Advanced simulation models and concepts for positron and electron acceleration in plasma wakefield accelerators

Plasma-based wakefield accelerator (PWFA) is an attractive approach for realizing future electron/positron (e-/e+) linear colliders because plasmas can support acceleration gradients 1,000 times larger than conventional accelerators do. The E167 PWFA experiments at SLAC demonstrated an energy gain of 42 GeV after a 85 cm long Li plasma with an implied acceleration gradient of 52 GeV/m. This verifies that such large acceleration gradients are obtainable. The experimental results also showed that a large number of He plasma electrons were trapped in the plasma wake near the heat-pipe oven entrance and then accelerated to multi-GeV energies. In this dissertation, several conceptual and computational advances are presented aimed at understanding the experimental results and furthermore supporting the design of next generation PWFA. This includes the development of high fidelity algorithms, multiple time scale algorithms and a new concept for injecting and accelerating positrons in plasma wakes.;To enhance simulation realism, synchrotron radiation and beam waist location modules are implemented in OSIRIS. Then the high performance one-to-one modeling of E167 experiments using this upgraded OSIRIS is performed and the simulation results are described.;An idea of advancing beam particles and plasma particles with different time scales is proposed to reduce running time for modeling long scale PWFA. This multiple time scale algorithm is benchmarked with explicit algorithm and QuickPIC algorithm and its limitation is also discussed.;To realize a high-energy e-/e+ linear collider, a new approach for high gradient positron acceleration in a plasma wake is proposed. In this approach, positrons are produced through pair creation as an electron beam traverses a thin foil target embedded within the plasma. Then they are focused and accelerated in the plasma wake excited by the same electron beam after the target. Monte Carlo and 3D PIC simulations shows that a large number of positrons (107∼108) are trapped and accelerated to ∼ 5GeV over 1m with relatively small energy spread and low emittance. Some outstanding physical issues are discussed. Prospects for experimentally testing positron generation and acceleration in the electron wake are also discussed.