First experiments on Revolver shell collisions at the OMEGA laser

Abstract

Results of recent experiments on the OMEGA Laser are presented, demonstrating the ablator-driver shell collision relevant to the outer two shells of the Revolver triple-shell inertial-confinement-fusion concept [K. Molvig et al., PRL 116, 255003 (2016)]. These nested two-shell experiments measured the pre-and postcollision outer-surface trajectory of the 7.19 g/cc chromium inner shell. Measurements of the shell trajectory are in excellent agreement with simulations; the measured outer-surface velocity was 7.52 ± 0.59 cm/µs compared to the simulated value of 7.27 cm/µs. Agreement between the measurements and simulations provides confidence in our ability to model collisions with features which have not been validated previously. Notable features include the absence of ∼40 mg/cc foam between shells commonly used in double shell experiments, a dense (7.19 g/cc) inner shell representative of the densities to be used at full scale, approximately mass matched ablator payload and inner shells, and the inclusion of a tamping-layer-like cushion layer for the express purpose of reducing the transfer of high mode growth to the driver shell and mediation of the shell collision. Agreement of experimental measurements with models improves our confidence in the models used to design the Revolver ignition target.

A two-layer single shell magnetized target for lessening the Nernst effect

“…Multi-shell targets, such as double-shell [10] and revolver [11][12][13], have recently gained attention in ICF as a potential concept seeking to achieve ignition at lower ignition temperatures than single-shell concepts. Double-shell capsules were explored using a laser indirect drive and resulted in a robust burn metric at the national ignition facility [14].…”

“…Alternative targets designed in recent years commonly have an inner layer of high-Z metal surrounding the fuel. High-Z materials have high albedos and can re-radiate most of the radiation coming from the hot fuel [13,21,22]. This reduces the required ignition temperature and the convergence ratio (C vg = R f0 R fs ), as well as the instability growth.…”

Simulations on the multi-shell target ignition driven by radiation pulse in Z-pinch dynamic hohlraum*

“…[5][6][7] For a hot-spot central ignition target, a proper pulse shape that can generate three or four shocks with precise timing and amplitudes is required to ignite the fuel with minimal energy. [8] For volumetric ignition targets, such as doubleshell targets [9][10][11][12][13] or multi-shell targets, [14][15][16][17][18] although much simpler pulse can be used, an appropriate shape is still needed when other considerations are taken into account. For example, Amendt [10] recommended an x-ray pulse with radiation temperature nearly constant in time to reduce the plasmamediated laser backscatter and minimize the fuel mixing in the double-shell target implosion on National Ignition Facility.…”