Jeremy Hill

Laser generated proton beam focusing and high temperature isochoric heating of solid matter

The results of laser-driven proton beam focusing and heating with a high energy (170J) short pulse are reported. Thin hemispherical aluminum shells are illuminated with the Gekko petawatt laser using 1μm light at intensities of ∼3×1018W∕cm2 and measured heating of thin Al slabs. The heating pattern is inferred by imaging visible and extreme-ultraviolet light Planckian emission from the rear surface. When Al slabs 100μm thick were placed at distances spanning the proton focus beam waist, the highest temperatures were produced at 0.94× the hemisphere radius beyond the equatorial plane. Isochoric heating temperatures reached 81eV in 15μm thick foils. The heating with a three-dimensional Monte Carlo model of proton transport with self-consistent heating and proton stopping in hot plasma was modeled.

Beam-Weibel filamentation instability in near-term and fast-ignition experiments

High intensity laser-plasma interactions accelerate electrons to suprathermal velocities. Their current is neutralized by an induced cold electron return current. These inter-penetrating and anti-parallel currents are subject to electrostatic and electromagnetic instability. Two analytical models for electron transport are used to predict the growth rates of the linear electromagnetic beam-Weibel filamentation instability in both near-term laser-solid experiments as well as in future fast-ignition experiments. Specifications and calculations of the relevant physical parameters are made. Both models predict that instability growth is significant for the fast-ignition case. Instability development in near-term experiments is also significant, but with a greater difference between the models’ predictions at low densities.