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Title: Laser plasma accelerator and wiggler
Author: Kneip, Stefan
ISNI:       0000 0004 2685 1778
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2010
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This thesis details experimental research of laser-driven electron acceleration from underdense plasmas and the characterisation of the x-ray radiation owing to the transverse oscillatory motion that electrons perform during the acceleration process. Acceleration of monoenergetic electron beams to the GeV level was achieved for the first time in a self-guiding, self-injecting wakefield accelerator in the nonlinear regime, driven by the 200 TW Astra Gemini laser. The laser pulse was shown to be self-guided for 1 cm or more than ten times its Rayleigh range, by measurement of a single filament containing > 30% of the initial laser energy at this distance. The intensity in the guided filament is amplified beyond its initial value, as suggested by the GeV electron energy gain. Three dimensional numerical modeling is in excellent agreement with the experimental findings. In this regime, a beam of tens of keV x-rays emanating from a micrometer source with milliradian divergence, spatial coherence and a peak brightness comparable to third generation light sources was measured on experiments with the 100 TW Hercules laser. The measurements show that, due to their small transverse oscillations, the electron trajectories and their radiation properties resemble the scenario of an electron in a wiggler-type insertion device, with a strength parameter K close to 1. The experimental findings are supported by three dimensional modeling of the electron and x-ray beam. Betatron radiation was also measured with ten times longer and more intense pulses from the Vulcan Petawatt laser. In this case, electron acceleration is strongly driven transversely by the laser and a betatron resonance leads to a tenfold increase in oscillation amplitude. This alters the characteristics of the emitted synchrotron radiation fundamentally, increasing 50-fold the strength parameter and divergence, 10-fold the source size and up to 5-fold the x-ray energy, thereby broadening the electron energy distribution and converting up to 5% of their energy into x-rays. The studies provide evidence for the scalability of self-guided laser wakefield accelerators from 0.1 to 1 GeV. Furthermore the work demonstrates that betatron radiation can help to understand the acceleration process and has characteristics comparable to conventional synchrotron light.
Supervisor: Najmudin, Zulfikar Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral