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It has become apparent in the last few years that the surface contamination on laser-acceleration targets is a major impediment to the acceleration of the actual target ions. To this end we have performed experiments at the Los Alamos Trident Laser facility using one arm of the Trident laser at 150 ps to ablatively clean targets that are subsequently irradiated by the Trident TW Short-pulse arm to accelerate the bulk target ions to high energies. The 150 ps ablation pulse rids the rear of the target of its omnipresent surface contamination layer allowing the short-pulse to illuminate the target and accelerate ions via the Target Normal Sheath Acceleration (TNSA) mechanism. Our experimental results are compared to the LASNEX code to validate and improve our predictive capabilities for future acceleration experiments.

We report on measurements of source sizes and charge state distributions of ions accelerated from thin foils irradiated by ultrashort (100–300 fs) high-intensity (1-6×1019 W/cm2) laser pulses. The source sizes of proton and carbon ion beams originating from hydrocarbon contaminants on the surfaces of 5 μm thick aluminum foils were investigated using the knife-edge method. For low-energy protons and low-carbon charge states, the source area was found to exceed the focal spot area by a factor of 104. For the determination of charge state distributions, sandwich targets consisting of a 25 μm thick tungsten layer, a 2-nm thin beryllium layer, and again a tungsten layer whose thickness was varied were used. These targets were resistively heated to remove the light surface contaminants. Peaked energy spectra of oxygen and argon ions corresponding to the equilibrium distribution after propagation through matter were observed.

We have designed and produced hot, millimeter-scale, high-{ital Z} plasmas of interest for National Ignition Facility hohlraum target design. Using a high-{ital Z} gas fill produces electron temperatures in the 3.5{endash}6-keV range, the highest temperatures measured to date for high-density (10{sup 21} e/cm{sup 3}) laser-heated plasmas, and much higher than the 3 keV found for low-{ital Z} (neopentane) fills. These measurements are in good agreement with the target design calculations, and the {ital L}-shell spectroscopic approach used to estimate the electron temperature has certain advantages over traditional {ital K}-shell approaches. {copyright} {ital 1999} {ital The American Physical Society}

Data from a pinhole camera and a transmission grating spectrograph are used in multi-TW laser irradiance of thin metal films to assess the maximum laser spot size and to show tenths of a percent conversion of laser light to K-, L-, and M-band x rays. The distribution of target debris, an operational issue for the survivability of an unshielded parabola in a large laser system, is revealed by x-ray fluorescence measurements of witness samples. At the 25-J, 30-TW level, we find little evidence of damage to the f/3 parabola with an angle of incidence on target greater than 22°.

Capsules driven with polar drive [1, 2] on the National Ignition Facility [3] are being used [4] to study mix in convergent geometry. In preparation for experiments that will utilize deuterated plastic shells with a pure tritium fill, hydrogen-filled capsules with copper- doped deuterated layers have been imploded on NIF to provide spectroscopic and nuclear measurements of capsule performance. Experiments have shown that the mix region, when composed of shell material doped with about 1% copper (by atom), reaches temperatures of about 2 keV, while undoped mixed regions reach about 3 keV. Based on the yield from these implosions, we estimate the thickness of CD that mixed into the gas as between about 0.25 and 0.43 μm of the inner capsule surface, corresponding to about 5 to 9 μg of material. Using 5 atm of tritium as the fill gas should result in over 1013 DT neutrons being produced, which is sufficient for neutron imaging [5].

Summary form only given. An understanding of the material dynamics and EoS characteristics of copper-doped beryllium (Be-Cu) ablators is critical for several ignition designs for the National Ignition Facility (NIF). Beryllium offers several advantages as an ablator: (a) high density, (b) low heat capacity, and (c) low opacity. In addition, dopants can be used to optimize these characteristics, for example, copper increases the density and opacity. In such a design, the Be-Cu ablator is subjected to thermal and soft X-ray radiation, delivering a sequence of shocks which compress a deuterium-tritium capsule. The first shock is expected to be between 0.5 and 8.0 Mbar. Be-Cu is predicted to melt on the Hugoniot between 1 and 2 Mbar and may depend upon the time scale. The anisotropic mechanical and thermal expansion properties of Be-Cu may introduce velocity fluctuations as the microstructure is loaded, and may then seed Rayleigh-Taylor instabilities. The uncertainty in Be-Cu melt and instability-growth dependence upon microstructure impacts the predictive capabilities for capsule performance. We have developed and fielded a series of experiments at the Omega laser facility that closely replicate the NIF-foot hohlraum conditions expected for a Be-Cu ablator. The experiments aim to investigate the seeding of instabilities by microstructure. In these experiments, a holhraum is rapidly brought up to a radiation temperature of 70-90 eV and held there for 2.5-3.2 ns. After ~3.0 ns, the temperature is raised to 120-150 eV in order to drive instabilities. Using 25-70 micron thick Be-0.9%Cu samples mounted on one end of the hohlraum, we performed free-surface velocimetry and pyrometry measurements during the foot of the pulse. We will present the velocity and pyrometry data along with inferred pressure, and discuss potential implications for Be-Cu capsule performance at NIF

