Nonthermal excitation of atomic states by suprathermal electrons was observed for the first time within inertial confinement fusion hohlraum plasmas. The nonthermal excitation process results in the simultaneous emission of the Ly-alpha transition and the K-shell satellite series (lithiumlike through carbonlike) which were observed on temporally resolved x-ray emission spectra. A quantitative analysis with a time-dependent collisional-radiative non-Maxwellian model shows that these spectra can be used to obtain temporally and spatially resolved measurements of the suprathermal electron fraction in indirectly driven inertial confinement fusion targets.

In this study we use spectroscopy and x-ray imaging to investigate the macroscopic plasma flow in mm-sized laser-produced hohlraum plasmas. By using multiple diagnostics to triangulate the emission on a single experiment, we can pinpoint the position of dopants placed inside the hohlraum. X-ray emission from the foil has been used in the past to measure electron temperature. Here we analyze the spatial movement of dopant plasmas for comparison to hydrodynamic calculations.

A simple strategy is presented to create moderately coupled plasmas: it consists in a colliding foil system irradiated by two laser beams. In these correlated plasmas, signatures of transient molecular behaviour are shown. Two studies are intensively developed here: the simulation of the experiment and the X-ray spectroscopic and imaging diagnostics. A reciprocal action between the two studies allows an optimization of both the compression and the associated dense plasma effects. We present accurate fluorine Lyβ spectra as an appropriate example for the exhibition of the non-spherical symmetry of the bound electronic structure.

The characterization of laser‐produced plasmas has required the application of spectroscopic techniques to non‐standard conditions where kinetics models have not been extensively tested. The plasmas are produced by the Nova laser for the study of inertial confinement fusion, can be mm in size, and evolve on sub‐nanosecond time scales. These targets typically achieve electron temperatures from 2–4 keV and electron densities of 1020–1022 cm−3. We have measured the electron temperature of two types of targets: bags of gas and hohlraums, Au cylinders with laser entrance holes in the flat ends. By comparing data from different targets, we examine the time‐dependence of spectroscopic plasma diagnostics.

In order to prevent high‐Z plasma from filling in the hohlraum in indirect drive experiments, a low‐Z material, or tamper is introduced into the hohlraum. This material, when fully ionized is typically less than one‐tenth of the critical density for the laser light used to illuminate the hohlraum. This tamper absorbs little of the laser light, thus allowing most of the laser energy to be absorbed in the high‐Z material. However, the pressure associated with this tamper is sufficient to keep the hohlraum wall material from moving a significant distance into the interior of the hohlraum. In this paper we discuss measurements of the motion of the interface between the tamper and the high‐Z hohlraum material. We also present measurements of the effect the tamper has on the hohlraum temperature.

Understanding drive symmetry in gas-filled hohlraums is currently of interest because the baseline design of the indirect drive ignition target for the planned National Ignition Facility uses a gas-filled hohlraum. This paper reports on the results of a series of experiments performed at the Nova laser [C. Bibeau et al. Appl. Opt. 31, 5799 (1992)] facility at Lawrence Livermore National Laboratory with the goal of understanding time-dependent drive symmetry in gas filled hohlraums. Time-dependent symmetry data from capsule implosions and reemission targets in gas-filled hohlraums are discussed. Results of symmetry measurements using thin wall gas-filled hohlraums are also discussed. The results show that the gas is effective in impeding the motion of the wall blowoff material, and that the resulting implosion performance of the capsule is not significantly degraded from vacuum results. The implosion symmetry in gas differs from vacuum results with similar laser pointing indicating a shift in beam position on the hohlraum wall and hotter drive at the capsule’s poles than at the equator. A theory has been proposed to explain the observed shift as a plasma physics effect: beam steering due to filamentation and transverse plasma flows.

The intensity dependent deflection of a laser beam traversing an exploding foil plasma is measured for the first time. An incident {ital f}/8 probe beam exhibits deflection of up to 6{degree} and angular spreading of as much as a 17{degree} cone angle ({ital f}/3.3) as it exits a preformed plasma with significant plasma flow. {copyright} {ital 1996 The American Physical Society.}

We report on the use of x-ray spectroscopy of mid-Z dopants to measure the electron temperature of hohlraum targets. The hohlraums are gas-filled Au cylinders and, when irradiated with 20 kJ of 0.35 mu m laser light, they become mm-sized plasmas bathed in a radiation field. The peak temperatures achieved by the target are 3.7 keV. In addition to being the first electron temperature measurements of the hohlraum itself, these measurements enable an investigation of the thermal energy and electron conduction of the target.

