Title: Unexpected Results on Microwave Waveguide Mode Transmission
Measurements in the SPS Beam-pipe
F. Caspers, CERN, T. Kroyer, TU Vienna and CERN
In order to measure the electron cloud density, a microwave transmission measurement was set up over 30m in the SPS beam-pipe. The use of TE waveguide modes eliminates direct interaction with the highly relativistic beam. An electron cloud present in the beam-pipe should lead to a small phase shift of the CW microwave signal. Since this phase shift is modulated by the bunch revolution frequency it translates to a phase modulation which can be measured. However, defying all expectations, a huge beam-induced signal attenuation was found which cannot be understood by current electron cloud models. This attenuation showed strongly fluctuating memory effects of the order of microseconds after the passage of a batch or single bunch. Both effects are present for a wide range of microwave signal frequencies and beam parameters. Models to possibly explain this effect are discussed.
Route de Meyrin CH-1211 Geneva 23
Title: Prediction of Electron Cloud Effects in the Synchrotron Light
Source PETRA III
R. WANZENBERG, DESY, Hamburg, Germany
At DESY it is planned to convert the PETRA ring into a synchrotron radiation facility, called PETRA III, in 2007. The computer code ECLOUD has been used to simulate electron cloud effects for different operation modes of PETRA III for the option to use positrons to generate the synchrotron radiation. The density of the electron cloud has been calculated for different beam and vacuum chamber material parameters. It is found that estimates of the electron cloud density from the condition of neutrality are in quite good agreement with the simulation results. An effective transverse single bunch wakefield due to the electron cloud has been obtained from a broad band resonator model. Based on this model it has been found that no single bunch instability due to electron clouds is expected for PETRA III.
Notkestr. 85, 22603 Hamburg, Germany
Title: Review of Single-Bunch Instabilities Driven by an Electron
Frank Zimmermann, CERN
Electrons generated and accumulated inside the beam pipe form an ‘electron cloud’ that interacts with a charged particle beam. If the number of electrons is sizable, this beam-cloud interaction can give rise to a two-stream instability, resulting in beam loss or emittance growth. The instability can occur within a single bunch, e.g., passing through the cloud on successive turns in a storage ring, or it can be a multi-bunch instability, where the motion of successive bunches is coupled via the electron cloud. In this talk, I review the experimental evidence, simulation approaches and analytical treatments of single-bunch two-stream instabilities caused by an electron cloud. Depending on the parameter regime, this type of instability may resemble a coasting-beam instability, classical beam break-up, or transverse-mode coupling. It can also cause long-term emittance growth. Despite of the apparent similarities, a few fundamental differences distinguish the two-stream instability from a conventional impedance-driven instability, and limit the applicability of established accelerator-physics concepts, like ‘wake field’. On the other hand, if, in addition to the electron cloud, space-charge forces, conventional impedance, or beam-beam interaction are also present, these can conspire so as to enhance the growth rate.
Route de Meyrin, CH-1211 Geneva 23
Title: Electron clouds and vacuum pressure rise in RHIC
Institute: Brookhaven National Lab
Wolfram Fischer, Brookhaven National Lab
The luminosity in RHIC is limited by a vacuum pressure rise in the warm regions, observed with high intensity beams of all species (Au, p, d). At injection, the pressure rise could be linked to the existence of electron clouds. In addition, a pressure rise in the experimental regions may be caused by electron clouds, and lead to an increased background. We review the existing observation, comparisons with simulations, as well as corrective measures taken and planned.
Bldg. 911B Upton, NY 11973
Title: Simulation of electron cloud build-up in the ISIS proton
synchrotron and related machines.
Institute: Rutherford Appleton Laboratory, Accelerator Science and Technology Centre
Electron cloud formation and the associated effects of beam loss and
instabilities have been observed in high intensity proton machines such as the
LANL PSR and the CERN SPS. A program has recently been launched at the
Rutherford Appleton Laboratory (UK) to understand the lack of electron cloud
induced instabilities in the operations of the 160 kW 70-800 Mev ISIS
synchrotron.Simulations have been carried out using a newly developed version of
the CERN ECLOUD code [1,2] to model the main features of the electron cloud
build-up in a representative field free region of the ISIS ring. A
comparative study has also been undertaken to gauge e-p related
problems/limitations in possible future proton machines for spallation neutron
sources (ESS) or neutrino factories (ISIS MW upgrade).
 F. Zimmermann, "A simulation study of electron-cloud instability and beam induced multipacting in the LHC", LHC-Project-Report 95 (1997).  F. Zimmermann, "Electron cloud simulations for SPS and LHC", Chamonix X, CERN-SL-2000-007 (2000).
Bldg R2, 4.05 Rutherford Appleton Laboratory Chilton, Didcot Oxon OX11 0QX England (UK)
Title: Electron cloud effects in the KEKB LER
H. Fukuma, KEK
A vertical beam blowup, which is explained by a head-tail instability caused by an electron cloud, has been an important issue to limit the luminosity in the KEK B factory. Although the blowup is much suppressed by solenoids installed around the ring it is still observed if the average line charge density of the beam exceeds about 5nC/m. Thus the blowup is still an issue for the luminosity upgrade. The electron cloud causes not only the blowup but also a betatron tune shift and a coupled bunch instability which give information of the electron cloud. We review experimental studies of the electron cloud effects in the KEKB Low Energy Ring (LER). The paper will cover the effect of the solenoids on the blowup, the tune shift caused by the electron cloud, an attempt to detect head-tail motion by a streak camera, the coupled bunch instability caused by the electron cloud and so on.
