Laser wakefield accelerators and laser instabilities in a hollow plasma channel.

摘要

The plasma-based accelerators have several attractive features such as high accelerating gradient, potentially high beam qualities, etc. In this dissertation we investigate these properties in a hollow plasma accelerator. The issues include the normal mode solutions of plasma wave and laser wave, the laser instabilities, and the beam dynamics. A 2-1/2 dimensional Particle-In-Cell (PIC) computer program (ISIS) is modified to simulate the hollow channel geometry. The simulation results are shown to agree with the theories.; For the study of laser instabilities, we focus on the Raman forward scattering (RFS) and laser hose instability of the laser pulses. Because the channel can support both body mode (mode at plasma frequency) and surface mode (mode at channel frequency), the laser pulse can couple energy to both modes and exhibits a unique dispersion relation for the RFS. The temporal growth rates of 3-wave and 4-wave processes are derived and used to estimate the amplitude of the decayed waves. The laser hose instabilities are studied through PIC simulations for various plasma geometries. It is found that in hollow channel plasma, both RFS and laser hose instability can be either largely suppressed or completely avoided.; The dynamics of the particles inside the channel are relatively simple and easy to control because of the unique wakefield structure. The absence of transverse forces inside of a hollow channel enables the acceleration of beams with extremely low emittance. The plasma/vacuum boundaries can form a potential barrier which prevents the particles from escaping from the channel. The study of longitudinal dynamics reveals a strategy for phasing and beam loading to minimize the energy spread of accelerated beams while at the same time achieving high energy extraction efficiency. PIC simulations show that high overall efficiency (e.g., 25% from driving source to accelerated beam), low emittance {dollar}(epsilonsb{lcub}n{rcub} < 0.25mm - mrad){dollar} and small energy spread {dollar}(deltagamma/Deltagamma sbsp{lcub}sim{rcub}{lcub}<{rcub} 3%){dollar} can be achieved simultaneously in hollow plasma accelerators.