Feedout coupling of Richtmyer–Meshkov and Rayleigh–Taylor instabilities in stratified, radiation-driven foils

Abstract

Coupling between Richtmyer–Meshkov- and Rayleigh–Taylor-unstable surfaces of indirectly driven, stratified, planar foils composed of an aluminum ablator and a beryllium payload carrying a machined initial perturbation was studied using radiographic techniques. The beryllium was transparent to the x-ray backlighter, allowing clear observation of the perturbation transport into the aluminum. The maximum perturbation amplitude (areal–mass difference) was smaller in the aluminum/beryllium foils than in equivalent pure aluminum foils, which could have been the result of shorter growth time, a lower differential acceleration coupling, or the density discontinuity at the aluminum/beryllium interface. Second and third harmonics were not observed in the composite foils.

Feed-out of Rear Surface Perturbation due to Rarefaction Wave in Laser-Irradiated Targets

“…The higher harmonics turn into "positive" phase in later time because of nonlinear saturation of the RT growth. Similar results have been observed in previous experimental works in the x-ray drive experiments [5], but the origin of the higher harmonics before the rarefaction breakout was not given. We consider that the growth of the rear surface perturbation causes the higher harmonics because of the coupling of a vortex and the Richtmyer-Meshkov instability [14].…”

“…When the rarefaction front is rippled, a perturbation arises on the laser-irradiated surface because the rarefaction arrives at a different time for the trough and the crest. This is called "feed-out" of the perturbation [5,6].…”

“…There are a number of hydrodynamic instability experiments on the laserirradiated surface (or x-ray irradiated surface). However, to date, the hydrodynamic phenomena related to the rarefaction wave have not been experimentally investigated in laser-irradiated targets, except for a few experimental studies in radiation drive targets [5]. Also, there is no direct measurement of the feed-out amplitude caused by rear surface perturbations.…”

Landau–Darrieus instability in an ablation front

“…2,[25][26][27][28] It is worth, however, to remark that there are also important differences between ablation and flame fronts. In addition, it may play a role during the initial phase of the target irradiation when the shock is still running into the shell and it is not yet accelerated.…”

The feedout process: Rayleigh–Taylor and Richtmyer–Meshkov instabilities in uniform, radiation-driven foils

“…Experiments involving feedout through a density discontinuity have been submitted for publication. 6 At early time, Fig. 2 shows radiation impinging on the smooth surface of the foil, causing surface ablation and a a͒ Also at the University of Wisconsin-Madison, Madison, Wisconsin; electronic mail: dps@lanl.gov subsequent shock propagating through the foil.…”