R. L. Holmes

Observation of mix in a compressible plasma in a convergent cylindrical geometry

Laser beams that directly drive a cylindrical implosion are used to create a measurable region of mixed material in a compressible plasma state, for the first time in a convergent geometry. The turbulence driven by the Richtmyer–Meshkov instability by shock passage across a density discontinuity mixes marker material that is radiographically opaque. The width of the mix layer is compared between a system with large surface roughness and an initially smooth system. The experiment is described and results are compared to multi-dimensional numerical simulation, including three-dimensional turbulence calculations. The calculations adequately match the observations provided the measured initial conditions are used.

Highly resolved measurements of defect evolution under heated-and-shocked conditions

One of the principal advantages of a double-shell capsule design is the potential for ignition without requiring cryogenic implosions. These designs compress deuterium fuel by transferring kinetic energy from a laser-ablated outer shell to an inner shell by means of a nearly elastic symmetric collision. However, prior to this collision the inner shell experiences varying levels of preheat such that any nonuniformities can evolve significantly. It is the condition of these perturbations at the time the collision-induced shock compresses the inner shell that ultimately dictates capsule performance. With this in mind, a series of experiments have been performed on the OMEGA laser facility [R. T. Boehly et al., Opt. Comm. 133, 495 (1997)] that produce highly resolved measurements of defect evolution under heated-and-shocked conditions. Tin L-shell radiation is used to heat a layered package of epoxy and foam. The epoxy can be engineered with a variety of surface perturbations or defects. As the system evolves...

IMPROVED EOS FOR DESCRIBING HIGH‐TEMPERATURE OFF‐HUGONIOT STATES IN EPOXY

Modelling of off‐Hugoniot states in an expanding interface subjected to a shock reveals the importance of a chemically complete description of the materials. Hydrodynamic experiments typically rely on pre‐shot target characterization to predict how initial perturbations will affect the late‐time hydrodynamic mixing. However, it is the condition of these perturbations at the time of shock arrival that dominates their eventual late‐time evolution. In some cases these perturbations are heated prior to the arrival of the main shock. Correctly modelling how temperature and density gradients will develop in the pre‐heated material requires an understanding of the equation‐of‐state. In the experiment modelled, an epoxy/foam layered package was subjected to tin L‐shell radiation, producing an expanding assembly at a well‐defined temperature. This assembly was then subjected to a controlled shock, and the evolution of the epoxy‐foam interface imaged with x‐ray radiography. Modelling of the data with the hydrodynam...

INERTIAL CONFINEMENT FUSION RESEARCH AT LOS ALAMOS NATIONAL LABORATORY

Inertial confinement fusion research at Los Alamos National Laboratory is focused on high‐leverage areas of thermonuclear ignition to which LANL can apply its historic strengths and that are complementary to high‐energy‐density‐physics topics. Using the Trident and Omega laser facilities, experiments are pursued in laser‐plasma instabilities, symmetry, Be technologies, neutron and fusion‐product diagnostics, and defect hydrodynamics.