HIGH REPETITION RATE LASER-DRIVEN ELECTRON ACCELERATION TO MEGA-ELECTRON-VOLT ENERGIES
Milchberg, Howard M
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Laser-driven particle accelerators have the potential to be a compact and cost-effective replacement for conventional accelerators. Despite the significant achievements of laser wakefield acceleration in the last two decades, more work is required to improve the beam parameters such as the energy spread, emittance, repetition rate, and maximum achievable energy delivered by these advanced accelerators to values comparable to what conventional accelerators offer for various applications. The goal of this dissertation is to lower the threshold of the laser pulse energy required for driving a wakefield and in turn enable higher repetition rate particle acceleration with current laser technology. In the first set of electron acceleration experiments presented in this dissertation, we show that the use of a thin gas jet target with near critical plasma density lowers the critical power for relativistic self-focusing and leads to electron acceleration to the ~MeV range with ~1pC charge per shot, using only ~1mJ energy drive laser pulses delivered by a 1kHz repetition rate laser system. These electron beams accelerated in the self-modulated laser wakefield acceleration (SM-LWFA) regime have a thermal energy distribution and a rather large divergence angle (>150mrad). In order to improve the energy spread and the divergence, in the second set of the experiments, we employ a few-cycle laser pulse with a ~7fs duration and ~2.5mJ energy as the driver, to perform wakefield acceleration in the bubble regime using near critical plasma density targets. The results show a significant improvement in the energy spread and divergence of the beam. The electron bunches from this experiment have a quasi-monoenergetic peak at ~5MeV with an energy spread of ΔE/E≃0.4 and divergence angle of ~15mrad. These results bring us closer to the use of tabletop advanced accelerators for various scientific, medical, and industrial applications.