HYDROMAGNETIC RAYLEIGH-TAYLOR INSTABILITY IN HIGH-VELOCITY GAS-PUFF IMPLOSIONS

Experiments using the Saturn pulsed power generator have produced high -velocity z-pinch plasma implosions with velocities over 100 cm/mu s u sing both annular and uniform-fill gas injection initial conditions. B oth types of implosion show evidence of the hydromagnetic Rayleigh-Tay lor instability with the uniform-fill plasmas producing a more spatial ly uniform pinch. Two-dimensional magnetohydrodynamic simulations incl uding unsteady flow of gas from a nozzle into the diode region have be en used to investigate these implosions. The instability develops from the nonuniform gas flow held that forms as the gas expands from the i njection nozzle. Instability growth is limited to the narrow unstable region of the current sheath. For, the annular puff the unstable regio n breaks through the inner edge of the annulus increasing nonlinear gr owth as mass ejected from the bubble regions is not replenished by acc retion. This higher growth leads to bubble thinning and disruption pro ducing greater nonuniformity at pinch for the annular puff. The unifor m puff provides gas to replenish bubble mass loss until just before pi nch resulting in less bubble thinning and a more uniform pinch.