Magnetic Flux Compression of Helical Instability Modes on Imploding Gas Liners*

The Magneto Rayleigh-Taylor instability (MRTI) is a concern for magnetized, imploding z-pinch configurations such as the magnetized liner inertial fusion (MagLIF) concept being studied on the Z facility at Sandia National Laboratories [1]. In MagLIF, MRTI degrades the assembly and confinement of thermonuclear fuel. A key component to MagLIF experiments is the pre-embedded axial magnetic field, which reduces thermal conduction losses during the implosion and traps charged fusion products at stagnation. This axial field modifies MRTI, generating helical plasma striations on the liner surface. The observed pitch angle of the helices is significantly larger than what was originally anticipated. It is hypothesized that the amplification of axial magnetic field, from flux compression occurring in a low-density plasma (LDP) surrounding the liner, could explain the large pitch angle [2]. 

To investigate this hypothesis, a platform is developed to study axial flux compression in LDP on the University of Michigan’s MAIZE facility, a 1-MA class linear transformer driver.  This platform uses MAIZE to implode a low-density gas-puff plasma onto an electrically thick metallic center rod. The resulting MRTI structure, with and without a pre-applied axial magnetic field, was observed with a 12-frame optical self-emission camera as well as visible laser-based diagnostics such as laser schlieren and a laser interferometer system. The results of this study will be presented.