VISAR 'cross-hairs': Simultaneous perpendicular line-imaging VISAR

Abstract

Often the velocity measured at the rear surface of a dynamic compression target varies spatially, caused for instance by the tilt/curvature of a gas gun flyer, asymmetries in the magnetic field on a pulsed power driven experiment, or meso-scale heterogeneous targets. One way to monitor this in an experiment is to employ multiple point velocimetry techniques, but even with multiplexing this can become expensive in terms of hardware, in particular high speed sensors and scope channels. We report on the initial development of a multi-axis line-imaging VISAR system, which will record the spatial velocity along two orthogonal directions. Cylindrical optics are used to project a set of cross-hairs onto the target, maximising the use of input laser light; we then describe the image relay, interferometer configuration and alignment. This 'quasi' two dimensional system will become one of the principal diagnostics on the MACH (Mega Ampere Compression and Hydrodynamics) facility at Imperial College London, where the multi-axis measurement will help optimise strip-line design to achieve uniform ramp compression of targets.