Observations of the magneto-Rayleigh-Taylor instability and shock dynamics in gas-puff Z-pinch experiments

Abstract

We describe a series of experiments performed to study the shock structure generated during the implosion of a gas-puff Z-pinch. The Z-pinch is produced by a double-annular gas-puff with a center jet driven by Cornell University's COBRA generator operating with a 1 MA, 200 ns current pulse. Using 532 nm laser interferometry and 100 MHz multi-frame cameras, a shock structure is observed to form early in the implosion. The shock appears to be created by a current layer at the outer radius of the imploding plasma which acts as a piston moving inward at several hundred km s−1. The dynamics of the shock and its radial position ahead of the piston agree well with a simple uniform density model outlined in the study by Potter [Nucl. Fusion 18(6), 813 (1978)]. The outer surface of the current layer is observed to be Magneto-Rayleigh-Taylor unstable. The growth rate of this instability is found to depend on the radial density profile of the material within the layer of high-density fluid between the shock and the piston, as predicted by recent theoretical work [see, e.g., D. Livescu, Phys. Fluids 16(1), 118 (2004)]. Growth rates measured in krypton implosions, where the post-shock material is found to decay quasi-exponentially away from the piston, were more than ten times smaller than those recorded in otherwise identical implosions in argon plasmas, where the material between the shock and the piston was observed to maintain a uniform density.

Effect of tailored density profiles on the stability of imploding Z-pinches at microsecond rise time megaampere currents

“…On the one hand, this flash could be associated with a shock wave arrived at the axis. Such a shock wave, as shown in [35][36][37][38], can move away from the current sheath (acting as a magnetic piston) for a distance of 0.5-1 cm. On the other hand, the bright flash could occur due to the arrival of light ions at the pinch axis.…”

Magnetic Rayleigh–Taylor Instability in an Experiment Simulating a Solar Loop

“…Previous experiments (Lebedev et al 1998;Sinars et al 2010;de Grouchy et al 2018) investigated the MRTI using Zpinch implosions, but these experiments focused mainly on the growth rate and X-ray production and did not vary the magnetic field to test for a relation between magnetic field and the MRTI wavelength.…”

Plasma Waves and Rayleigh–Taylor Instability: Theory and Application

“…To study the difference between growth of perturbation and geometry effect at the equator and pole, they use the Gaussian-type and cosinetype perturbation [106]. Grouchy et al experimentally investigated gas-puff Z-pinch implosion and studied Magneto RTI in the cylindrical shocks launched toward the symmetry axis in different plasma of argon and neon [107]. Li et al developed a code based on Euler method called as massively parallel laser ablative RTI code using simulations by considering the laser energy deposition, hydrodynamics and the electronic thermal conductivity [108].…”