High Energy Accelerator Research Organization (KEK), Oho 1-1, Tsukuba, Ibaraki, Japan
Title: The Electron Cloud Instability Studies in the BEPC
Institute: Institute of High Energy Physics
J.Q. Wang, Z.Y. Guo, Y.D. Liu, Q. Qin, J. Xing, Z. Zhao Institute of High Energy Physics
The ECI in the BEPC was studied with experiments and simulations in recent years. Several electron cloud detectors have been installed into the BEPC storage ring to study the electron yielding. The effect of the solenoid on ECI, and the effect of the clearing electrode on ECI have been observed in BEPC experimentally. To evaluate the ECI in BEPCII, the upgrade project of BEPC, a computer code has been developed to simulate the electron density in the antechamber under different conditions, as well as the progress of the single bunch and coupled bunch instabilities caused by the electron cloudy. Experiment is also being planed to study the possibility to clear the electron cloud by putting voltages on all of the BPM buttons on BEPC. The experimental and simulation results, as well as the activities are reported in this paper.
Beijing 100039, P.R. China
Title: Electron-Cloud Effects in the TESLA and CLIC Positron Damping
F. Zimmermann, CERN, Geneva, Switzerland R. Wanzenberg, DESY, Hamburg, Germany
Damping rings are necessary to reduce the emittances by the particle sources to the small values required for the linear collider. Electron cloud effects in such a damping ring can cause transverse single bunch instabilities leading finally to an emittance blow up. The density of the electron cloud has been calculated for the beam and vacuum chamber parameters of the TESLA and CLIC damping ring. The arc and the damping wiggler section have been studied separately. For the TESLA dog-bone ring also the electron cloud in the long straight section has been investigated. An effective transverse single bunch wakefield due to the electron cloud has been obtained and a first assessment was made of the resulting single-bunch instabilities.
Notkestr. 85 22603 Hamburg Germany
Title: Simulation of Transverse Single Bunch Instabilities and
Emittance Growth caused by Electron Cloud in LHC and SPS.
Institute: DENER & INFM, Politecnico di Torino, Italy, & CERN
Elena Benedetto, DENER & INFM, Politecnico di Torino, Italy and CERN; D. Schulte, F. Zimmermann, CERN; G. Rumolo, GSI
The electron cloud may cause transverse single-bunch instabilities in proton beams such as those in the LHC and the CERN SPS. These instabilities and the consequent emittance growth are simulated by the HEADTAIL code with conducting boundary conditions. The sensitivity of the simulation results to several numerical parameters is studied by varying the number of interaction points of the bunch with the cloud, the phase advance between subsequent interaction points and the number of macroparticles used to represent the protons and the electrons. Simulations for the SPS, including a transverse feedback system and a dipole magnetic field, are compared with machine observations. The effects of a large chromaticity on the instability evolution are also investigated for both SPS and LHC, considering various levels of electron cloud density.
Route de Meyrin CH-1211 Geneva 23
Title: Instability dynamics with electron cloud buildup in long
Michael Blaskiewicz, BNL C-AD
For long bunches, trailing edge multi-pacting causes the electron cloud density at the trailed edge of the bunch to be significantly larger than the cloud density during the early and central portions of the bunch. Simulations including this effect are presented and compared with data and simulations without multipacting.
BNL 911B Upton NY 11973-5000
Title: Overview and Actual Understanding of the Electron Cloud Effects
and Instabilities in Future Linear Colliders
Mauro Pivi, SLAC
In the beam pipe of the of a linear collider, ionization of residual gasses, photoemission and secondary emission may lead to amplification of an initial electron signal during the bunch train passage and ultimately give rise to an electron-cloud. We present recent computer simulation results for the main features of the electron cloud generation in the GLC/NLC main DR and for the TESLA DR. We estimate the secondary electron yield thresholds for the development of the electron cloud in the arcs of the damping rings and present also results for a high electron reflectivity model. Fast Head-Tail and coupled-bunch instability thresholds are also calculated for the NLC main DR. The results are obtained by the computer simulation codes HEAD-TAIL and POSINST, which were developed to study the electron cloud effect in particle accelerators.
2575 Sand Hill Road, MS 66 Menlo Park, CA-94025
Title: Solenoid effects on electron cloud
L. Wang (BNL, Upton, New York, USA) S. Kurokawa, S.S. Win (KEK, Tsukuba, Japan) A. Chao (SLAC, Menlo Park, California,USA)
Electron cloud due to beam-induced multipacting can cause transverse instabilities and beam size blow-up in positron and proton accelerators. Solenoid is one good remedy to suppress the multipacting in drift region by confining the electrons to near the wall surface. There is a long drift region in KEKB LER, where most of the beam pipe in drift region is occupied by solenoid. The solenoid effect on electron cloud build-up, wakefield and transverse coupled instabilities are investigated in this paper.
building 817, BNL, Upton, NY, 11973-5000
Title: Energy structure of electron cloud
L. Wang, BNL, Upton,, New York, USA A. Chao, SLAC, Menlo Park, California, USA
The transverse beam instability and beam size blow-up caused by electron cloud become increasingly important in high intensity accelerators. The electron cloud builds up through beam-induced multipacting. This paper investigates the energy spectrum of the electron cloud using particle simulation. A "stop-band structure" is found and a model is suggested to explain and to describe this phenomenon. The electron energy spectrum is very useful information for the understanding of multipacting and the electron cloud effects.
building 817, BNL, Upton, NY, 11973-5000
Title: The CMEE Library for Numerical Modeling of Electron Effects
Institute: Tech-X Corp.
