Instability growth for magnetised liner inertial fusion seeded by electro-thermal, electro-choric and material strength effects

摘要

Magnetised liner inertial fusion (MagLIF) represents a promising pathway to controlled thermonuclear fusion which would provide clean, plentiful energy. The concept uses a pulsed power machine to implode a metal cylinder or `liner' containing pre-magnetised and preheated fusion fuel; a critical limitation of such systems is the magneto-Rayleigh-Taylor (MRT) instability which primarily disrupts the outer surface of the liner.ududWe carried out 3D simulations using Gorgon, an Eulerian resistive MHD code, to match experimental results showing large amplitude multi-mode MRT instability growth resulting from MagLIF-relevant liner implosions. These simulations under-estimated MRT amplitudes and wavelengths near stagnation due to a lack of azimuthal correlation, achieving good agreement only with the addition of an artificially azimuthally correlated initialisation. The experiment was repeated with an axial magnetic field, resulting in re-orientation of the MRT instability into a helical structure which has yet to be explained.ududWe have shown that the missing azimuthal correlation could be provided by a combination of the electro-thermal instability (ETI) and an `electro-choric' instability (ECI); describing respectively the tendency of current to correlate azimuthally early in time due to temperature dependent Ohmic heating; and an amplification of the ETI driven by density dependent resistivity around vapourisation.ududWe developed and implemented a material strength model to improve simulation of the solid phase of liner implosions and present test problems and benchmarking against the hydrodynamics code iSALE. Applied to simulations exhibiting the ETI and ECI, the inclusion of strength gave a significant increase in wavelength and amplitude of the ETI and ECI. Full circumference simulations of the multi-mode MRT instability provided a significant improvement on previous randomly initialised results and approached agreement with experiment. Simulations including an axial magnetic field reproduced helical structures associated with azimuthal currents induced by magnetic field compression, but did not reproduce experimental results.