Modelling of laser plasma interaction with applications to particle acceleration and radiation generation

Doktorsavhandling, 2019

The development of laser systems with ultra-high intensities has allowed the study of the relativistic interaction of laser light and ionized matter, plasmas, as well as opened up prospects for compact particle accelerators, generation of high intensity X-ray, XUV radiation, and 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. Although analytical work can capture the essence of the dynamics in a range of situations, the rich dynamics in laser-plasma interaction results in that numerical modelling, and in particular the Particle-In-Cell (PIC) method, is critical to gain a detailed description of the dynamics. This is a stochastic method in which phase-space is sampled with macro-particles and allows for efficient modelling of high dimensional problems, but has limitations due to statistical noise.

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 address the problem of implementing efficient continuum methods for the Vlasov-Maxwell system of equations. Furthermore, we treat ion shock acceleration using continuum methods. In the following papers, we address scalings of the electron spectrum in the electron sheath, formed at the vacuum-plasma boundary through the interaction of a relativistic laser and moderately overdense plasma. This is important to determine the spectral properties of high harmonic radiation generated from the laser plasma interaction. We also explore electron wakefield acceleration driven by laser pulses with wavelength in the X-ray regime generated from laser plasma interaction in the moderately overdense regime. By reducing the wavelength, the quantum parameter is enhanced, leading to comparable electron and photon energies already at moderate relativistic amplitudes although with more infrequent emission of photons than at optical wavelengths, preventing radiation losses from becoming a roadblock for the acceleration process.