Modelling of laser plasma interaction with applications

Licentiatavhandling, 2018

The development of laser systems with ultra-high intensities has both opened up prospects for compact particle accelerators, as well as probing QED-effects, which are present in the high intensity regime. To describe laser matter interaction, it is necessary to self-consistently account for the paths of a large number of particles and the corresponding electromagnetic fields, with the addition of stochastic effects at high laser intensities. The primary method for modelling laser plasma interaction is the Particle-In-Cell (PIC) method, a Monte-Carlo method which samples phase-space with macro-particles and allows for efficient modelling of high dimensional problems. However, for some applications, for example shock acceleration and instability growth, continuum methods, i.e. solving the Vlasov-Maxwell system of equations on a phase-space grid, may be preferable to accurately describe the plasma dynamics. In the first two papers in this thesis, we adress the problem of implementing efficient continuum methods for the Vlasov-Maxwell system of equations. Furthermore, we treat ion shock acceleration using continuum methods.

This thesis also contains an investigation of the prospects for driving electron wakefield acceleration using coherent X-ray pulses. Recent advances in the theory for generation of high harmonics indicate the feasibility of relativistic amplitude coherent X-ray pulses, which could be used to drive a wakefield in a solid density plasma. We show by PIC-simulations, incorporating QED-effects, that similarity scaling laws hold for the wavelength 5 nm and moderate relativistic amplitudes in the range 10 to 100. The quantum parameter is shown to be enhanced, leading to comparable electron and photon energies already at modest relativistic amplitudes although with more infrequent emission of photons than at optical wavelengths, preventing radiation losses from becoming a roadblock for the acceleration process.