Stabilization of gas puff Z-pinch implosions by using external Bz field on COBRA

Summary form only given. We present investigations of gas puff Z-pinch implosions with an applied external Bz field. The experiments are conducted on the 1-MA, 200-ns COBRA generator. Stabilized 200-ns, high current z-pinch implosions have been demonstrated by using double or triple-gas puffs. In the experiments, a triple-nozzle is used to produce z-pinch loads with concentric outer, inner and center gas puff columns. Implosion dynamics are studied for triple- or double-(without inner puff) gas puffs with or without an external Bz field. In these multi-nozzle gas puff z-pinches, a heavier inner gas puff decelerated the implosing plasma resulting in stabilization of the Magnetic Rayleigh-Taylor (MRT) instability. More unstable implosions were observed with a lighter inner gas puff. Application of a several kG external axial Bz field produce magnetic shear, which also mitigate the MRT instabilities. We use a three-frame Laser Shearing Interferometer (LSI) and a two-frame Laser Wavefront Analyzer (LWA) to measure the plasma density profiles and an 8-frame 2-ns gated EUV camera to image the imploding plasma. From measurements, the structures of the imploding plasma sheath and MRT instability are determined. Details will be presented in the report.