Peter Stoltz, Tech-X Corp. Seth Veitzer, Tech-X Corp. Ron Cohen, LLNL Art Molvik, LLNL Miguel Furman, LBNL Jean-Luc Vay, LBNL
The CMEE (Computational Modules for Electron Effects) library is a collection of computer routines for numerical modeling of electron effects in accelerator and plasma physics codes. The goal of this library is to make these numerical models available to any code in need of electron effects modeling by making the library routines independent of computer language and platform. CMEE includes routines to model secondary electrons, neutral gas desorption and ionization. The secondary electron routines are based on routines from the POSINST code. The ionization routines are based on the IONPACK library from Tech-X. This talk will discuss the latest state of these routines, specifically implementation in the WARP code and comparisons to data from the High Current Experiment (HCX).
5621 Arapahoe Ave, Suite A, Boulder, CO, 80303
Title: Beam observations with electron cloud in the CERN-PS&SPS
Institute: CERN - AB Department
Gianluigi Arduini, CERN
With the start of the machine studies to characterize the behaviour of the LHC beam in the SPS in 1999, it became evident that electron multipacting was occurring in the SPS vacuum chambers in the presence of this beam. Electron multipacting induces dramatic pressure increases preventing stable operation, it limits the performance of the beam instrumentation and of the high voltage electrostatic devices (e.g. electrostatic septa) and induces strong transverse instabilities leading to emittance dilution. Although a reduction of the Secondary Emission Yield can be obtained by beam conditioning, multipacting persists in the arcs for the nominal LHC bunch population and electron cloud instabilities remain an issue for the LHC beam. A programme of studies has been launched since 1999 to study the electron cloud instability in the SPS and in the PS for the LHC and fixed target beams. The experimental tools and analysis developed so far are presented together with the results of the observations. The countermeasures applied in the PS Complex & SPS against the electron cloud instability are also discussed.
1211 Geneva 23 Switzerland
Title: Experimental studies of electron and gas sources in a heavy-ion
A. W. MOLVIK, F.M. BIENIOSEK, R.H. COHEN, S. EYLON, A. FALTENS, A. FRIEDMAN, E. HENESTROZA, M. KIREEFF COVO, J.W. KWAN, S.M. LUND, L. PROST, P.K. ROY, P.A. SEIDL, J-L. VAY, G. WESTENSKOW, S. YU, HIF-VNL
Electron cloud effects, ECEs, are normally a problem only in ring accelerators. However, as we will discuss, heavy-ion induction linacs for inertial fusion energy have an economic incentive to fit beam tubes tightly to intense beams. This places them at risk from electron clouds produced by emission of electrons, and ionization of gas, from walls. We have measured electron and gas emission from 1 MeV K+ impact on surfaces near grazing incidence on the High-Current Experiment (HCX) at LBNL and are making similar measurements below 500 KeV on the injector test stand STS-500 at LLNL. Electron emission scales with 1/cos consistent with emission from a thin layer, whereas gas desorption varies much more slowly with angle indicating sources other than adsorbed gas layers. Mitigation techniques are being studied: A bead-blasted rough surface reduces electron emission by a factor of 10 and gas desorption by a factor of 2. A biased cylindrical mesh on the Neutralized Transport Experiment (NTX) at LBNL prevents electron emission from the beam-tube. We are installing diagnostics on HCX, between and within quadrupole magnets, to measure the beam halo loss, net charge and expelled ions, from which we will infer gas density, electron trapping, and the effects of mitigation techniques. We have also installed clearing electrodes between magnets to remove electrons, and a suppressor electrode after the magnets to block secondary electrons off the end wall from entering the magnets. The effects of electrons on ion beams are determined with slit scanners. These data will be compared with predictions of theory and simulations. * Work performed for the USDOE by LLNL under Contract W-7405-ENG-48, and by LBNL under Contract DE-AC03-76F00098.
L-637, LLNL Livermore, CA 94550 USA
Title: Suppression of the effective SEY for a grooved metal surface
G. Stupakov and M. Pivi, SLAC
We have studied the secondary electron emission from a metal surface with a grooved profile. Secondary electrons emitted from the grooved surface are likely to hit other wall of the groove causing a partial trapping of electrons which results in a suppression of the effective secondary emission yield (SEY). However, grooves also introduce a possibility of grazing incidence events which increase the SEY. To analyze both effects, as well as the significance of higher generations of secondaries, we have carried out numerical simulations using a model for the secondary emission developed previously by M. Furman and M. Pivi (PRSTAB, vol. 5, 124404, 2002). We have studied triangular and rectangular shapes of the grooves and calculated the effective SEY as a function of the geometrical parameters of the grooves. The proposed mechanism of SEY reduction might be important for suppression of multipacting in particle accelerators.
