Exploring extreme magnetization phenomena in directly-driven imploding cylindrical targets

TL;DR

This study uses advanced MHD simulations to investigate highly magnetized plasma regimes in cylindrical implosions, focusing on magnetic flux compression, diagnostic techniques, and the effects of magnetization on implosion dynamics.

Contribution

It introduces a detailed analysis of extreme magnetization phenomena in cylindrical implosions, including diagnostic methods and optimization strategies for experiments.

Findings

Magnetic fields exceeding 10 kT can be achieved in implosions.

Spectroscopic diagnostics can measure core density and temperature.

Magnetization influences implosion stability and energy distribution.

Abstract

This paper uses extended-magnetohydrodynamics (MHD) simulations to explore an extreme magnetized plasma regime realisable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10~kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally-driven or current-driven transport is dominating.