Auto-magnetizing liners for MagLIF experiments

Magnetized Liner Inertial Fusion (MagLIF, [1]) is an inertial confinement fusion concept that includes a strong magnetic field embedded in the fuel to mitigate thermal conduction loss during the implosion. Magnetization of the target in MagLIF experiments on Sandia's 20 MA Z Machine has traditionally required an external pair of field coils in a Helmholtz-like configuration [2]. The novel AutoMag concept employs a composite liner (cylindrical tube) with helically oriented conduction paths separated by insulating material to provide both axial premagnetization of the fuel (during a slow rising current pre-pulse) and fuel compression (during a fast rising main current pulse). This integrated axial field production mechanism offers a few potential advantages when compared to the external field coils currently being used on Z. AutoMag seeks to increase drive current for MagLIF experiments by decreasing the transmission line inductance, provide higher peak axial field levels (>30 T) inside of the liner without compromising diagnostic access, and offer new mirrored magnetic field topologies within the fuel column. 3D electromagnetic simulations using ANSYS Maxwell have been completed in order to explore the current distributions within the helical conduction paths, the inter-wire dielectric strength properties, and the thermal properties of the helical conduction paths during a nominal premagnetization phase (∼1 MA in 100ns). Initial designs show a broad range of peak Bz from 20 T to 100T in single helix configurations before breakdown field levels in the dielectric become a concern due to increasing aggressiveness of the helical pitch. Stacked helix designs show capability to provide mirror field topologies with peak Bz near the top and bottom of the liner and mirror ratios (Bzmax/Bzmin) approaching 1.5. These designs will soon be tested in experiments (∼1 MA, 100ns) seeking to measure Bz(t) inside of the liner and assess failure mechanisms. Simulations of implosion dynamics for several AutoMag liner designs have been completed using the 3D MHD code Gorgon [3] to evaluate the effects of conductor/insulator material choice and the quality of implosion symmetry for this concept.