2575 Sand Hill Road Menlo Park, CA, 94025
Title: Delta-f Simulations of Electron-Ion Two-Stream Instability
Institute: Princeton Plasma Physics Laboratory, Princeton University
Hong Qin, Ronald C. Davidson, and Edward A. Startsev, Princeton Plasma Physics Laboratory, Princeton University
Two-stream instabilities in intense charged particle beams, described self-consistently by the nonlinear Vlasov-Maxwell equations, are studied using a 3D multispecies perturbative particle simulation method. The beam equilibrium, stability, and transport (BEST) code is used to simulate the linear and nonlinear properties of the electron-proton (e-p) two-stream instability observed in the Proton Storage Ring (PSR) experiment as well as the electron-ion two-stream instability in the high intensity ion beams for heavy ion fusion drivers. Simulations show that the electron-ion instability has a typical dipole-mode structure, and that the instability threshold descreases with increasing fractional neutralization, and increases with increasing axial momentum spread of the beam particles. In the nonlinear phase, the simulations show that the instability first saturates at a relatively low level, and subsequently grows to a higher level. The nonlinear space-charge-induced transverse tune spread, which introduces a major growth-rate reduction effect on the instability, is studied for the self-consistent equilibrium populations of ions and electrons. Initial results on the two-stream instability for bunched beams and the interaction between the instability and the secondary electron yield will also be discussed.
Research supported by the U.S. Department of Energy.
Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543, USA
Title: Correlation of Pressure Rise and Experimental Backgrounds at
RHIC in Run04.
A. Drees, BNL U. Iriso-Ariz, BNL W. Fischer, BNL
At RHIC, high intensity heavy ion beams, as achieved in the FY 2004 run, cause pressure rises in the experimental areas. Electron clouds could be responsible for this rise. However, the evolution of the pressure and therefore the background, varies significantly between the different Interaction Regions. At this point, the sustainable background levels limit the achievable luminosity for RHIC. In addition, the bad background conditions degrade the data quality for the experiments and increase the number of false triggers. Experimental data will be presented and compared to expectations. our Abstract
BNL C-A Department, Building 911-b Upton, NY 11973
Title: Suppression of the beam instability related to electron cloud
at PEP-II B-factory.
Institute: Stanford Linear Accelerator Center
Artem Kulikov SLAC
PEP-II B-factory operates at a record high circulated currents - ~2.2 A in the positron ring. Electron cloud effects became apparent when the positron ring current reached ~ 0.7 A. Electron cloud was a significant factor limiting collider luminosity. To suppress electron cloud related beam instabilities solenoids covering ~80% of the ring circumference had been installed. Experimental data related to the electron cloud effects in PEP-II will be presented.
2575 Sand Hill Road Menlo Park, CA 94025
Title: Experimental and Simulation Studies of Electron Cloud
Multipacting in the Presence of Small Solenoidal Fields.
A. Novokhatski, A.Kulikov, J.Seeman SLAC
The SLAC PEP-II B-factory operates at high electron and position currents. To damp the transverse instability initiated by the electron cloud a solenoidal magnetic field was placed in the positron ring. Solenoid sections of approximately 5 m long are connected in series with individual power supplies. Study of the electron cloud behavior was performed in a short solenoid section. Simulation studies were carried out in order to determine the secondary emission parameters from experimental measurements.
2575 Sand Hill Rd, Menlo Park, CA 94025, USA
Title: Use of maps for exploring electron cloud parameter space
Institute: Brookhaven National Laboratory
Ubaldo Iriso, Steve Peggs / BNL
The optimal distribution of the bunch pattern around the RHIC circumference is studied to decrease the electron density for a fixed total beam current. In the search for a bunch pattern that minimizes this density, we show that, for typical parameters, the bunch-to-bunch evolution of the electron cloud density can be represented by a cubic map. Furthermore, we discuss the use of linear bunch-to-bunch maps for small electron cloud densities. The linear coefficients evaluate the electron cloud stability for a given set of physical parameters (bunch charge, SEY, et cetera). Thus, the use of (linearized) maps frees up the slow but detailed simulation codes to explore parameter space, when studying the increase (to a saturated value) or disappearance of the electron cloud under alternative bunch patterns.
Bg 911B, C-AD Upton, NY 11973 (USA)
Title: Analysis of the Electron Pinch during a Bunch Passage
Institute: DENER & INFM, Politecnico di Torino, Italy, & CERN
Benedetto Elena, DENER & INFM, Politecnico di Torino, Italy, and CERN; F. Zimmermann, CERN
We present an analytical calculation of the electron density evolution during the passage of a proton bunch through an electron cloud, considering a circular symmetry and a linear transverse force. From the electron density, computed for various longitudinal beam distributions, we then infer the average tune shift and the incoherent tune spread inside the bunch. The analytical results are compared with computer simulations, by which we can also extend the study to non-uniform, e.g. Gaussian, transverse beam profiles, which give rise to non-linear forces on the electrons.
Route de Meyrin CH-1211 Geneva 23
Title: Measurements on a horizontal instability in DAFNE positron ring
Institute: Istituto Nazionale di Fisica Nucleare - Lab.Naz. di Frascati
A.Drago, M.Zobov, - INFN/LNF - Italy
During the year 2003, a strong horizontal multibunch instability was limiting the positron beam current at level of ~450mA. The authors have done measurements to study the instability by tracking the transverse displacements for each bunch on turn-by-turn basis. Switching off the horizontal feedback for short periods, we have performed transverse grow-damp measurements suitable to estimate the instability growth rates (as well as the feedback damping rates) for each bunch at different beam currents and to evaluate the tune shift along the bunch train. In particular, a strong dependence of oscillation amplitudes on the bunch relative position in the train has been revealed. In this paper we describe the apparatus for multibunch oscillation amplitude tracking, discuss the transverse feedback performance and summarize some observations on the horizontal instability.
