A. R. Moats

Target diagnostic system for the national ignition facility (invited)

A review of recent progress on the design of a diagnostic system proposed for ignition target experiments on the National Ignition Facility (NIF) will be presented. This diagnostic package contains an extensive suite of optical, x ray, gamma ray, and neutron diagnostics that enable measurements of the performance of both direct and indirect driven NIF targets. The philosophy used in designing all of the diagnostics in the set has emphasized redundant and independent measurement of fundamental physical quantities relevant to the operation of the NIF target. A unique feature of these diagnostics is that they are being designed to be capable of operating in the high radiation, electromagnetic pulse, and debris backgrounds expected on the NIF facility. The diagnostic system proposed can be categorized into three broad areas: laser characterization, hohlraum characterization, and capsule performance diagnostics. The operating principles of a representative instrument from each class of diagnostic employed in t...

ICF target diagnostics on PBFA II (invited)

Particle Beam Fusion Accelerator II is a light‐ion fusion accelerator that is presently capable of irradiating a 6‐mm‐diam sphere with ∼50 kJ of 5.5‐MeV protons in ∼15 ns. An array of particle and x‐ray diagnostics fielded on proton Inertial Confinement Fusion target experiments quantifies the incident particle beam and the subsequent target response. An overview of the ion and target diagnostic setup and capabilities will be given in the context of recent proton beam experiments aimed at studying soft x‐ray emission from foam‐filled targets and the hydrodynamic response of exploding‐pusher targets. Ion beam diagnostics indicate ∼100 kJ of proton beam energy incident within a 1.2‐cm radius of the center of the diode with an azimuthal uniformity which varied between 6% and 29%. Foam‐filled target temperatures of 35 eV and closure velocities of 4 cm/μs were measured.

Time-dependent, x-ray spectral unfolds and brightness temperatures for intense Li+ ion beam-driven hohlraums

X-ray-producing hohlraums are being studied as indirect drives for Inertial Confinement Fusion targets. In a 1994 target series on the PBFAII accelerator, cylindrical hohlraum targets were heated by an intense Li{sup +} ion beam and viewed by an array of 13 time-resolved, filtered x-ray detectors (XRDs). The UFO unfold code and its suite of auxiliary functions were used extensively in obtaining time- resolved x-ray spectra and radiation temperatures from this diagnostic. UFO was also used to obtain fitted response functions from calibration data, to simulate data from blackbody x-ray spectra of interest, to determine the suitability of various unfolding parameters (e.g., energy domain, energy partition, smoothing conditions, and basis functions), to interpolate the XRD signal traces, and to unfold experimental data. The simulation capabilities of the code were useful in understanding an anomalous feature in the unfolded spectra at low photon energies ({le} 100 eV). Uncertainties in the differential and energy-integrated unfolded spectra were estimated from uncertainties in the data. The time-history of the radiation temperature agreed well with independent calculations of the wall temperature in the hohlraum.

Lithium beam‐driven target experiments at 1015 W/g on PBFA II at Sandia National Laboratories

A lithium beam is focused to an intensity 1–2 TW/cm2. The beam divergencies have been measured as low as 23 mrad. This lithium beam has the specific power deposition of ∼10 W/g, the beam‐driven target experiments have achieved radiation temperature of 58 eV.(AIP)

PBFA II lithium beam characterization from inner‐shell x‐ray images

The Particle Beam Fusion Accelerator (PBFA II) is now driving targets with ICF‐relevant lithium ion beams. During the most recent lithium beam target series, time‐integrated x‐ray pinhole cameras viewed the ion‐induced inner‐shell x‐ray fluorescence from the central gold cone target and a titanium‐coated strip. Ion‐beam profiles at a nominal 10‐mm radius and fixed azimuthal direction were obtained from images of the Ti Kα fluorescence of a Ti‐coated Al diagnostic wire. The gold cone gave us beam profiles at a nominal 3‐mm radius and at all azimuthal angles from the Au Lα fluorescence. From these profiles, we obtained the ion‐beam vertical focus position, the full width at half maximum, and the degree of azimuthal uniformity for the lithium target shots. For these initial results, beam steering problems were evident. Azimuthal uniformity was measured from the ion‐beam footprint on the outer Au case (predominantly Au Lα) of the hohlraum target and was found to be in the same range (up to 30%) as for previou...

