Perturbation evolution started by Richtmyer-Meshkov instability in planar laser targets

Abstract

The first observations of the interaction of the Richtmyer-Meshkov (RM) instability with reflected shock and rarefaction waves in laser-driven targets are reported.The RM growth is started by a shock wave incident upon a rippled interface between low-density foam and solid plastic. Subsequent interaction of secondary rarefaction and/or shock waves arriving from the ablation front and the rear surface of the target with the RM-unstable interface stops the perturbation growth and reverses its direction. The ensuing exponential Rayleigh-Taylor growth thus can sometimes proceed with an inverted phase.

Classical and ablative Richtmyer–Meshkov instability and other ICF-relevant plasma flows diagnosed with monochromatic x-ray imaging

“…Until very recently, little experimental data were available for testing the codes in the RT-seeding relevant regimes. The situation changed with the development of new diagnostic techniques [8][9][10][11]40]. Some examples are presented below in this section.…”

“…The setup provides spatial resolution in one relevant direction, i.e. along the wave vector of the ripple on the target surface, producing 1D streak records [8][9][10].…”

“…Our experiments [10] were made with planar targets that featured a single-mode, twodimensional (2D) rippled interface separating low-density resorcinol formaldehyde foam from solid plastic. Typical parameters of our targets were: foam density pulse with a foot: ) (t m δ passes through zero and, as long as the laser pulse is on, continues to grow in the negative direction, accumulating more mass where there was less of it initially.…”

“…However, measurements of mass perturbation evolution due to Richtmyer-Meshkov (RM) instability (ripples on the front surface) or feedout (ripples on the back side) related oscillations present new challenge to imaging diagnostics because of essentially non-monotonic evolution of the processes under study [8][9][10]. To extend the capabilities of our diagnostic technique we added a streak camera to the system, which made it possible to analyze continuous time behavior of an x-ray image.…”

“…The most advanced modeling is still limited in resolution and relies upon both physical and numerical assumptions and simplifications whose adequacy needs to be constantly tested. For this reason, experimental verification of the codes and validation of the underlying physical models in the ICF-relevant physical conditions has been an area of active study in all the major centers of laser fusion research for the last decades, see [7][8][9][10][11][12][13][14][15] and references therein.…”