Via E.Fermi, 40 I-00044 Frascati (RM) - ITALY
Title: Surface related properties as an essential
ingredient to e-cloud simulations.
Institute: LNF-INFN I-00044 Frascati
R. Cimino, - INFN/LNF - Italy
Via E.Fermi, 40 I-00044 Frascati (RM) - ITALY
Title: E-cloud simulations for DAFNE
C. Vaccarezza (a), G. Bellodi (b), G. Rumolo(c), F. Zimmermann(d), R. Cimino (a). (a) LNF-INFN, Italy; (b) RAL, United Kingdom (c) GSI, Germany, (d) CERN, Switzerland
In the early commissioning of the DAFNE e+e- collider preliminary simulations have predicted significant e-cloud induced beam instabilities in the positron ring for the design machine parameters. Such calculations were not refined to simulate e-cloud instabilities using more realistic parameters (i.e. chamber geometry, measured SEY and actual beam conditions) while DAFNE, on the other hand, has been routinely operated with more than 1A of circulating positron current, without clear evidence of the predicted e-cloud limitations. In this work we use the more recently developed computer codes to simulate e-cloud build-up at DAFNE to evaluate their validity to predict the observed behavior, and to extrapolate it to higher currents and/or different bunch spacing. In this framework, the role played by the approximations used to describe the machine geometry and the material behavior is discussed.
Via E. Fermi 40 I-00044 Frascati
Title: Status report on the merging of electron-cloud code POSINST
with 3-D accelerator*.
Institute: Lawrence Berkeley National Laboratory
J.-L. Vay1,3, M. A. Furman1, A. W. Azevedo1,3, R. H. Cohen2,3, A. Friedman2,3, D. P. Grote2,3, P. H. Stoltz4, S. A. Veitzer4
1 Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA 2 Lawrence Livermore National Laboratory, Livermore, CA 94550 USA 3 Heavy-Ion Fusion Virtual National Laboratory 4 Tech X Corp., Boulder, CO USA
We have integrated the electron-cloud code POSINST with WARP - a 3-D parallel Particle-In-Cell (PIC) accelerator code developed for Heavy Ion Inertial Fusion (HIF) - so that the two can interoperate. To the combined package, POSINST brings the models related to Electron-Cloud Effect (ECE) studies, a mode of operation (thin slice fixed in the laboratory frame with time as the independent variable) adapted to studies of ECE in high energy accelerators, with specialized preformatted input and output files and related routines. WARP brings 3-D/R-Z time-dependent and X-Y z/s-dependent modes of operations with complicated geometries, MAD-like manipulation of accelerator beam lines, parallelism, advanced diagnostics and interactivity through a Python interpreter (already used in WARP) and a graphical user interface. Both codes are run in the same process, communicate through the Python interpreter, and share certain key arrays (so far, particle positions and velocities). Currently, POSINST provides primary and secondary sources of electrons, beam bunch kicks, a particle mover, and diagnostics. WARP provides the field solvers and diagnostics. Interfaces to the POSINST secondary emission routines are provided by the Tech-X package CMEE . In the future, the codes will be further integrated and WARP’s particle movers will be used, providing access to modules that treat collisions with complicated geometry, as well as several particle motion integrators, including a newly developed drift kinetic hybrid mover . Ultimately, a user will have access to a unique code for 3D and (r,z) thick slice runs or (x,y) and (r) thin slice runs on serial or parallel computers. We will present the status of the development and results of simulations, as available.
* Work performed under the auspices of the U.S Department of Energy by the University of California, Lawrence Livermore and Lawrence Berkeley National Laboratories under contracts No. W-7405-Eng-48 and DE-AC03-76SF00098.  P. Stoltz et. al., this Conference  R. Cohen et. al., this Conference
1, Cyclotron road BLDG 47R0112 Berkeley, Ca 94720, USA
Title: Experimental Studies of Electron Cloud Effects at the Los
Alamos PSR: a Status Report*
R.J. Macek, A.A. Browman, M.J. Borden, D.H. Fitzgerald, R.C. McCrady, T. Spickermannn, and T.J. Zaugg, Los Alamos National Laboratory, USA
Various electron cloud effects (ECE) including the two-stream (e-p) instability at the Los Alamos Proton Storage Ring (PSR) have been studied extensively for the past five years with the goal of understanding the phenomena, mitigating the instability and ultimately increasing beam intensity. The specialized diagnostics used in the study are two types of electron detectors, the retarding field analyzer and the electron sweeping detector, which have been employed to measure characteristics of the electron cloud as functions of time, location in the ring and various influential beam parameters plus a short stripline beam postion monitor to measure high frequency motion of the beam centroid. The main results of this study program will be reviewed and sumarized along with more detail on recent results obtained since the ECLOUD’02 workshop. More recent results include aditional data on effects of beam scrubbing over time, studies of the sources of intial or “seed” electrons, additional studies of electron cloud dissipation after the beam pulse is extracted, studies of the effect of external excitation (a single weak kick) on intense beams in the presence of a significant electron cloud, studies of the “first pulse instability” issue, and more results (mixed) on electron suppression as a cure for the instability. Plans for future work will also be mentioned.
* Work conducted at the Los Alamos National Laboratory, operated by the University of California for the U.S. Department of Energy under Contract No. W-7405-ENG-36.
