Universal Scaling of the Electron Distribution Function in Relativistic Laser Plasma Interactions (Dr. Sherlock)

Dr. Sherlock – We provide a formula for the distribution function of energetic electrons which
stream in the forward direction when a relativistic ally-intense laser pulse irradiates a short-scalelength dense plasma at normal incidence. If the energy absorption fraction is known, the entire function can be characterized in terms of the laser intensity. A number of important characteristics can then be obtained, including the fast electron energy, current density and angle of ejection. We suggest an objective means for calculating the fast-electron energy which is approximately given by ~0.6 of the vacuum oscillatory energy. This reduction in energy is shown to be consistent with the energy required to draw a return current.

Dr. Ridgers – Vlasov-Fokker-Planck (VFP) simulations provide a novel tool for investigating laserplasma interactions with long and short laser-pulse durations. When applied to long-pulse
interactions they can correctly describe non-local transport and B-field dynamics; both important in
hohlraums. In short-pulse solid-density simulations VFP codes describe the high degree of
anisotropy of the distribution function while accurately modelling collisions. We used IMPACTA to
model ns interactions for plasmas in large (12T) externally generated B-fields. Results
demonstrated the suppression of non-locality by B-fields and their rapid advection caused by the
Nernst effect (seldom considered in simulations). We will also discuss VFP modelling of shortpulse
interactions using FIDO. The generation of large B-fields at the target rear-surface confines
fast electrons, likely modifying rear-surface probe measurements.
Dr. Mark Sherlock is a theoretical plasma physicist from Imperial College London (ICL) where he received his PhD (supervised by Prof. M. Haines) and was a post-doctoral researcher. He joined the Central Laser Facility at Rutherford Appleton Laboratory in 2005 and returned to ICL in 2009. His research interests include fast electron transport, fast ignition, beam fusion and Z-pinches.

Dr. Chris Ridgers is a theoretical plasma physicist from ICL and post-doctoral researcher on the HiPER project. His 2008 PhD thesis (supervised by Dr. R. Kingham) addressed hydrodynamic modeling of implicit VFP plasma transport.