Order-of-magnitude anomalously high intensities for two-electron (dielectronic) satellite transitions, originating from the He-like 2s(2) 1S0 and Li-like 1s2s(2) (2)S(1/2) autoionizing states of silicon, have been observed in dense laser-produced plasmas at different laboratories. Spatially resolved, high-resolution spectra and plasma images show that these effects are correlated with an intense emission of the He-like 1s3p 1P-1s(2) 1S lines, as well as the K(alpha) lines. A time-dependent, collisional-radiative model, allowing for non-Maxwellian electron-energy distributions, has been developed for the determination of the relevant nonequilibrium level populations of the silicon ions, and a detailed analysis of the experimental data has been carried out. Taking into account electron density and temperature variations, plasma optical-depth effects, and hot-electron distributions, the spectral simulations are found to be not in agreement with the observations. We propose that highly stripped target ions (e.g., bare nuclei or H-like 1s ground-state ions) are transported into the dense, cold plasma (predominantly consisting of L- and M-shell ions) near the target surface and undergo single- and double-electron charge-transfer processes. The spectral simulations indicate that, in dense and optically thick plasmas, these charge-transfer processes may lead to an enhancement of the intensities of the two-electron transitions by up to a factor of 10 relative to those of the other emission lines, in agreement with the spectral observations.

Measurements of the total energy carried by fast ablator-ions in direct-drive implosions on OMEGA have been conducted using magnetic and Thomson Parabola spectrometers. It is shown that the total laser energy lost to fast ablator-ions for plastic and glass targets is comparable and that it is a modest fraction of the incident laser energy (≲1%). These measurements have been used to infer a non-linear, voltage-dependent target capacitance (∼0.1 nF) associated with the space-charge that accelerates the fast-ions.

The geometry of inertial confinement fusion (ICF) capsules makes them susceptible to various types of hydrodynamic instabilities at different stages during an ICF implosion. From the beginnings of ICF research, it has been known that grain-level anisotropy and defects could be a significant source of instability seeding in solid beryllium capsules. We report on experiments conducted at the Trident laser facility [S. H. Batha et al., Rev. Sci. Instrum. 79, 10F305 (2008)] to measure dynamic surface roughening from hard x-ray preheat due to anisotropic thermal expansion. M-band emission from laser-produced gold plasma was used to heat beryllium targets with different amounts of copper doping to temperatures comparable to ICF ignition preheat levels. Dynamic roughening measurements were made on the surface away from the plasma at discrete times up to 8 ns after the beginning of the drive pulse using a surface displacement interferometer with nanometer scale sensitivity. Undoped large-grained targets were measured to roughen between 15 and 50 nm rms. Fine-grained, copper-doped targets were observed to roughen near the sensitivity limit of the interferometer. The results of this work have shed light on the effects of high-Z doping and microstructural refinement on the dynamics of differential thermal expansion and have shown that current ICF capsule designs using beryllium are very effective in reducing preheat related roughening ahead of the first shock.

We have characterized kilo-electron-volt (keV) emission from Al plasmas for various laser illuminations at the OMEGA laser with the goal of optimizing the ability to backlight low-atomic-number materials such as beryllium for fusion ignition studies. The plasma is diagnosed by spectral-measurement comparisons to detailed theoretical atomic physics models. It is found that a significant fraction of the radiation is due to the x-ray continuum, that the electron temperature Te depends weakly on laser energy and power, and that the conversion efficiency to Lyman α (Lα, the N=2→1 transition in H-like Al) at 1.73 keV is reduced as laser energy is increased. As the number of beams is increased, the extra laser energy goes into a larger, higher-density plasma in which He-like and H-like ions are more effectively ionized.

A multiple-laboratory campaign is underway to qualify beryllium as a fusion capsule ablator for the National Ignition Facility [Moses and Wuest, Fusion Sci. Technol. 43, 420 (2003)]. Although beryllium has many advantages over other ablator materials, individual crystals of beryllium have anisotropic properties, e.g., sound speed, elastic constants, and thermal expansion coefficients, which may seed hydrodynamic instabilities during the implosion phase of ignition experiments. Experiments based on modeling have begun at the OMEGA laser [Boehly, McCrory, Verdon et al., Fusion Eng. Design 44, 35 (1999)] to create a test bed for measuring instability growth rates with face-on radiography of perturbed beryllium samples with the goal of establishing a specification for microstructure in beryllium used as an ablator. The specification would include the size and distribution of sizes of grains and voids and the impurity content. The experimental platform is a 4kJ laser-heated (for ∼6ns) hohlraum that is well mod...