LANSCE-DO, MS-H812, Los Alamos National Laboratory, Los Alamos, NM 87544, USA
Title: 3-D Parallel Simulation Model of Continuous Beam-Cloud
A new 3D Particle-In-Cell model for continuous modeling of beam and electron cloud interaction in a circular accelerator is presented. A simple model for lattice structure, mainly the Quadrupole and dipole magnets and chromaticity have been added to a plasma PIC code, QuickPIC, used extensively to model plasma wakefield acceleration concept. The code utilizes parallel processing techniques with domain decomposition in both longitudinal and transverse domains to overcome the massive computational costs of continuously modeling the beam-cloud interaction. Through parallel modeling, we have been able to simulate beam propagation through up to 2000 turns of the LHC ring.Emittance and spot size growths have been studied for various circular accelerators and storage rings, (e.g. CERN-SPS, LHC and PEP-II) and the results compared with the previous single-kick models for electron cloud(e.g. HEAD-TAIL). The growth predicted by our code is generally less than that predicted by these models. It is also shown that the single kick approximation may not be accurate for beam- electron cloud modeling due to the highly nonlinear nature of the problem.
3737Wattway Road, PHE Bldg. room #508, Los Angles,CA, 90089
Title: Centroid Theory of Transverse Electron-Proton Instability in a
Long Proton Bunch Revisited: An Erratum
Institute: Los Alamos National Laboratory
Tai-Sen F.Wang, Paul J. Channell, Robert J. Macek /LANL, Ronald C. Davidson/PPPL
In a recent publication on the transverse electron-proton (e-p) instability, an asymptotic solution of the coupled linear centroid equations was derived in the time domain for investigating the e-p instability in long proton bunches with nonuniform line densities. Lately, an error has been found in that work. This erratum discusses in detail the correction and the consequential revisions to the earlier results.
1. T. F.Wang, P. J. Channell, R. J. Macek and R. C. Davidson, “Centroid theory of transverse electron-proton two-stream instability in a long proton bunch,” PRST-AB, 6, 014204 (2003).
MS B259 Los Alamos National Laborqatory Los Alamos, NM 87545 USA
Title: STudy of coupled bunch instability caused by electron cloud
K. Ohmi, KEK
Coupled bunch instability caused by electron cloud has been reported many positron and proton storage rings. The early studies of electron cloud effect were started form understanding the coupled bunch instability. We reviewed the theories and experiments of the instability.
1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
Title: Electron cloud effects in a coasting proton beam
K. Ohmi and T. Toyama, KEK G. Rumolo, GSI
Electrons are accumulated by a coasting beam but are diffused by a small perturbation of the beam. To observe the instability with visible amplitude, the electron production rate should be much higher than that due to ionization. We consider the electron production mecahnism with higher rate. Though electrons from chamber wall are not trapped by the coasting beam, its higher rate may contribute the instability. We study coasting beam instability caused by electrons produced at wall with higher rate.
1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan
Title: Electron cloud effects in JLC damping ring II
K. Ohmi, KEK
Electron cloud instability in JLC damping ring was reported in previoud ECLOUD workshop. We show some new results for the head-tail instability caused by electron cloud. This talk is short one.
1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan
Title: Experimental Results of a LHC Type Cryogenic Vacuum System
Subjected to Electron Cloud
V. Baglin, B. Jenninger CERN, Geneva, Switzerland
The electron cloud is of major concern for most of the storage rings operating with large bunch current and low bunch spacing. The Large Hadron Collider (LHC) operating at cryogenic temperature will have to face the electron cloud. For this reason, the first experimental studies related to the electron cloud in a LHC type cryogenic vacuum system have been launched in 2002 after the closure of the Electron Positron Accumulator (EPA) synchrotron radiation experimental program. The cold bore experiment (COLDEX) has been installed in the CERN Super Proton Synchrotron (SPS) where electron cloud could be produced. Results of the investigations, which include measurements of the dynamic heat deposition, dynamic total pressure rise and residual gas composition as a function of beam operation dose will be presented. Experiments with pre-condensed gas layers of H2, H2O, CO and CO2 onto the beam screen are described. Preliminary results of the beam screen conditioning at 50 K and with 75 ns bunch spacing are presented. Implication to the LHC design and operation are discussed.
AT/VAC 1211 Geneva 23 Switzerland
Title: Summary of Pressure Rise Workshop
Institute: BNL, USA
S.Y. Zhang and T. Roser BNL
The summary of 'Workshop of Beam Induced Pressure Rise in Rings' will include: A brief background of the workshop,results and development on electron and ion desorption, chamber coating and treatment, and electron cloud effect. Perspective of the pressure rise workshop and ECLOUD workshop will also be presented.
911B, BNL, Upton, NY 11973
Title: Design and Implementation of SNS Accumulator Ring Vacuum System
with Suppression of Electron Cloud Instability*
Institute: Brookhaven National Laboratory
H.C. Hseuh for SNS/BNL Team, Brookhaven National Laboratory
BNL is responsible for the design and construction of the 1-GeV accumulator ring for the US Spallation Neutron Source. To minimize the electron cloud instability due to electron multi-pacting in the accumulator ring, the inner surface of the vacuum chamber wall is coated with titanium nitride (TiN) to reduce the secondary electron emission. The striped electrons at the injection stripping foil are guided to the electron collector by the shaped magnetic field and the clearing electrode. Beam-position-monitors may be modified as clearing electrodes. Solenoid is wound at the collimation region to confine the scattered electrons. Additional pumping ports are reserved for future vacuum upgrade and for beam scrubbing with turbopumps. The design and implementation of all these measures will be presented with emphasis on TiN coating and secondary electron yields.
