Magnetically driven flyer launch optimisation*

We present multi-point velocity measurements for 1cm scale flyer plates launched using the 1MA MACH facility at Imperial College London. Magnetically driven flyer plate impact is of interest for material equation of state research, and more recently for a novel fusion ignition scheme. Generation of the desired planar shock is dependent on maintaining a flat flyer face, with the front surface of the flyer in a solid state at impact. However, flatness can be compromised by material effects and non-uniform magnetic field, while melting can be caused by formation of shocks within the flyer or joule heating related to the magnetic field.

We show results of planar 1cm² Al flyers diagnosed using 6-point Photon Doppler Velocimetry (PDV) to probe velocity across a width of 3mm on the flyer to return front surface uniformity and qualitative reflectivity data. Maximum velocity of 3000ms^-1 was achieved with a flyer of thickness 0.3mm, at maximum current of 991kA. Velocity variation along the direction of current through the flyer was found to be ~6% over 3mm.  2D simulations, performed in COMSOL, of both equivalent and novel non-planar geometries, are also presented.