Showing papers by "Roger Alan Vesey published in 2001"

Development and Characterization of a Z-Pinch Driven Hohlraum High-Yield Inertial Confinement Fusion Target Concept

Abstract: Initial experiments to study the Z-pinch-driven hohlraum high-yield inertial confinement fusion (ICF) concept of Hammer, Tabak, and Porter [Hammer et al., Phys. Plasmas 6, 2129 (1999)] are described. The relationship between measured pinch power, hohlraum temperature, and secondary hohlraum coupling (“hohlraum energetics”) is well understood from zero-dimensional semianalytic, and two-dimensional view factor and radiation magnetohydrodynamics models. These experiments have shown the highest x-ray powers coupled to any Z-pinch-driven secondary hohlraum (26±5 TW), indicating the concept could scale to fusion yields of >200 MJ. A novel, single-sided power feed, double-pinch driven secondary that meets the pinch simultaneity requirements for polar radiation symmetry has also been developed. This source will permit investigation of the pinch power balance and hohlraum geometry requirements for ICF relevant secondary radiation symmetry, leading to a capsule implosion capability on the Z accelerator [Spielman et al., Phys. Plasmas 5, 2105 (1998)].

Scaling and optimization of the radiation temperature in dynamic hohlraums

Abstract: A quasianalytic model of the dynamic hohlraum is presented. Results of the model are compared to both experiments and full numerical simulations with good agreement. The computational simplicity of the model allows one to find the behavior of the hohlraum radiation temperature as a function of the various parameters of the system and thus find optimum parameters as a function of the driving current. The model is used to investigate the benefits of ablative standoff and quasispherical Z pinches.

Zero-dimensional energetics scaling models for z-pinch-driven hohlraums

Abstract: Wire array z pinches on the Z accelerator provide the most intense laboratory source of soft X rays in the world. The unique combination of a near-Planckian radiation source with high X-ray production efficiency (10 to 15% wall plug), large X-ray powers and energies (>100 TW, ≥0.8 MJ in 6 ns to 7 ns), large characteristic hohlraum volumes (0.5 to >10cm 3 ), long pulse lengths (5 to 20 ns), and low capital cost ( 200 MJ yield) ICF capsules with adequate radiation symmetry and margin. The z-pinch-driven hohlraum approach of Hammer et al. (1999) may provide a conservative and robust solution to the requirements for high yield, and is currently being studied on the Z accelerator. This paper describes a multiple-region, 0-D hohlraum energetics model for z-pinch-driven hohlraums in four configurations. We observe consistency between the model and the measured X-ray powers and hohlraum wall temperatures to within ±20% in X-ray flux, for the four configurations. The scaling of pinch energy and radiation-driven anode-cathode gap closure with drive current are also examined.

Design and simulation of X-ray backlit targets for z-pinch hohlraum symmetry experiments

Abstract: Summary form only given, as follows. Capsule radiation symmetry is a crucial issue in the design of the z-pinch driven hohlraum approach to high-yield inertial confinement fusion. Capsule symmetry may be influenced by the power imbalance of the two z-pinch X-ray sources, and by hohlraum effects (geometry, time-dependent albedo, wall motion). 2-D and 3-D radiosity ("viewfactor") models have been used to design hohlraums that optimize the capsule radiation symmetry for experiments on Z as well as for high-yield targets. The goals of capsule symmetry experiments on Z include commissioning the Z-beamlet backlighter laser and requisite initial imaging detectors, measuring capsule flux asymmetry at the several percent level, and demonstrating understanding of the factors influencing capsule asymmetry in z-pinch hohlraums. Design and simulation efforts have focused on: (a) hohlraum radiation transport models to determine the sensitivity of capsule flux asymmetry to hohlraum geometry, top-bottom pinch power imbalance, and pinch mistiming, (a) 2-mm diameter, 60-/spl mu/m thick plastic shells designed to implode within 10 ns after the secondary hohlraum reaches its peak drive temperature of 75-85 eV, providing a suitable target for initial experiments at lower backlighting energies (2.5-3 keV), (b) 3- to 5-mm diameter thin (20-40 /spl mu/m) Ge-doped plastic shells designed for backlighting with Ti K-shell X-rays to assess symmetry early in the capsule implosion, and (c) uniform density foam spheres (/spl sim/50-100 mg/cc) also designed for Ti backlighting to image the trajectory of the shock/ablation front feature throughout the drive pulse. We present the results of postprocessed 1- and 2-D radiation-hydrodynamics calculations for each type of symmetry target, describing their advantages and disadvantages, and show comparisons with preliminary experimental data.