title: Charged particle beam acceleration and strong discharge currents' fields generation by laser - a study on laser-driven ion sources and beam transport suited for application in high-energy-density physics experiments
Creators: name: Ehret, Michael
Publisher: name: UNSPECIFIED
Year: 2022

description: This work aims at both, the experimental benchmark of laser-driven ion acceleration from targets in the near-critical density regime and the exploration of laser-driven open-geometry platforms for spatial and spectral ion beam tailoring. Theoretically described mechanisms and dynamics predicted by numerical simulations are compared to novel experimental findings that are supported by new particle in cell simulations and heuristic models. Results comprise (i) demonstration of Helium ion acceleration from ultra-relativistic laser-driven near-critical density gas jet targets employing shock nozzles, (ii) further investigation of the driving mechanisms of charged particle beam lensing platforms in the quasi-static regime driven by ns-laser and in the transient regime driven by sub-ps laser, and (iii) studies of transport and tailoring of laser accelerated particle beams by electromagnetic and magnetic fields. The Helium ion source shows cut-off energies above 55MeV, a regime suitable for isotope production in alpha-therapy. Hence, the destruction of nozzles in the violent experimental environment and the perspective to high-repetition-rate operation underlines the need of mass producible nozzles with automatized nozzle exchange and vacuum systems able to maintain good vacuum levels. Ns-laser driven magnetic lenses show comparable current amplitudes in the spontaneous magnetic fields of the plasma and the consumer loop, which favors the theoretical modeling of the platform as a plasma-diode power source. During the laser drive, space charge effects arise with the arrival of the laser-plasma in vicinity of the magnetic lens, representing a possible threat to efficient lensing of ion beams. A modified target geometry is presented that decreases space charge effects. Short laser-pulse driven solid target discharge gives rise to a surficial pulsed potential dynamics guided by the target geometry. This work shows that electromagnetic discharge pulses emanating the interaction region are followed by a pulse discharge current from the ground, both transporting kA-range currents through the target rod. The observed pulsed current dynamics on timescales of tens of ps indicates the presence of a hot surface plasma. The temperature and electron density of the surface plasma are promising control parameters of the discharge pulse dispersion. The high branch of the dispersion relation is responsible for a group velocity different from the speed of light. Solutions on the low branch of the dispersion relation agree with modulations of the target potential in their spatial dimensions and temporal growth rate. Experimental and numerical studies of short laser pulse driven platforms show their applicability to spectral shaping of ion beams, with a perspective to temporal compression of beams for cases where low energy parts of the spectrum get efficiently post-accelerated. Presented are the experimental study of a simple double-coil geometry and a numerical study of a helical coil target. This work motivates junction of presented approaches for future experiments aiming at high repetition rate laser accelerated high energy density ion beams for applications, notably medical isotope production, or fundamental research, ranging from studies on collective stopping effects, warm dense matter generation to an optimized fast ignition particle injector.