[en] Results from a series of shock trajectory measurements in planar liquid deuterium targets will set the pulse shape they use for ignition capsules at the National Ignition Facility. They discuss outstanding issues for this concept, in particular, ideas for certifying that the drive on a planar sample is the same as on a spherical capsule

[en] Phase-shifting interferometry reveals that a heat flux normal to the gas-solid interface reduces the surface roughness of thick (10--300 μm) multicrystalline D₂ films. The initial roughness, caused by misaligned crystals and grain boundaries produced during the initial random nucleation and rapid crystal growth used in the experiment decreases with increasing heat flux. A simple energy minimization model quantitatively explains the functional relationship between surface roughness and heat flux

[en] Here, the canonical high pressure equation of state measurement is to induce a shock wave in the sample material and measure two mechanical properties of the shocked material or shock wave. For accurate measurements, the experiment is normally designed to generate a planar shock which is as steady as possible in space and time, and a single state is measured. A converging shock strengthens as it propagates, so a range of shock pressures is induced in a single experiment. However, equation of state measurements must then account for spatial and temporal gradients. We have used x-ray radiography of spherically convergingmore » shocks to determine states along the shock Hugoniot. The radius-time history of the shock, and thus its speed, was measured by radiographing the position of the shock front as a function of time using an x-ray streak camera. The density profile of the shock was then inferred from the x-ray transmission at each instant of time. Simultaneous measurement of the density at the shock front and the shock speed determines an absolute mechanical Hugoniot state. The density profile was reconstructed using the known, unshocked density which strongly constrains the density jump at the shock front. The radiographic configuration and streak camera behavior were treated in detail to reduce systematic errors. Measurements were performed on the Omega and National Ignition Facility lasers, using a hohlraum to induce a spatially uniform drive over the outside of a solid, spherical sample and a laser-heated thermal plasma as an x-ray source for radiography. Absolute shock Hugoniot measurements were demonstrated for carbon-containing samples of different composition and initial density, up to temperatures at which K-shell ionization reduced the opacity behind the shock. Here we present the experimental method using measurements of polystyrene as an example.

[en] The expected value of nuclear spin polarization to inertial confinement fusion is recapitulated. A comparison of brute force versus dynamic nuclear polarization, as applied to solid deuterium-tritium, is given, and the need for a long triton polarization memory time (longitudinal nuclear relaxation time) is shown. The time constant for 25 mol%T₂-50 DT-25 D₂ is a short 0.3 s at 5/degree/K and waiting lowers it to 0.1 s. Use of 90 to 96 mol% molecular DT raises the time constant to 0.9 s and addition of about 20 mol% nH₂ increases it to 5 to 7 s. The theory shows that the species shortening the triton memory time is the J = 1 T₂, which can be reduced in our samples only by self-catalysis. The heating in order to mix in nH₂ increases the percent of J = 1 T₂ and mixing may not be perfect. The experiments have increased the triton memory time twenty-fold and shown that removal of the J = 1 T₂ is the key to improved results

[en] Simultaneous measurements of shock velocity and optical reflectance at 1064, 808, and 404 nm of a high pressure shock front propagating through liquid deuterium show a continuous increase in reflectance from below 10% and saturating at ∼(40-60)% in the range of shock velocities from 12 to 20 μm/ns (pressure range 17-50 GPa). The high optical reflectance is evidence that the shocked deuterium reaches a conducting state characteristic of a metallic fluid. Above 20 μm/ns shock velocity (50 GPa pressure) reflectance is constant indicating that the transformation is substantially complete. (c) 2000 The American Physical Society

[en] A high-intensity laser was used to shock compress liquid deuterium to pressures between 0.22 and 3.4 megabars (Mbar). Shock density, pressure, and temperature were determined using a variety of experimental techniques and diagnostics. This pressure regime spans the transformation of deuterium from an insulating molecular fluid to an atomic metallic fluid. Data reveal a significant increase in compressibility and a temperature inflection near 1 Mbar, both indicative of such a transition. Single-wavelength reflectivity measurements of the shock front demonstrated that deuterium shocked above ∼0.5 Mbar is indeed metallic. (c) 2000 The American Astronomical Society

[en] We have developed and tested several optical interferometric diagnostics to measure preheat and shock velocity in high-pressure equation of state experiments on the Nova laser. Theory and practical application of interferometric measurement techniques with illustrative experimental results are presented

[en] We present experimental work exploring displacement and velocity interferometry as high spatial and temporal resolution diagnostics for measuring target preheat and the speed, planarity, and steadiness of a shock wave. A chirped pulse reflectometry experiment is also proposed as a frequency domain alternative for shock speed measurements. These techniques fill a need for high-precision diagnostics to derive accurate laboratory-based equation-of-state data at shock wave-driven pressures directly relevant to astrophysical systems. The performance of these optical laser probe techniques may exceed conventional passive techniques such as temporally streaked recording of optical emission upon shock breakout or side-on streaked X-ray radiography. Results from Nova laser and high-intensity ultrashort pulse experiments are presented. (c) 2000 The American Astronomical Society

[en] Pyrometric measurements of single-shock-compressed liquid deuterium reveal that shock front temperatures T increase from 0.47 to 4.4eV as the pressure P increases from 31 to 230GPa. Where deuterium becomes both conducting and highly compressible, 30≤P le 50 GPa , T is lower than most models predict and T<< T_Fermi , proving that deuterium is a degenerate Fermi-liquid metal. At P>50 Gpa , where the optical reflectivity is saturated, there is an increase in the rate that T increases with P

[en] Velocity interferometers are typically used to measure velocities of surfaces at a single point or along an imaged line as a function of time. We describe an optical arrangement that enables high-resolution measurements of the two-dimensional velocity field across a shock front or shocked interface. The technique is employed to measure microscopic fluctuations in shock fronts that have passed through materials being considered as ablators for indirect-drive inertial confinement fusion. With picosecond time resolution the instrument captures velocity modes with wavelengths as short as 2.5 μm at a resolution of ∼10 m/s rms on velocity fields averaging many km/s over an 800 μm field of view.