Suppression of Rayleigh–Taylor instability due to radiative ablation in brominated plastic targets

Abstract

Suppression of hydrodynamic instabilities is very crucial for the ultimate goal of inertial fusion energy (IFE). A high-Z doped plastic of CHBr (brominated polystyrene) ablator is a very promising candidate to suppress the ablative Rayleigh–Taylor (RT) instability in a directly laser-driven IFE target. When a CHBr target is irradiated by intense laser beams, bromine atoms in the corona plasma emit strong radiation. The strong radiation drives the radiative ablation front inside the CHBr targets. This radiative ablation in the high-Z doped plastic target has many advantages for the suppression of the growth of the RT instability in analogy to the indirect-drive approach, i.e., large mass ablation rate, long density scale length and low peak density. Two-dimensional (2D) hydrodynamic simulation shows significant suppression of the RT instability in a CHBr target compared to an undoped polystyrene (CH) target. RT growth rate, calculated theoretically using the Betti–Goncharov procedure with a one-dimensional radiation-hydrodynamic simulation code, is in good agreement with the 2D calculations. Experiments were performed at the GEKKO XII– [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)] HIPER (High Intensity Plasma Experimental Research) laser facility. The trajectory of a laser-driven CHBr target observed in the experiment was reproduced fairly well by the simulation. The radiative ablation front formed inside a directly laser-driven CHBr target was clearly observed for the first time. The strong suppression of the RT instability in the CHBr target was confirmed using the face-on and side-on x-ray backlighting technique. The high-Z doped ablator can be applied to high density cryogenic deuterium–deuterium and deuterium–tritium compression, because the hydrogen-isotopes are nearly transparent to x rays, which are transmitted through the ablator from the laser-irradiation side.

Destabilizing effect of density gradient on the Kelvin–Helmholtz instability

“…The density gradient occurs naturally in these calculations and experiments, 8,9 and it is well known that the density gradient has the effect of reducing the linear growth rate of the RT instability, 10,11 particularly at short wavelengths. The effect of density gradient on the KH instability is still not well understood, which plays an important role in the performance of astrophysical jets and jetlike spikes in the nonlinear RM and RT instabilities.…”

Interface width effect on the classical Rayleigh–Taylor instability in the weakly nonlinear regime

“…The interface width effects ͑i.e., the density gradient effects or the density transition layer effects͒ occur naturally in these calculations and experiments. [14][15][16][17] The linear analyses of a multiple layer system of constant density fluids were carried out by Mikaelian 18-20 and Yang. 21 The linear growth rates of the RTI with continuous density profile were investigated by Mikaelian 22,23 and Munro,24 and the corresponding analytical formulas were obtained.…”

Temporal resolved x-ray penumbral imaging technique using heuristic image reconstruction procedure and wide dynamic range x-ray streak camera

“…[8][9][10] Details of these experimental results were reported in Ref. 10. We also measured the density profile of laser-produced tin plasmas using this technique.…”