Axial magnetic field injection into thick, imploding liners

TL;DR

This paper proposes a method to generate the necessary axial magnetic field in MagLIF fusion experiments by using current post configurations, eliminating the need for bulky coils and overcoming skin effect limitations.

Contribution

It introduces a novel approach to produce axial magnetic fields in thick liners by leveraging resistivity gradients, simplifying the setup and reducing inductance issues.

Findings

Resistivity gradients enable faster magnetic field penetration.

Return current posts can replace traditional coils effectively.

Magnetic field of 30T achieved without bulky coils.

Abstract

MagLIF is a fairly new fusion concept using a puled-power generator as the main driver. This concept uses a Z-pinch configuration where the implosion is driven by the Z-machine using 27 MA of electrical current in 100 ns. Since the implosion time is long compared to the heat diffusion time of a non-magnetized plasma, MagLIF requires an initial axial magnetic of 30T to reduce heat losses to the liner wall. Since the field needs to penetrate the transmission lines of the pulsed-power generator, as well as the liner itself, the rise time must exceed tens of microseconds. Any coil capable of producing such field on that long a pulse-length is inevitably bulky. The space required to house the coil near the liner increase the inductance of the load, which becomes problematic since the voltage at the load cannot exceed what the driver can already provide. Yet, the enormous amount of current that the Z-machine can provide could be used to produce the required 30 T by tilting the current posts surrounding the liner. However, the field penetration is limited by the skin effect of the liner wall. This paper shows that when current densities are large enough, the material generate resistivity gradients which forces the current to diffusive across the liner wall much fast than the skin time. As a result, the 30T coil can be eliminated and replaced by return current posts with minimal helicity.