*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.
Collider-Accelerator Department Building 911B, BNL Upton, NY 11973-5000
Title: Simulation of the Electron Cloud Effects for the SNS Ring
Institute: Indiana University, Bloomington; SNS project, ORNL
email: email@example.com, firstname.lastname@example.org
Y. Sato (Indiana University), J. Holmes, S. Danilov, A. Shishlo, S. Henderson, SNS project, ORNL
During the past year, we have developed an electron cloud module and implemented it into the ORBIT Code for beam dynamics in high intensity rings. In addition to studying the dynamics of the electron cloud, our intent in developing this model is to examine the effect of the electron cloud on the protons. In this presentation, we examine benchmarking and initial applications of the ORBIT electron cloud module to SNS. In addition to considering the development of the electron cloud, We discuss its interaction with and effect on the proton beam. All these dynamics will be shown for different magnetic field configurations and for a number of beam pipe materials.
Research sponsored by UT-Batelle, LLC, under contract no. DE-AC05-00OR22725 and DE-FG02-92ER40747 for the U.S. Department of Energy, and NSF under contract no. PHY-0244793. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos and Oak Ridge.
Accelerator Systems Division, SNS project, 701 Scarboro Road, Oak Ridge, Tennessee 37830
Title: Electron-Cloud Module for the ORBIT Code
Institute: SNS project, ORNL
A.Shishlo, Y. Sato, J. Holmes, S. Danilov, S. Henderson, SNS project, ORNL
During the past year, we have developed an electron cloud module and implemented it into the ORBIT Code for beam dynamics in high intensity rings. In addition to studying the dynamics of the electron cloud, our intent in developing this model is to examine the effect of the electron cloud on the protons. This new model includes full 3D descriptions of the proton bunch and the electron cloud, including their space charge interactions as well as their motion in external electric and magnetic fields. Primary electrons are created by beam ionization of neutral gas and interaction with the beam pipe walls, while secondary emission of electrons is calculated using a set of models based on that of M. Furman and M. Pivi. The ORBIT electron cloud model simulates the electron cloud (EC) development including interactions with and effect on the proton bunch in a selected segment of the ring. The electron cloud module has been fully integrated into the ORBIT code environment. The structure, algorithms, parallel implementation, and benchmarks with analytic results will be presented. Research sponsored by UT-Batelle, LLC, under contract no. DE-AC05-00OR22725 and DE-FG02-92ER40747 for the U.S. Department of Energy, and NSF under contract no. PHY-0244793. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos and Oak Ridge.
Accelerator Systems Division, SNS 701 Scarboro Road Oak Ridge, TN 37830
Title: Instrumental Effects in Secondary Electron Yield and
Energy Distribution Measurements
Institute: Stanford Linear Acclerator Center
Robert E. Kirby, Stanford Linear Accelerator Center, Stanford University, 2575 Sand Hill Rd, Menlo Park, CA 94025
Measurement of electron yields and electron energy distributions appears straightforward - simple equipment, simple electronics, easy-to-acquire data, at least in a laboratory setting. Unfortunately, the low secondary electron energy (2-5 eV) and the extreme sensitivity of the yield to surface condition and surrounding environment make the measurement details anything but simple. These problems affect the accuracy and interpretation of the experimental results, often in a subtle way. Most troublesome is the production of unwanted (and unexpected) secondary electrons from within the electron sources and detectors, and from the surrounding vacuum chamber. In addition, the sample surface condition can change during measurement, for example, through electron damage or enhanced oxidation/carburization. Electron source, analyzer, and sample effects will be discussed with examples for copper, TiVZr non-evaporable getter, niobium and TiN on various substrates.
MS 74, 2575 Sand Hill Rd, Menlo Park, CA94025
Title: Vacuum and electron cloud issues at the GSI present and future
G. Rumolo, O. Boine-Frankenheim, E. Mustafin, I. Hofmann/GSI
According to the international accelerator project at GSI, the double synchrotron SIS100/300 and a chain of storage rings will be built (using the present GSI synchrotron SIS18 as injector) in order to achieve high intensity and high energy heavy ion pulses for nuclear or plasma physics studies or anti-proton production. Dynamic vacuum instability and electron cloud are potential intensity limiting factors in the SIS18 and SIS100/300, which need to be investigated. Dynamic vacuum instability induced by ion loss due to charge exchange presently limits the intensity in the SIS18 to a few 10^9 U+28, well below the design goal value needed for the future facility. NEG-coating of the vacuum chamber surface and a system of collimators to intercept the beam losses in a controlled way are the measures presently under study to push up the instability threshold. A broad simulation campaign aimed at defining possible electron cloud issues in the SIS18 and in the SIS100/300 shows on the other hand that the thresholds for electron cloud build up in terms of SEY are rather high. Parameters like SEY and dimensions of the beam vacuum chamber for SIS100/300 have been swept over wide ranges of values, and good sets for the safe ring operation are thus identified.
