Space charge and electron clouds issues

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2000

An electron cooling system has started operation in the heavy ion synchrotron SIS which is used to increase the intensity for highly charged ions. Fast transverse cooling of the hot ion beam after horizontal multiturn injection allows beam accumulation at the injection energy. After optimization of the accumulation process an intensity increase in a synchrotron pulse by more than one order of magnitude has been achieved. For highly charged ions the maximum number of particles has been increased from 1;10 to 1;10. For lighter ions intensity limitations have been encountered which are caused by the high phase space density of the cooled ion beam. Momentum spreads in the 10\ range and emittances well below 10 mm mrad have been demonstrated. Recombination losses both in the residual gas and with the free cooler electrons determine the maximum intensity for highly charged ions. Systematic measurements of the recombination rates have been performed providing data for an optimum choice of the charge state. Strong enhancement of the recombination rate with free electrons compared to theoretical calculations of radiative electron capture have been observed.

2010

The containment of beams in the longitudinal direction is fundamental to the operation of accelerators that circulate high intensity beams for long distances such as the University of Maryland Electron Ring (UMER); a scaled accelerator using low-energy electrons to model space-charge dynamics. The longitudinal space-charge forces in the beam, responsible for the expansion of the beam ends, cause a change in energy at the beam head/tail with respect to the main injected energy or flat-top part of the beam. This paper presents the first experimental results on using an induction cell to longitudinally focus the circulating beam within the UMER lattice for multiple turns.

2003

, high bunch intensities LHC-type beams were injected for the first time in the SPS inducing strong vacuum pressure rises, perturbations on the electrostatic pickups and beam instabilities. Evidences of the electron cloud phenomenon as the mechanism responsible for these instabilities are reviewed. This paper also presents the results obtained with several detectors installed in the SPS machine to improve the understanding of the electron cloud mechanism and refine the simulations. The spatial distributions of the electrons in the cloud are shown in presence of and without a dipole magnetic field. The effects of the beam intensity and filling pattern on the behaviour of the electron cloud are presented. The scrubbing effect is studied using an in-situ measurement of the secondary electron yields. Finally, the potential limitations due to the electron cloud in the SPS and the issues for the LHC are discussed. Possible remedies will be presented, i.e. nitrogen and argon glow discharges or new filling schemes. AB, AT Divisions Presented at the "Mini-Workshop on SPS Scrubbing Run Results and Implications for the LHC"

Electron-cloud effects presently limit the performance of several accelerators operating with high beam current, notably the SLAC and KEK B factories, the CERN SPS, the CERN PS, and the Los Alamos PSR. They are a major concern for many future projects, e.g., the CERN LHC and the SNS. An electron cloud is generated in the vacuum chamber by photoemission or beam-induced multipacting and subsequent electron accumulation during a bunch or bunch-train passage. Both coupled and single bunch instabilities, pressure rise, malfunctioning of beam diagnostics and failures of multi-bunch feedback systems have all been attributed to the cloud electrons. We compare observations from various laboratories with computer simulations and analytical estimates, and we address mechanisms by which the electrons may dilute the beam emittance. Possible cures and future research directions are also discussed.

2005

In the FAIR [1] facility planned at GSI high space charge may play an important role for limiting the foreseen nominal machine performance. In the SIS100, bunches with tuneshift as large as ≈ 0.2 should be stored for hundred thousand turns keeping the loss budget within few percent to avoid quenching of superconducting magnets and vacuum degradation. Usually, design criteria to meet these beam dynamics constraints rely on quantities such as dynamic aperture or nonlinear acceptance. The presence of space charge in a nonlinear lattice sets, however, new challenges to beam loss control and requires an effort to understand unexplored leading beam loss mechanisms. In this context beam loss studies for a high intensity bunched beam have been performed at the CERN-Proton Synchrotron. We discuss the experimental results and propose a mechanism for explaining the observed beam loss. We then apply to the SIS100 what we have learnt from CERN-Proton Synchrotron measurements and discuss its consequences.

2008

The purpose of this course is to provide a comprehensive introduction to the physics of beams with intense space charge. This course is suitable for graduate students and researchers interested in accelerator systems that require sufficient high intensity where mutual particle interactions in the beam can no longer be neglected. Prerequisites: undergraduate level Electricity and Magnetism and Classical Mechanics. Some familiarity with plasma physics, special relativity, and basic accelerator physics is recommended but not required. Objectives This course is intended to give the student a broad overview of the dynamics of beams with strong space charge. The emphasis is on theoretical and analytical methods of describing the acceleration and transport of beams. Some aspects of numerical and experimental methods will also be covered. Students will become familiar with standard methods employed to understand the transverse and longitudinal evolution of beams with strong space charge. The material covered will provide a foundation to design practical architectures. Instructional Method Lectures will be given during morning sessions, followed by afternoon discussion sessions, which will engage the student on the material covered in lecture. Daily problem sets will be assigned that will be 2 of 2 06/06/2008 09:56 PM waste transmutation, etc. Reading Requirements Extensive class notes will be provided that will serve as the primary reference.

An electron cooling system has been designed for the heavy ion synchrotron SIS. The purpose of this device is accumulation of weak injected beams of highly charged ions to the maximum intensity determined by the space charge limit. This is accomplished by repeated multiturn injection and simultaneous cooling at the injection energy. The cooling time has been estimated to be an order of mag- nitude shorter than the acceleration cycle time. Thus a corresponding increase of the average output intensity by about one order of magnitude is expected. The beam qual- ity of the accumulated beams will also be improved. . The ions are injected by multiturn injection into the heavy ion syn- chrotron SIS filling the horizontal acceptance at a fixed en- ergy of 11.4 MeV/u with beams of highly charged ions from the UNILAC accelerator. For the heaviest ion species the intensity of the injected beams is at present more than two orders of magnitude below the values required to fill the SIS up to the ...

2020

Recent technological advances in energy recovery linear accelerators (ERLs) have enabled us to access high energy and high brightness electron beam, allowing us to gain tremendous insights into fundamental physics while also envisioning diverse and robust applications for electron beams. ERLs are recirculating linacs that generate high quality electron beams, with these beams, energy is gained via multiple passes through a superconducting accelerating cavity. After the fully accelerated beam completes its interaction, for example, with an internal target, the electrons are decelerated in the linac, transferring their energy back to the cavity radio-frequency (RF) fields. However, as the beam brightness is increased, collective effects such as space charge considerably affect the beam quality. Space charge modifies the electron beam dynamics in dispersive regions along the beamline. Further, longitudinal space charge together with dispersion can lead to the amplification of the initi...

Physical Review Special Topics - Accelerators and Beams, 2001

Photoemission and secondary emission are known to give rise to a quasistationary electron cloud inside the beam pipe through a beam-induced multipacting process. We investigate the electron-cloud build up and related effects via computer simulation. In our model, macroparticles representing photoelectrons are emitted synchronously with the passing proton or positron bunch and are subsequently accelerated in the field of the beam. As they hit the beam pipe, new macroelectrons are generated, whose charges are determined by the energy of the incoming particles and by the secondary emission yield of the beam pipe. A quasistationary state of the electron cloud is eventually reached due to space charge. The equilibrium density is used as an input parameter for a second program that analyzes the electron-cloud driven single-bunch instability. The electron cloud simulation also allows the evaluation of the heat load on the cold Large Hadron Collider beam screen, which must stay within the available cooling capacity, and the electron charge deposited on or emitted from the electrodes of the beam-position monitors.