UCL Discovery

## Generating brilliant X-ray pulses from particle-driven plasma wakefields

Holloway, JA; (2015) Generating brilliant X-ray pulses from particle-driven plasma wakefields. Doctoral thesis , UCL (University College London).

## Abstract

This thesis presents a simulation campaign that demonstrates for the first time, that by micro-bunching the Diamond Light Source electron beam, X-ray pulses with peak brightnesses of B = 3.2 x 10^{28} photons^{-1}s^{-1}mm^{-2}mrad^{-2}0.1%BW$^{-1} at E = 50 keV are produced. The production mechanism ensures the pulses are radially polarized on creation. These properties allow for a smaller focal spot, overcoming the limit due to diffraction, providing a unique new probe for individual atomic excitations by the utilisation of the longitudinal component of the electric field. We also demonstrate that the micro-bunched electron beam is an effective wakefield driver in itself, able to accelerate a witness electron beam to higher energies, providing a potential new route to reliable X-ray free electron laser generation. An experiment was performed using the$E = 600$mJ,$\tau = 40\$ fs Astra laser at the Central Laser Facility testing a novel single-shot parasitic plasma diagnostic. The photon acceleration effect on the driving laser pulse was utilised to determine the plasma density. Strong modulation to the long laser pulse's intensity profile were measured at the plasma wavelength, capturing the self-modulation effect on the long laser pulse. The results show a linear relationship between the diagnosed plasma density and the known pressure within the gas target and are supported by numerical simulations. The diagnostic requires no dedicated probe pulse but instead simply requires the driving laser pulse to be several plasma periods long, allowing for a cost effective, simple to implement diagnostic.

Type: Thesis (Doctoral) Generating brilliant X-ray pulses from particle-driven plasma wakefields University College London An open access version is available from UCL Discovery English plasma wakefield, X-ray, particle driven, X-rays, particle driven plasma wakefield, photon acceleration, plasma diagnostic UCLUCL > Provost and Vice Provost OfficesUCL > Provost and Vice Provost Offices > UCL BEAMSUCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical SciencesUCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy https://discovery.ucl.ac.uk/id/eprint/1473045