The Study Of The Residual Gas Scattering In The Electron Storage Ring

Vacuum system is an important part of the accelerator. The interactions between residual gas and electron beam can reduce the beam quality. This effect may be even more serious in the storage ring because the cyclotron motions of the electrons, so the beam lifetime in storage ring is mainly decided by the vacuum conditions. Besides, the residual gas scattering can change the distribution of the beam, and increase the emittance.The early research on the residual gas scattering only gave some theoretical derivation and formula about the beam lifetime related to this effect. In the recent years, there’s a few or individual research has started to use MCC simulation to calculate the beam lifetime. But after an overview of this research area, we find there is no concrete analysis of the change of beam distribution and emittance caused by the residual gas scattering.In this paper, we use PIC-MCC methods to simulate the effect of the residual gas scattering in the electron storage ring. And we take the Hefei Advanced Light Source (HALS) as simulation object. HALS is a diffraction limit storage ring designed by the National Synchrotron Radiation Laboratory (NSRL). The emittance of HALS can reach dozens of pmrad, in this circumstances the residual gas scttering will do a greater impact on the electron beam.To see the change of the beam distribution and emittance caused by residual gas scattering, we can not only consider the scattering causing the loss of particles, like former research. In this paper, we use a proper scattering cross section and scattering angle sampling method, so the scattering in all angles are discussed in our simulation.Besides, the former research and simulation about the residual gas coulomb scattering only gave a’kicker’on the deflection angle of the collided electrons. In this paper, we derived the formula of coulomb scattering collision between electrons and residual gas molecule in storage ring. The formula is used to calculate the electron momentum after collision, which restore the real process of the electron beam scattering caused by residual gas.The results shows that the simulated beam lifetime is very close to the theoretical value, and there is a tail in the horizontal beam distribution caused by the residual gas scattering. It also shows that the residual gas scattering can cause the increase of the beam emittance. Finally, by analyzing the positions of the scattering electrons, the contributions of the scattering electrons do to the lifetime, to the distribution and the emittance are discussed.Investigation of this subject is supported by National Natural Science Foundation project11175182and11175180.