Longitudinal and transverse dynamics of ions from residual gas in an electron accelerator

Abstract

The ion cloud produced from residual gas in an electron accelerator can degrade machine performances and produce instabilities. The ion dynamics in an accelerator is governed by the beam-ion interaction, magnetic fields and eventual mitigation strategies. Due to the fact that the beam has a nonuniform transverse size along its orbit, the ions move longitudinally and accumulate naturally at some points in the accelerator. In order to design effective mitigation strategies it is necessary to understand the ion dynamics not only in the transverse plane but also in the longitudinal direction. After introducing the physics behind the beam-ion interaction, we show how to get accumulation points for a realistic electron storage ring lattice. Simulations of the ion cloud dynamics, including the effect of magnetic fields on the ions, clearing electrodes and clearing gaps are shown. Longitudinal ion trapping due to the magnetic mirror effect in the dipole fringe fields is also detailed. Finally, the effectiveness of clearing electrode using longitudinal clearing fields is discussed and compared to clearing electrodes producing transverse field only.

Longitudinal impedance and coherent synchrotron radiation models for ThomX storage ring

“…In ThomX, some BPMs have double BPM blocs with six or hight electrodes. The additional buttons are used as ion clearing electrodes to avoid ion trapping by the electron beam [8,19]. In a button BPM, the electromagnetic fields excited by the beam can be trapped in the structure.…”

Research on the deposition and properties characterization of novel conductive getter films on the inner wall of accelerator vacuum chamber

“…The flow conductance limitation caused by the small aperture vacuum chamber makes the traditional lumped-pump pumping set-up unable to meet the requirements of the HALF storage ring beam operation in the vacuum environment [2].As for the NEG film deposited on the vacuum chamber wall by magnetron sputtering coating method, not only can the evaporable rate of the substrate be reduced [3][4][5][6], but also after baking and activation, the getter material can effectively adsorb O 2 , CO, CO 2 , H 2 and other gases through chemical reaction with active gases. The wall of the vacuum chamber is changed from a outgassing source to a sorbing surface [7][8][9][10]. In addition, the activated NEG film also has a lower photon stimulated desorption (PSD) yield and electron stimulated desorption (ESD) yield [11][12][13].…”

Investigation on the Ion Motion towards Clearing Electrodes in High-Brightness Electron Accelerators

“…Often in modern facilities, not just a single electrode, i.e. a biased stripe or button, but an electrode configuration consisting of several charged stripes or buttons positioned around the beam pipe at a given location is used to enable ion-clearing, see for example [3,4]. Please note that such a configuration of clearing electrodes is simply referred to as clearing electrode in this paper.…”