
  
  R&D works to realize an all-ion accelerator (AIA)* capable of accelerating all species of ions with any possible charge state, based on the induction synchrotron concept, which was demonstrated using the KEK 12 GeV-PS in 2006**, are going on at KEK. The KEK AIA, which is a modification of the existing KEK 500 MeV Booster Ring of a rapid cycle synchrotron, may be an injector-free accelerator. An ion beam from the high-voltage terminal of 200 kV is directly injected into the accelerator ring. Several key issues associated with the low energy injection must be addressed. Space-charge limited current due to a small relativistic b and a short life-time due to scattering with the residual molecules and eddy-current induced magnetic fields associated with guide-fields ramping from a low field level are among them. Careful considerations on them suggest that there are significant constrains on the operational performance and gives achievable beam parameters assuming the present parameters of the KEK AIA.

*K. Takayama, Y. Arakida, T. Iwashita, Y. S himosaki, T. Dixit, K. Torikai, J. of Appl. Phys. 101, 063304 (2007).
**K. Takayama et al., Phys. Rev. Lett. 98, 054801 (2007).

 
THPC108 Observation of Bound States of Particles in the Storage Ring 3230
 
  • A. S. Tarasenko, I. S. Guk
    NSC/KIPT, Kharkov
  
  The deviation of n-particle state lifetime from the law T1/n, where T1 is a mean lifetime of one particle, in the storage ring was experimentally observed. Authors relate this deviation to interaction between the particles, conditioned by the fields directed in passive resonant devices of vacuum chamber of the storage ring. Depending on type of connection of the beam with passive resonant device, the interaction can be repulsive or attracting. The binding energy of a pair of particles for a case of their effective attraction is calculated.  
THPC110 Investigation of Helical Cooling Channel 3233
 
  • K. Yonehara, V. Balbekov
    Fermilab, Batavia, Illinois
  
  A helical cooling channel (HCC) has been proposed to quickly reduce phase space of muon beams*. It is composed of solenoidal and helical coils to provide focusing and dispersion needed for the six-dimension cooling. A comprehensive investigation of the HCC is performed in presented work including theoretical analysis, particle tracking and Monte Carlo simulation. These results are also compared with the past simulation results** to confirm the helical cooling theory. Optimization of the channel and estimation of its ultimate performances are presented.

*Y. Derbenev and R. P. Johnson. PRSTAB 8, 041002 (2005).
**K. Yonehara et al. TPPP052, Particle Accelerator Conference 2005.

 
THPC111 Simulation ofμBunching Instability Regimes in the FLASH Bunch Compressors 3236
 
  • M. Vogt, T. Limberg
    DESY, Hamburg
  • D. H. Kuk
    The University of Texas at Austin, Austin, Texas
  
  The bunch compression scheme for the European XFEL will operate in a regime in which, at least without additional energy spread introduced by a laser heater, theμbunching effect proposed in the literature may severely degrade the performance of the FEL. However, clear, unambiguous signals of theμbunching effect have not yet been seen neither in simulation nor experiment. The proposedμbunching effect amplifies initial current modulations by interleaved application of longitudinal collective energy kicks and transformations of energy modulation into current modulation in magnetic chicanes. In order to establish a parameter regime for experimental verification ofμbunching at the FLASH VUV-FEL at DESY, we have scanned the relevant part of the parameter space using a linear, quasi-analytic, noise-free gain-model and complemented this with particle tracking simulations. The tracking was performed using interleaved runs of ASTRA for acceleration modules and CSRTrack for the chicanes, automatically linked by the start-to-end simulation tool box Gluetrack.  
THPC112 KONUS Dynamics and H-mode DTL Structures for EUROTRANS and IFMIF 3239
 
  • C. Zhang, M. Busch, H. Klein, H. Podlech, U. Ratzinger, R. Tiede
    IAP, Frankfurt am Main
  
  During the last two decades, the combination of the KONUS beam dynamics and H-mode DTL structures has been developed as an efficient solution for accelerating low- and medium-energy proton and ion beams. EUROTRANS is a EUROpean Research Programme for the TRANSmutation of High Level Nuclear Waste in an Accelerator Driven System. IFMIF is a planned International Fusion Material Irradiation Facility to test materials for fusion reactors. For the driver linacs of both projects, two H-DTLs have been proposed to cover the energy ranges of 3–17MeV and 5–40MeV, respectively. The beam dynamics designs as well as the error studies of the H-DTLs are presented in this paper.  
THPP089 Gamma Transition Jump for PS2 3572
 
  • W. Bartmann, M. Benedikt, E. Métral, D. Möhl
    CERN, Geneva
  • S. Peggs
    BNL, Upton, Long Island, New York
  
  The PS2, which is proposed as a replacement for the existing ~50-year old PS accelerator, is presently considered to be a normal conducting synchrotron with an injection kinetic energy of 4 GeV and a maximum energy of 50 GeV. One of the possible lattices (FODO option) foresees crossing of transition energy near 10 GeV. Since many intensity dependent effects can take place in both the longitudinal and the transverse planes a fast jump of gamma transition is necessary in order to pass the non-adiabatic region rapidly. The aim of the present paper is on the one hand to scale the gamma transition jump, used since 1973 in the PS, to the projected PS2 and on the other hand based on these results the analysis of the implementation and feasibility of a gamma transition jump scheme in a conventional FODO lattice.