R. J. Fortner

Radiochemical Determination of Inertial Confinement Fusion Capsule Compression at the National Ignition Facility

We describe a radiochemical measurement of the ratio of isotope concentrations produced in a gold hohlraum surrounding an Inertial Confinement Fusion capsule at the National Ignition Facility (NIF). We relate the ratio of the concentrations of (n,γ) and (n,2n) products in the gold hohlraum matrix to the down-scatter of neutrons in the compressed fuel and, consequently, to the fuels areal density. The observed ratio of the concentrations of (198m+g)Au and (196g)Au is a performance signature of ablator areal density and the fuel assembly confinement time. We identify the measurement of nuclear cross sections of astrophysical importance as a potential application of the neutrons generated at the NIF.

Time and space resolved vacuum‐ultraviolet spectroscopy of an argon gas‐puff Z pinch

Time and radially resolved vacuum‐ultraviolet spectra from an argon gas‐puff Z pinch have been obtained using a grazing incidence spectrometer with gated microchannel plates curved to the Rowland circle. Most of the 50–300‐A radiation is emitted from a dense core (r≊0.4 mm, ne≳1019 cm−3, Te≊150 eV) which forms when the plasma assembles on the axis.

Prompt radiochemistry at the National Ignition Facility (invited).

Understanding mix in inertial confinement fusion (ICF) experiments at the National Ignition Facility requires the diagnosis of charged-particle reactions within an imploded target. Radiochemical diagnostics of these reactions are currently under study by scientists at Los Alamos and Lawrence Livermore National Laboratories. Measurement of these reactions requires assay of activated debris and tracer gases from the target. Presented below is an overview of the prompt radiochemistry diagnostic development efforts, including a discussion of the reactions of interest as well as the progress being made to collect and count activated material.

Spectroscopic studies of an argon plasma produced in a relativistic electron beam gas puff Z pinch

The spectra of argon ions emitted from a plasma created by discharging a 3‐TW relativistic electron beam generator through an argon gas column are reported. New lines have been classified for 2s 2pn–2pn+1 transition arrays in Ar XI–XV and energy levels have been derived for lithiumlike argon XVI. The effects of mass motion Doppler shifts on the spectra have been measured and systematic shifts of transition energies with charge state are observed in the data.

Soft-x-ray spectra of krypton xxiv–xxvii in gas puff Z-pinch plasmas

The spectra of krypton ions produced by the magnetic implosion of a krypton gas cylinder in the wavelength range from 10 to 250 A have been observed. Lines from highly ionized krypton ions from Kr xxiv to Kr xxvii have been identified by isoelectronic sequence extrapolation and compared with ab initio relativistic calculations. Energy levels are derived for Kr xxvi.

Experimental observations of density-sensitive line emission from neon-like ions in a laser-produced plasma

The authors have used dot spectroscopy to observe the line emission from a laser-produced plasma which contained sodium, chlorine and bromine. The K-shell emission from chlorine and sodium was used to determine the plasma electron temperature and density. The ratios of the X-ray resonance lines from neon-like bromine were found to be density sensitive. The bromine line ratios and electron densities predicted by a neon-like model agree reasonably well with the experimental results.

Direct observation of multiple L-shell vacancy effects in energetic heavy ion collisions☆

Abstract Observations have been made of soft L X-ray spectra resulting from collisions of 8–20 MeV oxygen ions and Ni, Cu and Zn atoms. These observations provide confirmation of the multiple L-shell vacancies proposed to explain recent experimental determinations of K-shell X-ray energy shifts in such collisions. The energy dependence of the single vacancy shifts indicate that the probability of outer shell ionization is a decreasing function of ion energy in this energy range.

A Small Bragg Diffraction X‐Ray Spectrometer

A small, easily constructed, and high efficiency Bragg angle x‐ray spectrometer has been developed. Employing either a lead stearate or a KAP crystal, it has been used to measure x rays in the 150–1000 eV region from ion‐atom collisions. At the carbon‐K energy (277 eV), it has an FWHM of 14 eV and an efficiency of 10−2 counts per incident x ray. Electronics and controls for fully automatic scans are described.

Note: Radiochemical measurement of fuel and ablator areal densities in cryogenic implosions at the National Ignition Facility

A new radiochemical method for determining deuterium-tritium (DT) fuel and plastic ablator (CH) areal densities (ρR) in high-convergence, cryogenic inertial confinement fusion implosions at the National Ignition Facility is described. It is based on measuring the (198)Au/(196)Au activation ratio using the collected post-shot debris of the Au hohlraum. The Au ratio combined with the independently measured neutron down scatter ratio uniquely determines the areal densities ρR(DT) and ρR(CH) during burn in the context of a simple 1-dimensional capsule model. The results show larger than expected ρR(CH) values, hinting at the presence of cold fuel-ablator mix.

Absolute Auger Yield Measurements of P+, O+, N+, C+, and B+ Projectiles Following Foil Excitation

Absolute K-and L-shell vacancy fractions of 50 to 500 keV P+-, O+-, N+-, C+-, and B+-ions excited by thin carbon foils have been measured using the technique of Auger-electron spectroscopy. The fraction of inner-shell vacancies in the excited projectile ions is proportional to the absolute Auger yield for low Z atoms. The projectile energy dependence of the vacancy fractions is duscussed.