Planckstrasse, 1 D-64291 Darmstadt (Germany)
Title: Electron cloud and Vacuum effects in the SPS
First_Name: Jose Miguel
J.M. JIMENEZ / CERN - Geneva Switzerland
The 2004 SPS run with LHC-type beams will probably be the latest one before the start up of the LHC machine and a number of opened questions still remain. During this presentation, the behavior of the SPS as the future injector of the LHC will be reviewed and the opened questions will be discussed. The experimental program which has been prepared will be presented and discussed together with new detectors being installed in the SPS ring. This experimental program aims to confirm the preliminary results on the heat loads, vacuum cleaning and beam conditioning under both dipole and field free conditions at RT and at 4.5 or 30 K and provide information on the parameters which could play a non negligible role in the extrapolation of the SPS results towards the LHC.
1211 Geneva 23 Switzerland
Title: Electron cloud effects in the J-PARC rings and related topics
Takeshi Toyama, K. Ohmi, M. Tomizawa, KEK
Tentative design relating to electron clouds in the J-PARC rings will be presented. Some experimental results will be also reported. Using an electron-sweeping detector of the same type as the LANL-LANSCE (R. Macek et al.), we obtain swept electron signals in the KEK-PS main ring. Comparison with simulation results will be discussed.
Oho 1-1, Tsukuba, Ibaraki 305-0801, Japan
Title: SEY and electron cloud build-up with NEG materials
Rossi Adriana/ CERN
The LHC room temperature sections will be coated with Non Evaporable Getter (NEG) materials for, among others, their properties of antimultipactor. Laboratory measurements of Secondary Electron Yields (SEY) of TiZrV NEG coatings have shown that after 2h heat treatment at 160 and 200°C, the maximum SEY decreases from 2 to below 1.4 and 1.1 respectively. Saturation with H2, H2O, CO and CO2 at low pressure increases the SEY by about 0.1. This outcome is supported by the results on a NEG coated chamber in the SPS accelerator ring, with LHC type proton beam. The untreated NEG surface multipacts as any unbaked surface, while no electron cloud build-up was observed after 4h heat treatment at 250°C and subsequent saturation with mainly water vapour. We give here a review of SEY on NEG surfaces and present the results of electron cloud build-up measurements with NEG coated vacuum chambers.
1211 Geneva 23 Switzerland
Title: Multipacting and remedies of electron cloud in long bunch
LANFA WANG, BNL/SNS Team
The mechanism of electron multipacting in long bunched proton machine has been quantitatively described by the electron energy gain and electron motion. Some important parameters related to electron multipacting are investigated in detail. It is proved that multipacting is sensitive to beam intensity, longitudinal beam profile shape and transverse beam size. Agreements are achieved among our analysis, simulation and experiment. We also describe the remedies to remove the electron cloud in long bunch machine.
Building 817, Brookhaven National Lab, Upton, NY, 11973
Title: Electron Cloud Build-Up Simulations with ECLOUD
Daniel Schulte, CERN
The talk will give an overview of the status of electron cloud build-up simulations at CERN, using the ECLOUD code. The recent code modifications will be mentioned and comparisons of simulation results with measurements in the SPS will be discussed.
Title: Extending Possibilities of Analyzing the Electron Cloud Effect
on Beam Stability
Institute: Budker Institute of Nuclear Physics
E. Perevedentsev, Budker Institute of Nuclear Physics, Novosibirsk 630090 Russia
Conventional formalism for the coherent beam stability evaluation can be modified so as to account for the cloud-specific differences from the standard description of the beam-environment interaction. Extension of the wake-and-impedance approach aimed at applying to the two-stream problems is presented. It may prove useful for both analytical work and simulation.
11, Lavretiev Ave., Novosibirsk 630090 Russia
Title: Electron Cloud Observations: A Retrospective
Institute: Argonne National Laboratory
Katherine Harkay, Argonne National Laboratory
Study of electron clouds in high intensity storage rings remains a important area of R&D 30 years after the first observations were made. The list of cloud-induced effects continues to grow as new observations are reported. Data from dedicated electron cloud diagnostics, used in combination with standard beam diagnostics, have contributed to a better understanding of the physics of the electron cloud and its interaction with the beam. In this talk, examples of electron cloud observations have been selected from the published record to highlight various important aspects of the physics. Comparisons of data among various rings show interesting similarities and differences. Such data, used in combination with modeling and analytical calcultions, more fully characterize the electron cloud distribution and help to identify cures. Rather than attempt to be comprehensive, this talk is meant to illustrate what we have learned and what needs to better understood.
ASD/401 9700 S. Cass Ave. Argonne, IL 60439
Title: Effect of the beam instability on e-cloud density //
Secondary yield in the presence of the beam
Institute: SLAC, Stanford University
Sam Heifets, SLAC
Some simulations of the e-cloud the equilibrium density of the cloud is pre-calculated and then used in the study of beam stability. Actually, the density of the electron cloud is a dynamic variable which has to be defined in simulations self-consistently. As example of a similar problem of the beam-ion interaction is given. The second part of the talk considers effect of the fields of the beam and ions on the yield of the secondary emission and shows that yield can be affected by ions.
Stanford Linear Accelerator Center, PO Box 20450, Stanford, CA 94309-2010
Title: Interplay of electron cloud and machine impedance
K. Cornelis, CERN
In the SPS the electron cloud is mainly produced in the dipoles. This leads to specific beam instabilities which are quite different in horizontal and vertical plane. The influence geometry of, both the wake field and the electron cloud, are discussed.
CH-1211 GENEVA, SWITZERLAND