저장링에서 전자구름에 의한 양전자 빔의 불안정성

Abstract

The effects of electron cloud on the motion of the circulating ultra low emittance positron beam are studied in this thesis. Specifically, the study focuses on elec-tron cloud’s effect in Cornell Electron Storage Ring Test Accelerator (Cesr-TA) and the International Linear Collider (ILC) damping ring by linearized theory and simulation tools. Cesr-TA has been operating to experiment for the ILCdamping ring with different positron beam energies: 2 and 5 GeV. The elec-tron phase factor, !e y z=c, is given differently to each case. The single-bunch instability is investigated with analytic prediction and simulations based on the weak-strong and strong-strong models by using the simplified lattice. The simulation results are favorably compared with analytical predictions. The threshold densities of electron cloud for the fast head-tail instability obtained by weak-strong and strong-strong simulations agree with the predicted values by linear theory. The betatron tune shift caused by electron cloud is also investigated with two simulation methods, the results coincide with predicted values. By using the strong-strong simulation model, we investigate the effects of the bunch-by-bunch feedback of about 50 turns, non-zero dispersion, and bending magnetic field. The simulation results show that the feedback system suppresses the dipole motion and increases the threshold density in 2 GeV case, but is less effective in 5 GeV case. The threshold densities are degraded with non-zero dispersion in both cases, but the rates of degradation appear differently. By the effect of bending magnetic field, the threshold density is increased because the cloud density is reduced at the beam center. We discuss an incoherent emittance growth using the realistic lattice model for Cesr-TA. Below the threshold, the incoherent emittance growth may not be serious in Cesr-TA and the ILC damping ring. The threshold density is obtained using OCS6 lattice in ILC damping ring. The results of simulations agree with the predicted value inILC dampig ring.