Measurement of beam properties and reproducibility on recent PBFA II target shots

Recent proton experiments on Particle Beam Fusion Accelerator II used a 2 μm gold foil cone to characterize the ion beam. Using the ion beam images obtained by viewing beam‐induced characteristic line radiation emitted by such foils with time‐integrated x‐ray pinhole cameras, the beam centroid axial location and azimuthal symmetry have been analyzed for a recent series of target shots. Azimuthal symmetry on the target midplane on individual shots varied from 6% to 29%. Averaged over the entire series of shots, inferred intensities on the target midplane varied by 24% to 37% from quadrant to quadrant. The beam profiles and beam reproducibility are vital to the interpretation of the results of these target experiments.

Ion contamination of x-ray pinhole camera images on PBFA II

Inner‐shell x‐ray pinhole cameras are an important diagnostic for time‐averaged beam profile measurements on PBFA‐II experiments which requires no shielding from the diode magnetic field. However, the same ions that create the inner‐shell x rays can also Rutherford scatter and directly expose the x‐ray film. A double image, due to this effect, has been observed in PBFA‐II data. In this paper, we derive the expected film density due to these scattered ions relative to the film density from the ion‐induced x‐ray line radiation from titanium, aluminum, and gold targets. We then show that our calculated degree of ion contamination for a gold target Mα camera recently fielded on PBFA‐II is consistent with the actual images observed−a phantom image tentatively identified as proton contamination with a film density of the same order of magnitude as the x‐ray image. The amount of ion contamination is strongly dependent on the optical filtering used. For less heavily filtered cameras, we will show that this contam...

Light ion beam ICF program overview

The light ion fusion program at Sandia National Laboratories is reviewed. The program is based on the indirect‐drive target concept and has the long‐term objective to obtain high yield in a microfusion facility. The near‐term technical effort will focus on increasing intensity and demonstrating 100 eV temperature in an ion hohlraum. Some concepts were tested experimentally confirming the accessibility of anticipated goals. (AIP)

Light ion hohlraum target experiments on PBFA II and Nova

The goal of the National Inertial Confinement Fusion (ICF) Program in the United States is a target yield in the range of 200 to 1000 MJ. To address this goal, the near‐term emphasis in the Light Ion Target Physics program is to design a credible high‐gain target driven by ion beams. Based on this target design, we have identified ion beam spatial parameters, ion beam energy and power deposition, the conversion of ion‐beam energy into soft x‐ray thermal radiation, the conversion of ion‐beam energy into hydrodynamic motion, radiation smoothing in low‐density foams, and internal pulse shaping as the critical physics issues. These issues are currently being addressed in both ion‐ and laser‐driven experiments.

A pulsed-laser X-ray source for X-ray diagnostic calibration

Summary form only given. We are now performing imploding annular wire-array experiments on the PBFA-Z accelerator. The experimental diagnostics include X-ray diode detectors (XRDs), photoconducting diode detectors (PCDs), and X-ray pinhole cameras both time-integrating and time-dependent. We have set up a pulsed-laser x-ray source for calibration of these diagnostics. A pulsed 10-joule Nd:YAG laser is shot onto a low-Z target, and a combination of filters then provides a large-area, mono-energetic source with a one-nanosecond pulse width. Measurements of the diagnostics sensitivity between 160 eV and 3 keV can be determined with this source with the appropriate combination of target and filter. The reference standard is a 1024/spl times/1024 pixel X-ray CCD that measures the source intensity and is calibrated at 100 eV to 2500 eV.