Information was obtained on the nature of Ru(IV) in perchloric acid through solubility studies. The average charge on the aqueous species is ⁺2. Extensive polymerization was observed in these solutions, and the monomer ruthenyl, RuO²⁺, was identified and isolated as a constituent. (auth)

The helium-ion-induced fission excitation functions of rhenium, lutetium, and thulium have been measured in the energy interval of 30 to 80 MeV using a "fission-track" technique with plastic films as detectors. By analyzing the ratio $\frac{{\ensuremath{\Gamma}}_{f}}{{\ensuremath{\Gamma}}_{n}}$, which measures competition between fission and neutron emission, fission thresholds of 22.4, 23.6, 27.5, and 28.7 MeV have been determined for ${\mathrm{Ir}}^{189}$, ${\mathrm{Ir}}^{191}$, ${\mathrm{Ta}}^{179}$ and ${\mathrm{Lu}}^{173}$, respectively. These values are obtained using a level-density parameter ${a}_{f}=\frac{A}{10}$, with the uncertainty of this choice introducing a possible error of \ifmmode\pm\else\textpm\fi{}2.5 MeV in the calculated barriers. The thresholds, which are of particular interest because the nuclides involved are removed from the closed-shell region, are in agreement with predictions of a recently proposed semi-empirical mass formulation based on a charged liquid drop. Correlations are given showing the relationship of $\frac{{\ensuremath{\Gamma}}_{f}}{{\ensuremath{\Gamma}}_{n}}$ with $\frac{{Z}^{2}}{A}$ and ${{E}_{f}}^{\ensuremath{'}}\ensuremath{-}{{B}_{n}}^{\ensuremath{'}}$, where ${{E}_{f}}^{\ensuremath{'}}$ and ${{B}_{n}}^{\ensuremath{'}}$ are the effective fission barrier and the neutron binding energy. The results suggest that shell effects tend to persist even at excitation energies of 30 MeV. Comparisons of the correlations with heavy-element data point out the marked discontinuity near $Z=90$, and support the general two-mode fission hypothesis.

The relative contributions of energetic neutrons and γ- and β- rays to the radiation decomposition of crystalline KBrO3 in the Oak Ridge graphite pile were determined as approximately 20, 40, and 40%, respectively. Decomposition yields (i.e., "G''-values) for β-rays and pile γ-rays were 1.0 plus or minus 0.1 molecule per 100 e.v. energy absorbed, while for energetic neutrons yields varying from 23 to 30, dependent on neutron energy, were found. The much greater efficiency for decomposition by fast neutrons was attributed to the mechanism whereby these particles transfer energy to bromate radicals.

The heats of oxidation of ReCl/sub 3/(c) and ReBr/sub 3/(c) by basic hypochlorite were determined. From these data the heats of formation at 25 deg were calculated to be: ReCl/sub 3/(c), -63.0 plus or minus 0.8 kcal mole/sup -1/ and ReBr/sub 3/(c), -39.3 plus or minus 0.8 kcal mole/sup -1/. Free energy and entropy estimates also are given. (auth)

The 44pi 6 wt.% Ru-U all - coincidence technique has been used to study the efficiency of the so-called 4 The effects of proportional counter. In most cases the counting effieiency varies approximately exponentially with the energy, dripping in the case of cobalt-60 to ~90%. The advantages of the technique are discussed and recommendations made as to a primary standardization method. (auth)

We present analysis and LASNEX modeling of two experiments designed to explore the mechanisms and scaling of laser-plasma coupling in high-Z plasmas. The first used layered Au-on-CH spheres irradiated symmetrically using the Omega (Laboratory for Laser Energetics) 0.35 µm laser to observe the x-ray emission and energy penetration in gold plasmas. Measurements of the subkilovolt and kilovolt emission from targets with varying Au-coating thicknesses were made using diagnostics of varying spectral, temporal, and spatial resolution. The results indicate that the x-ray conversion efficiency is a function of target size, with larger targets yielding x-ray emission in excellent agreement with calculations. The x-ray emission fall-off with decreasing gold thickness agrees well with predictions. The second experiment used the Novette (Lawrence Livermore National Laboratory) laser to irradiate solid gold disk targets, examining wavelength scaling to 0.26 µm. The measured subkilovolt x-ray emission is in good agreement with calculations using mildly inhibited thermal electron transport, indicating enhanced target coupling, compared with previous experiments using smaller spot sizes. The experiment also indicates very low suprathermal electron populations, on the order of 0.1% at about 30 keV effective temperature. Finally, we present preliminary plans and designs for experiments which will use the Aurora 5 kJ, 5 ns, 0.25 µm KrF laser now being constructed at Los Alamos.

By use of new techniques in isotope calibration, and scintillation spectrometry, a large well-type scintillation crystal counter has been calibrated very accurately. This now readily available counting system can be used routinely for mixed isotope analysis, for absolute counting of isotopes, and for decay scheme analysis. Accurate absolute counting of electron-capture isotopes is a further possible application. (auth)