Joseph Cowan

TRIDENT high-energy-density facility experimental capabilities and diagnostics

The newly upgraded TRIDENT high-energy-density (HED) facility provides high-energy short-pulse laser-matter interactions with powers in excess of 200 TW and energies greater than 120 J. In addition, TRIDENT retains two long-pulse (nanoseconds to microseconds) beams that are available for simultaneous use in either the same experiment or a separate one. The facilitys flexibility is enhanced by the presence of two separate target chambers with a third undergoing commissioning. This capability allows the experimental configuration to be optimized by choosing the chamber with the most advantageous geometry and features. The TRIDENT facility also provides a wide range of standard instruments including optical, x-ray, and particle diagnostics. In addition, one chamber has a 10 in. manipulator allowing OMEGA and National Ignition Facility (NIF) diagnostics to be prototyped and calibrated.

Characterization and cross calibration of Agfa D4, D7, and D8 and Kodak SR45 x-ray films against direct exposure film at 4.0–5.5keV

Kodak direct exposure film (DEF) [B. L. Henke et al., J. Opt. Soc. Am. B 3, 1540 (1986)] has been the standard for moderate energy (1–10keV) x-ray diagnostic applications among the high-energy-density and inertial confinement fusion research communities. However, market forces have prompted Kodak to discontinue production of DEF, leaving these specialized communities searching for a replacement. We have conducted cross-calibration experiments and film characterizations on five possible substitutes for Kodak DEF. The film types studied were Kodak’s Biomax MR (BMR) and SR45 along with Agfa’s D8, D7, and D4sc. None of the films tested matched the speed of DEF. BMR and D8 were closest but D8 exhibited lower noise, with superior resolution and dynamic range. Agfa D7, Agfa D4sc, and Kodak SR45 were significantly less sensitive than BMR and D8, however, the improvements they yielded in resolution and dynamic range warrant their use if experimental constraints allow.

Characterization of radiochromic film scanning techniques used in short-pulse-laser ion acceleration

Radiochromic film (RCF) is increasingly being used as a detector for proton beams from short-pulse laser-matter interaction experiments using the RCF imaging spectroscope technique. The community has traditionally used inexpensive flatbed scanners to digitize and analyze the data, as opposed to more expensive and time-consuming microdensitometers (MicroDs). Often, the RCF densities in some regions exceed an optical density (OD) of 3. Flatbed scanners are generally limited to a maximum OD of approximately 3. Because of the high exposure density, flatbed scanners may yield data that are not reliable due to light scatter and light diffusion from areas of low density to areas of high density. This happens even when the OD is slightly above 1. We will demonstrate the limitations of using flatbed scanners for this type of radiographic media and characterize them compared to measurements made using a MicroD. A technique for cross characterizing both systems using a diffuse densitometer with a NIST wedge will also be presented.

Quantifying equation-of-state and opacity errors using integrated supersonic diffusive radiation flow experiments on the National Ignition Facility

A well diagnosed campaign of supersonic, diffusive radiation flow experiments has been fielded on the National Ignition Facility. These experiments have used the accurate measurements of delivered laser energy and foam density to enable an investigation into SESAMEs tabulated equation-of-state values and CASSANDRAs predicted opacity values for the low-density C8H7Cl foam used throughout the campaign. We report that the results from initial simulations under-predicted the arrival time of the radiation wave through the foam by ≈22%. A simulation study was conducted that artificially scaled the equation-of-state and opacity with the intended aim of quantifying the systematic offsets in both CASSANDRA and SESAME. Two separate hypotheses which describe these errors have been tested using the entire ensemble of data, with one being supported by these data.

A soft x-ray transmission grating imaging-spectrometer for the National Ignition Facility

A soft x-ray transmission grating spectrometer has been designed for use on high energy-density physics experiments at the National Ignition Facility (NIF); coupled to one of the NIF gated x-ray detectors it records 16 time-gated spectra between 250 and 1000 eV with 100 ps temporal resolution. The trade-off between spectral and spatial resolution leads to an optimized design for measurement of emission around the peak of a 100-300 eV blackbody spectrum. Performance qualification results from the NIF, the Trident Laser Facility and vacuum ultraviolet beamline at the National Synchrotron Light Source, evidence a <100 μm spatial resolution in combination with a source-size limited spectral resolution that is <10 eV at photon energies of 300 eV.

Overcritical to Underdense Plasma in Under 1

When a high-intensity laser interacts with a solid target, a well-known phenomenon, namely, the production of multimegaelectronvolt particles, occurs. However, if the laser and target thickness are carefully chosen to coincide with the burn-through of the lasers amplified-spontaneous-emission prepulse, the main pulse of the laser can interact with a short-scale-length near-critical-density plasma, and a very low divergent electron beam can be produced.

\mu \hbox{m}

Abstract The measurement of the density of materials, especially ultralow-density foams, is difficult in that the measurement must be precise and localizable. The density of the material is often governed by its cellular (i.e., porous) structure, and many techniques exist to create that structure. Often, the cellular structure can vary from one location within the material to another, and when at low densities (i.e., densities lower than ~500 mg/cm3), it can vary due to shrinkage during syneresis, collapse under the weight of gravity, or gas/water vapor uptake. Quantifying this variation is important for a variety of applications, especially when used in plasma physics targets. Knowing the density and its variation across the sample is critical for experimental results to be accurately predicted by physics calculations and for modeling the results of the physics targets. The use of quasi-monochromatic radiography provides a means to image the two-dimensional (2-D) distribution of density variation within silica aerogel materials and to quantitatively measure that variation from sample to sample and lot to lot. For this study, two batches of silica aerogels with targeted densities of ~20 mg/cm3 were created, one batch at Lawrence Livermore National Laboratory, and the other batch at Los Alamos National Laboratory. Outlined here is a quasi-monochromatic radiography system using various X-ray sources coupled to a doubly curved crystal optic and X-ray charge-coupled device camera to image and characterize these materials. It was found that measuring the density both gravimetrically and using quasi-monochromatic radiography were statistically identical, although the two batches were found to be slightly higher than their targeted density due to shrinkage. The radiography system also provided 2-D information as to the aerogel quality, i.e., presence of voids, chipped material, or inclusions.

: 150 TW Laser–Thin-Target Interactions for Particle Acceleration

We will discuss our attempts to measure of the absolute gain and its variation across the face of fast gated multichannel plate [MCP] detectors for 4.75 keV x-rays. We found that some of the gated strips had variations in the gain along and perpendicular to the direction of travel, and significant variation along the time axis that requires these calibrations to obtain the correct time history of gated events. We will also present some of the results on the linearity of such gain with input x-ray signal amplitude.