Azimuthal current density distribution resulting from a power feed vacuum gap in metallic liner experiments at 1 MA

Summary form only given. We present a study investigating the distribution of current density in solid, metallic liners directly relevant to the MagLIF approach to fusion. Here, the liner thickness is large compared to the collisionless skin depth, and a vacuum gap is introduced in the power feed to simulate the load method on the Z machine at Sandia Laboratories. We present optical emission data along with a 3D magnetic field mapping method from aluminum liner loads on the 1 MA, 100ns COBRA generator. The relative strength of the magnetic field at 4 azimuthal locations and 3 axial heights allow inference of the distribution of current density in the liner as a function of space and time. Results show that current density is azimuthally non-uniform throughout the current drive and evolves slowly on the timescale of the experiment. The azimuthal current density profile typically correlates with axial optical images evolution of `hot-spots' generated from breakdown vacuum gap which show similar evolution as the experiment proceeds. Such non-uniformities will have a substantial effect on liner implosions for fusion is they persist at higher current. Additionally, the location of plasma initiation can be pre-determined by preferentially closing the vacuum gap at one azimuthal position, which provides a useful initial set-up for comparison to magnetohydrodynamic simulations using the Gorgon code. This allows examination of the mechanisms controlling the azimuthal current distribution and allows estimation of the extent to which this may affect Z and higher current liner experiments.