Quasistationary magnetic field generation with a laser-driven capacitor-coil assembly

Abstract

Recent experiments are showing possibilities to generate strong magnetic fields on the excess of 500 T with high-energy nanosecond laser pulses in a compact setup of a capacitor connected to a single turn coil. Hot electrons ejected from the capacitor plate (cathode) are collected at the other plate (anode), thus providing the source of a current in the coil. However, the physical processes leading to generation of currents exceeding hundreds of kiloamperes in such a laser-driven diode are not sufficiently understood. Here we present a critical analysis of previous results and propose a self-consistent model for the high current generation in a laser-driven capacitor-coil assembly. It accounts for three major effects controlling the diode current: the space charge neutralization, the plasma magnetization between the capacitor plates, and the Ohmic heating of the external circuit-the coil-shaped connecting wire. The model provides the conditions necessary for transporting strongly super-Alfvenic currents through the diode on the time scale of a few nanoseconds. The model validity is confirmed by a comparison with the available experimental data.

Proton deflectometry of a capacitor coil target along two axes

“…This is ∼100 × lower than that quoted for experiments at LULI [8,16] , though the discrepancy can be explained by a lower hot electron temperature. On Vulcan, we were operating at 20 × lower intensity than LULI, and T e = T e (I λ 2 ) is an important parameter governing the loop current in theoretical models of capacitor coils [2,6,37] .…”

“…Although we used a layer of CH plastic to try to enhance the hot electron temperature, the measured current/magnetic field was actually slightly lower when using plastic coated targets. Since the loop current is thought to vary sensitively with T e [2,6,37] , this suggests that the plastic layer did not increase the hot electron temperature.…”

“…Capacitor coils are a type of laser-driven solenoid that consists of two metal plates held in parallel, connected by a loop of wire or metallic ribbon [1][2][3] . A high-energy laser beam is used to accelerate hot electrons [4,5] from the rear plate (anode) onto the front plate (cathode) [6] . A return current is then established along the connecting loop, generating a quasi-static magnetic field that can be used in high energy density physics experiments [2,7,8] .…”

Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics

“…In summary, and according to our model detailed in Ref. 28 , three physical aspects are important to explain the intense discharge currents measured experimentally: the charge neutralization and the flattening of the potential distribution between the two plates, the ion inertia allowing for neutralized electron transport with currents far above the Alfvén limit, and the maximum temperature of the wire due to the latent heat of vaporization. The main control parameter is the hot electron temperature, which mainly ensues from the laser irradiance, I las λ 2 las .…”

Laser-induced extreme magnetic field in nanorod targets

“…The only source capable of generating such an ultra high magnetic field from lasermatter interactions is the return current of electrons flowing in the skin layer of plasma surfaces. This has been exploited to generate mega gauss magnetic fields on macroscopic scale [1,2] or in laser-plasma interactions near the laser focal spot [3][4][5]. A single nanorod has been predicted to be able to induce an even gigagauss magnetic field.…”