Electron and Proton Acceleration Using the 30 TW, 30 fs Hercules Laser.

[摘要] This thesis presents experimental measurements of energetic particles accelerated from a high intensity, short pulse interaction with underdense and overdense plasmas.From the interaction of a 40 TW laser pulse with an underdense He plasma, high energy (150 MeV), highly directional ($sim$10 mrad) relativistic electron beams are used to perform photonuclear activation ($gamma$,n) of carbon and copper and photofission ($gamma$,f) of uranium.Monte-Carlo simulations show the bremsstrahlung produced by these quasi-monoenergetic electrons in heavy converters includes a large number of MeV $gamma$-rays used to excite the giant dipole resonance.Due to the quasi-monoenergetic nature of the wakefield accelerated electrons, photonuclear activation was enhanced between one to two orders of magnitude compared to previous experiments.In a separate series of experiments proton generation from the interaction of a high intensity, high contrast laser incident upon submicron foils was described.The maximum proton energy from transparent dielectrics is shown to depend on the hydrogen content of the target material and not on the targets thickness.PIC simulations are used to show a two stages acceleration mechanism consisting of:(1) proton acceleration due to a ponderomotively induced charge separation at the front surface and (2) an additional acceleration due to the target normal sheath.The observed effect was experimentally distinguished through target selection of hydrogen and non-hydrogen containing materials.It was observed that the maximum proton energy for hydrogen containing targets such as Mylar and CH was two times higher than for non-hydrogen containing targets such as Si$_{3}$N$_{4}$.Finally, a relativistic plasma shutter technique was proposed and tested to further increase the laser contrast.This is done by placing a thin foil before the target with a unique thickness such that the leading edge of the laser fully ionizes the foil causing it to expand into an underdense plasma.PIC simulations show a high intensity, high contrast laser strongly deforms a thin target ($<$ 70 nm) causing the accelerated protons to shift away from the target normal and towards the laser axis.The protons characteristic shift toward the laser axis was observed after inserting a plasma shutter before a 50 nm target.

[发布机构] University of Michigan

[效力级别] Electron Acceleration

[关键词] High Intensity Laser;Electron Acceleration;Proton Acceleration;Physics;Science;Applied Physics