We have successfully employed isoelectronic line ratios to measure the electron temperature in gas-filled Hohlraum targets and gas bags shot with the Nova laser. These targets produce millimeter-scale-length plasmas with electron density ${\mathit{N}}_{\mathit{e}}$\ensuremath{\sim}${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ and electron temperature ${\mathit{T}}_{\mathit{e}}$\ensuremath{\sim}3 keV. The Hohlraum targets can also produce radiation temperature exceeding 200 eV. Isoelectronic line ratios are well suited to this measurement because they are relatively insensitive to radiation field effects in Hohlraum targets, opacity, transients, and variations in electron density compared to conventional line ratios. We survey the properties of isoelectronic line ratios formed from ratios of n-to-1 resonance transitions in heliumlike Cr to the same transitions in Ti and compare with conventional ratios of n-to-1 transitions in hydrogenlike Ti to the corresponding transitions in heliumlike Ti, concentrating on plasma parameter ranges of interest to the Nova experiments. We also consider the same ratios using K and Cl. Atomic kinetics are treated using collisional-radiative models and experimental data are analyzed with the aid of radiation-hydrodynamics calculations. When we apply isoelectronic techniques to the Nova experimental data, we find that the targets have electron temperatures of at least 3 keV. \textcopyright{} 1996 The American Physical Society.

We have successfully employed isoelectronic line ratios to measure the electron temperature in gas-filled hohlraums and ‘‘gas bags’’ shot with the Nova laser. Isoelectronic line ratios are well suited to this measurement because they are relatively insensitive to radiation field effects (in hohlraums), opacity, transients, and variations in electron density compared to conventional line ratios. Targets were designed to produce plasma parameters Te∼3 keV and Ne∼1021 cm−3 over a scale length of ∼2 mm. Collisional-radiative, transient K-shell atomic kinetics calculations including line transfer were performed by post-processing the Lasnex results. By comparing these calculations with experimental data, we infer electron temperatures of at least 3 keV for both types of targets.

Stimulated Brillouin scattering (SBS) has been measured from hohlraums with plasma conditions similar to those predicted for high gain targets. The plasmas differ from the more familiar exploding foil or solid targets in being hot (3 keV), high electron density (1${0}^{21}$ c${\mathrm{m}}^{--3}$), stationary, confined within a gold cylinder, and uniform over greater than 2 mm. Peak SBS backscatter is 3% in these hohlraums for an interaction beam with intensities of $\left(1\ensuremath{-}4\right)\ifmmode\times\else\texttimes\fi{}{10}^{15}$ W/c${\mathrm{m}}^{2}$, laser wavelength equal to 0.351 \ensuremath{\mu}m, $f/4$ or $f/8$ focusing optics, and a variety of beam smoothing implementations.

The development of a plasma environment that is appropriate for the study of laser-plasma processes in laser-fusion plasma is reported. A material (titanium) with medium atomic number (Z) was used to provide x-ray measurements of radial and axial plasma symmetry as well as electron temperature. The electron density evolution was measured using stimulated scattering processes and odd half-harmonic generation from probe lasers of different wavelengths. The plasmas were created by two-sided irradiation of thin foils with 24 kJ of 351 nm laser light. When the peak electron density had decayed to about 4×1020 cm−3, the density profile was estimated to have a full width at half-maximum of 2 mm and the electron temperature was measured to be about 3 keV using K-shell spectroscopy. Two-dimensional computer simulations were found to reproduce some features of both electron density and temperature evolution.

Stimulated Brillouin backscatter from large scale-length gas-filled targets has been measured on the Nova laser. These targets were designed to approximate conditions in indirect drive ignition target designs in underdense plasma electron density (ne∼1021/cm3), temperature (Te≳3 keV), and gradient scale lengths (Ln∼2 mm, Lv≳6 mm) as well as calculated gain for stimulated Brillouin scattering (SBS). The targets used in these experiments were gas-filled balloons with polyimide walls (gasbags) and gas-filled hohlraums. Detailed characterization using x-ray imaging and x-ray and optical spectroscopy verifies that the calculated plasma conditions are achieved. Time-resolved SBS backscatter from these targets is <3% for conditions similar to ignition target designs.

We have developed spectrographs to measure the electron temperature in gas-filled targets and low-density foams, and find it to nominally fall in the 2–4-keV range. The instrument we designed, built, and fielded can simultaneously record the Ti Heα and Cr Heα line emission. After compensating for the instrumental response, we can estimate the electron temperature from this line ratio to within ±15%.

Large plasmas are created by illuminating gas-filled thin-walled balloon-like targets using the Nova laser [E. Campbell et al., Rev. Sci. Instrum. 57, 2101 (1986)]. The targets consist of a 5000–6000 Å skin surrounding 1 atm of neopentane, which, when ionized, becomes a plasma with an electron density of 1021 electrons/cm3. X-ray images of the gas bag target are used to evaluate the size and uniformity of the plasma by comparison with LASNEX [R. M. More, J. Quant. Spectrosc. Radiat. Transfer 27, 345 (1982)] simulations. The gas bags are heated with converging and diverging beam spots. The most uniform plasmas are created by illuminating the target with large converging beam spots that overlap to cover most of the surface of the gas bag. The gas bag plasma is heated to a peak temperature of approximately 3.5 keV, with 25 kJ of 3ω laser light in a 1 ns square pulse.