Numerical studies of a plasma accelerator driven free electron laser

Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2020
Thesis identifier
  • T16122
Person Identifier (Local)
  • 201456588
Qualification Level
Qualification Name
Department, School or Faculty
  • The Free Electron Laser (FEL) is a unique source of tunable, coherent light, that is particularly important towards and into the x-ray region of the spectrum. After the achievement of FEL lasing that is based on conventional acceleration utilizing radiofrequency cavities, a significant challenge is the creation of an compact FEL working with an electron bunching accelerated via plasma-based accelerators. However, electron beams produced by some plasma accelerators with large normalized emittance, significant levels of energy spread and energy chirp are a major challenge towards driving FELs. Novel plasma-based acceleration and injection methods, such as beam driven under dense Plasma photocathode Wake-Field Acceleration (PWFA), promises electron beams with ultra-low normalized emittance, high peak currents and low energy spreads. The plasma photocathode injection method is an advanced plasma based electron injector which releases electrons directly inside a PWFA by selectively laser-ionizing a neutral background gas. A 250 MeV electron beam from a PWFA with a fs-scale duration, mmmrad normalized emittance and with a natural negative energy chirp is investigated. This thesis uses simulations to explore the capability of a plasma photocathode to drive an FEL and to investigate the effects of the electron beam energy chirp on lasing. It is shown that removing the energy chirp is a key to enable the high quality beams to achieve FEL lasing. The beam is first used as delivered – with relatively high chirp and then with the chirp removed. The VSim code is used to model the plasma accelerator, and the Puffin code for the FEL process. A dynamically evolving current profile, due to energy chirp changing the electron pulse current profile, induces ballistic bunching at moderate energies. This bunching can generate significant coherent radiation via the process of Coherent Spontaneous Emission (CSE). While this CSE is seen to drive some FEL-induced electron bunching at the radiation wavelength, the dynamic evolution of the energy chirped pulse dampens out any high-gain FEL bunching interaction. When the beam energy chirp was removed numerically, the FEL was shown to lase via the high-gain FEL interaction and exponential gain was demonstrated. Therefore, if the energy chirp of the beam can be reduced experimentally, and on-going research is suggesting this is possible, this opens the prospect of a future PWFA FEL operating in the high-gain regime.
Advisor / supervisor
  • McNeil, B.
  • Khalil, Sherif Mohamed
Resource Type