Laser-driven discharges and electromagnetic fields

When high intensity lasers interact with solid targets, hot electrons are produced that can exit the material and leave behind a positive electric charge. As this accumulated charge is neutralised by a cold return current, radiation is emitted with characteristics dependent on laser and target properties. This thesis examines how electromagnetic radiation is emitted in experiments with long-pulse and short-pulse lasers. Radiofrequency electromagnetic pulses emitted during ps-duration laser interactions can disrupt scientific measurements and damage electronic equipment close to the target. A study of electromagnetic pulses produced by the Vulcan laser is presented. Strong fields exceeding 100kV/m and 0.1mT were measured 1.5m from the target using conducting probes. Scaling of the EMP field with laser and target parameters shows qualitative agreement with target charging models. A novel EMP mitigation scheme is presented using a dielectric spiral target holder. Experimental results are used to benchmark a frequency-domain dipole antenna model of EMP emission that connects charging physics to EMP fields measured at an arbitrary distance from the target. In a separate experiment, coil targets were driven with three ns laser beams from the Vulcan laser, generating multi-tesla quasi-static magnetic fields. Dual-axis proton deflectometry was used to measure electric and magnetic fields around the coils. Results suggest that wire electric fields of order 0.1GV/m develop on a 100ps timescale. Maximum currents of 10kA were observed towards the end of the laser drive for 1mm- and 2mm-diameter loop targets, corresponding to an axial magnetic field of B_0=12T in the 1mm loops. Deflectometry results agree well with a plasma diode model, whereas B-dot probe measurements of the magnetic field were approximately 10x larger. Analytic and computational modelling of charged particle motion in electric and magnetic fields is presented. Prospects for an all-optical platform for magnetized high energy density physics experiments are discussed.