Beam Induced Electron Multipacting in the CERN Large Hadron Collider Accelerator LHC

Electron multiplication driven by the electric field of the proton bunches is expected to occur in the Large Hadron Collider (LHC), according to previous studies performed at CERN with two computer simulation codes. Electrons, secondary electrons and photo-electrons created by the beam will be accelerated in the electric field of the proton beam and will produce a large heat load at the surface, space charge in the chamber, coupling between the electrons and the beam and a pressure increase, which ultimately could cause the loss of the proton beam. It is, therefore, fundamental to study the phenomenon. The Ph.D. thesis work included studies and planning for the laboratory experimental setup to reproduce the electron multipacting induced by radio frequency, performing data aquisitionand analysis, modelization and simulations of the phenomenon, furthermore, to study the parameters influencing the effect, such as vacuum chamber material, cleaning, surface treatments, to better understand multipacting and determine the most effective ways to avoid this critical effect for the LHC accelerator

Electron Cloud Updated Simulation Results for the PSR, and Recent Results for the SNS

Recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos are presented in this paper. A refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has recently been included in the electron-cloud code

An Accurate Model of Beam Ion Instability with Nonlinear Space Charge, Realistic Beam Optics and Multiple Gas Species Vacuum Abstract

The previous analyses of beam ion instability have been performed for single gas species only. However, there are multiple gas species in the vacuum chambers of an accelerator. The superposition rule doesn’t apply in general and it overestimates the instability. Therefore, it is important to use multiple gas species model. On the other hand, the variation of beam size along the accelerator ring or linac provides Landau damping to the instability. In previous studies, the effect of beam optics has been represented by a frequency spread and a quality factor. In practice, it could be difficult to accurately estimate the frequency spread and quality factor for general beam optics because the variation of the beam size along the ring usually doesn’t have simple distribution. This paper provides a more accurate method to analyze beam ion instability with arbitrary vacuum component and arbitrary beam optics where the variation of the beam size along the accelerator ring or linac can be arbitrary. Meanwhile, the nonlinear space charge effect is also included and the general beam filling pattern can be easily modeled. Our analyses agree well with expensive simulations. PACS numbers: 29.27.Bd, 29.20.db I

Simulations of Electron Cloud Build Up and Saturation in the APS

In studies with positron beams in the Advanced Photon Source, a dramatic amplification was observed in the electron cloud for certain bunch current and bunch spacings. In modeling presented previously, we found qualitative agreement with the observed beam-induced multipacting condition, provided reasonable values were chosen for the secondary electron yield parameters, including the energy distribution. In this paper, we model and discuss the build-up and saturation process observed over long bunch trains at the resonance condition. Understanding this saturation mechanism in more detail may have implications for predicting electron cloud amplification, multipacting, and instabilities in future rings

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

Beam tube vacuum in a Very Large Hadron Collider; Stage 1 VLHC

Synchrotron radiation induced photodesorption in particle accelerators may lead to pressure rise and to beam-gas scattering losses, finally affecting the beam lifetime. We discuss the beam tube vacuum in the low field Stage 1 Very Large Hadron Collider VLHC. Since VLHC Stage 1 has a room temperature beam tube, a non-evaporable getter (NEG St101 strip) pumping system located inside a pumping antechamber, supplemented by lumped ion pumps for pumping methane is considered. A possible beam conditioning scenario is presented for reaching design intensity. The most important results are summarized in this paper. More detailed reports of the calculations will be presented at the PAC2001 Conference, Chicago, IL to be held in June 2001, and at the Snowmass Conference, CO, to be held on July 2001

Simulation results for the electron-cloud at the PSR

We present a first set of computer simulations for the main features of the electron cloud at the Proton Storage Ring (PSR), particularly its energy spectrum. We compare our results with recent measurements, which have been obtained by means of dedicated probes

Electron-cloud simulation results for the PSR and SNS

We present recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos. In particular, a complete refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has been included in the simulation code