Models of x-rays and electron beams from laser wakefield accelerators
File(s)
Author(s)
Hughes, Adam
Type
Thesis
Abstract
This thesis focuses on electron and radiation beams produced in laser wakefield accelerators (LWFAs). The first part presents two radiation computation codes (RCCs) built to model x-ray beams from LWFAs. One RCC models the temporal intensity profile and photon fluence spectrum at different positions. The other RCC models the angular energy density distributions. Six experiments were modelled. The modelled radiation beams have a duration between 40 and 100 fs, a peak spectral fluence of 3x10^2 to 7x10^4 photons/mrad^2/0.1% bandwidth (BW) and a peak brightness of 2x10^21 to 6x10^22 photons/s/mrad^2/mm^2/0.1% BW. The modelled angular energy density distributions are compared with experimental results and discussed.
The second part considers simulating an LWFA for future light source applications. A machine learning algorithm was used to optimise the peak energy and total charge from simulated LWFAs driven by a 30 mJ, 7.5 fs laser. In optimising the peak energy, the algorithm primarily adjusted the plasma density, plasma length, laser focal position and plasma density up-ramp length. The optimised electron beams had a local maximum in their spectra at 125 MeV. Optimising the total charge, the algorithm adjusted the plasma density, up-ramp length, laser focal position and spectral phase coefficients. The optimised electron beams had a total charge of 200 pC above 10 MeV.
Finally, an experiment was performed using a 44 mJ, 12 fs laser pulse to drive LWFAs at a 10 Hz repetition rate. The first electron beams produced with this system are reported, with energies of up to 60 MeV and a total detected charge between 2.0 and 3.5 fC above 10 MeV. In scans of the plasma density and focal position, electron beams with the highest energy and charge were produced at plasma densities of 4.5x10^19 cm^-3 when focusing the laser at least 0.2 mm into the plasma.
The second part considers simulating an LWFA for future light source applications. A machine learning algorithm was used to optimise the peak energy and total charge from simulated LWFAs driven by a 30 mJ, 7.5 fs laser. In optimising the peak energy, the algorithm primarily adjusted the plasma density, plasma length, laser focal position and plasma density up-ramp length. The optimised electron beams had a local maximum in their spectra at 125 MeV. Optimising the total charge, the algorithm adjusted the plasma density, up-ramp length, laser focal position and spectral phase coefficients. The optimised electron beams had a total charge of 200 pC above 10 MeV.
Finally, an experiment was performed using a 44 mJ, 12 fs laser pulse to drive LWFAs at a 10 Hz repetition rate. The first electron beams produced with this system are reported, with energies of up to 60 MeV and a total detected charge between 2.0 and 3.5 fC above 10 MeV. In scans of the plasma density and focal position, electron beams with the highest energy and charge were produced at plasma densities of 4.5x10^19 cm^-3 when focusing the laser at least 0.2 mm into the plasma.
Version
Open Access
Date Issued
2024-01
Date Awarded
2024-06
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Najmudin, Zulfikar
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)