Numerical Investigation Of Dielectric Grating Accelerators

Particle accelerators are ubiquitous in modern research,industrial,and medical facilities,but they are often large,prohibitively expensive,and have limited accessibility.This size and expense is due in large part to the low accelerating gradients achievable in radio frequency accelerators,limited by high-field breakdown to?30 Me V/m.Leveraging nano fabrication techniques developed by the electronics industry and ultrafast laser technology,Dielectric Laser Accelerators(DLAs)have the potential to provide one to two orders of magnitude higher accelerating gradients than radio frequency accelerators,allowing compact and accessible accelerators to be produced.This thesis describes the numerical optimization of dielectric grating based particle accelerators which can be powered by laser and terahertz light sources.First,we introduced an optimized grating structure for non-relativistic electron acceleration.We present the theory behind grating-based particle acceleration and discuss simulation results.Our simulation results show that the previously proposed dielectric grating structure has deceleration regions along the whole acceleration process which are unfavorable for achieving high gradient.We proposed a so called asymmetric grating structure which is required two side pumping with proper phase difference of driving laser pulses.This structure has a potential in non-relativistic electron bunch acceleration,and the expected acceleration gradient is up to?430Me V/m.Then we introduced a grating structure to relativistic particle acceleration which is designed for terahertz pulse operation.Dielectric laser accelerators are facing a tough problem in beam loading.Using THz pulses to generate an accelerating field in a dielectric loaded accelerator structure is a promising way to mitigate the disadvantages of RF and Laser accelerator structures.We numerically investigated a single side coupling THz driven dual-grating structure which is composed of Silicon Dioxide(Si O₂),the average acceleration gradient for relativistic electrons is up to?350 Me V/m.This thesis also proposed an energy efficient side-coupling dielectric single grating structure accompanied with a multi-layer Bragg reflector.Simulation results show that the reflector structure effectively manipulates the THz field compared to dual-grating structure,not only boosts the field strength in the accelerating channel,but also optimizes the field distribution and generates a periodic field reversal to achieve better phase synchronicity for relativistic particles,thereby increasing the accelerating gradient by more than 40%.It was also found that the energy-recycling capability of a Bragg-reflector highly depends on the operating THz pulse duration and beam channel width.Choosing longer pulse duration and setting a narrower beam channel width with optimum pillar height can increase the single pulse efficiency more than 70%compared to the bare dual-grating structure.Our results set the stage for the development of future multi-staged DLA devices composed of integrated on-chip systems.