CMAD: A Self-consistent Parallel Code to Simulate the Electron Cloud Build-up and Instabilities

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 resolves the interaction between the beam and the cloud at each element location, with different cloud distributions at each magnet location. The goal of CMAD is to simulate single- and coupled-bunch instability, allowing tune shift, dynamic aperture and frequency map analysis and the determination of the secondary electron yield instability threshold. The code is in its phase of development and benchmarking with existing codes. Preliminary results on benchmarking are presented in this paper

Modeling of E-Cloud Build-Up in Grooved Vacuum Chambers using POSINST

Use of grooved vacuum chambers have been suggested as a way to limit electron cloud accumulation in the ILCDR. We report on simulations carried out using an augmented version of POSINST, accounting for e-cloud dynamics in the presence of grooves, and make contact with previous estimates of an effective secondary electron yield for grooved surfaces

Sharp Reduction of the Secondary Electron Emission Yield from Grooved Surfaces

The effect of an artificially-enhanced rough surface on the secondary electron emission yield (SEY) was investigated both theoretically and experimentally. Analytical studies on triangular and rectangular grooved surfaces show the connection between the characteristic parameters of a given geometry to the SEY reduction. The effect of a strong magnetic field is also discussed. SEY of grooved samples have been measured and the results agree with Monte-Carlo simulations

Microwave Transmission Measurements of the Electron Cloud Density In The Positron Ring of PEP-II

Clouds of electrons in the vacuum chambers of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electron clouds over substantial lengths of the beam pipe. We applied a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a straight section of the accelerator. The modulation in the wave transmission which appear to increase in depth when the clearing solenoids are switched off, seem to be directly correlated to the electron cloud density in the section. Furthermore, we expect a larger phase shift of a wave transmitted through magnetic dipole field regions if the transmitted wave couples with the gyration motion of the electrons. We have used this technique to measure the average electron cloud density (ECD) specifically for the first time in magnetic field regions of a new 4-dipole chicane in the positron ring of the PEP-II collider at SLAC. In this paper we present and discuss the measurements taken in the Low Energy Ring (LER) between 2006 and 2008

Observation of Magnetic Resonances in Electron Clouds in a Positron Storage Ring

The first experimental observation of magnetic resonances in electron clouds is reported. The resonance was observed as a modulation in cloud intensity for uncoated as well as TiN-coated aluminum surfaces in the positron storage ring of the PEP-II collider at SLAC. Electron clouds frequently arise in accelerators of positively charged particles, and severely impact the machines performance. The TiN coating was found to be an effective remedy, reducing the cloud intensity by three orders of magnitude

A New Chicane Experiment in PEP-II to Test Mitigations of the Electron Cloud Effect for Linear Colliders

Beam instability caused by the electron cloud has been observed in positron and proton storage rings, and it is expected to be a limiting factor in the performance of future colliders [1-3]. The effect is expected to be particularly severe in magnetic field regions. To test possible mitigation methods in magnetic fields, we have installed a new 4-dipole chicane experiment in the PEP-II Low Energy Ring (LER) at SLAC with both bare and TiN-coated aluminum chambers. In particular, we have observed a large variation of the electron flux at the chamber wall as a function of the chicane dipole field. We infer this is a new high order resonance effect where the energy gained by the electrons in the positron beam depends on the phase of the electron cyclotron motion with respect to the bunch crossing, leading to a modulation of the secondary electron production. Presumably the cloud density is modulated as well and this resonance effect could be used to reduce its magnitude in future colliders. We present the experimental results obtained during January 2008 until the April final shut-down of the PEP-II machine

Science Requirements and Conceptual Design for a Polarized Medium Energy Electron-Ion Collider at Jefferson Lab

This report presents a brief summary of the science opportunities and program of a polarized medium energy electron-ion collider at Jefferson Lab and a comprehensive description of the conceptual design of such a collider based on the CEBAF electron accelerator facility.Comment: 160 pages, ~93 figures This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC05-06OR23177, DE-AC02-06CH11357, DE-AC05-060R23177, and DESC0005823. The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purpose

Active Damping of the E-P Instability at the Los Alamos Proton Storage Ring

A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). The feedback system configuration, setup procedures, and optimization of performance are described. Results of several experimental tests of system performance are presented including observations of instability threshold improvement and grow-damp experiments, which yield estimates of instability growth and damping rates. A major effort was undertaken to identify and study several factors limiting system performance. Evidence obtained from these tests suggests that performance of the prototype was limited by higher instability growth rates arising from beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback

Modeling incoherent electron cloud effects

Incoherent electron effects could seriously limit the beam lifetime in proton or ion storage rings, such as LHC, SPS, or RHIC, or blow up the vertical emittance of positron beams, e.g., at the B factories or in linear-collider damping rings. Different approaches to modeling these effects each have their own merits and drawbacks. We describe several simulation codes which simplify the descriptions of the beam-electron interaction and of the accelerator structure in various different ways, and present results for a toy model of the SPS. In addition, we present evidence that for positron beams the interplay of incoherent electron-cloud effects and synchrotron radiation can lead to a significant increase in vertical equilibrium emittance. The magnitude of a few incoherent e+e- scattering processes is also estimated. Options for future code development are reviewed

Accelerator Physics Code Web Repository

In the framework of the CARE HHH European Network, we have developed a web-based dynamic acceleratorphysics code repository. We describe the design, structure and contents of this repository, illustrate its usage, and discuss our future plans, with emphasis on code benchmarking