[en] Thomson scattering measurements of the electron temperature in laser- produced gold plasmas are presented. We irradiated a flat gold disk target with one laser beam of the Nova laser facility. A second laser beam probed the plasma at a distance of 500μm with temporally resolved Thomson scattering. The electron temperature measurements are compared with hydrodynamic simulations using the code LASNEX for experiments applying smoothed and unsmoothed heater beams. In case of an unsmoothed heater beam the simulations predict temperatures which are about 40% higher than our measured data. Although the agreement is improved for a smoothed heater beam, discrepancies exist in the decay phase of the plasma. We discuss possible explanations for these observations

[en] The spectral line profiles of ionized emitters in plasmas play an important role in the calculation of opacity, for short-wavelength laser studies, and for the diagnostics of inertial confinement fusion plasmas. Sophisticated theoretical methods and modeling have been advanced and applied in recent years to calculate spectral line profiles in the limits where broadening by electron collisions or by ion microfield dominates. Here, the authors describe recent measurements of spectral line profiles of a z-pinch experiment employing precision plasma diagnostic techniques. In particular, the electron-collisional-broadened 2s--2p transitions in B_III have been investigated because their line profiles provide an excellent test for electron-impact line shape theories and electron collision strength calculations. Although they find good agreement with semiclassical calculations, a factor of two discrepancy with the most elaborate quantum-mechanical five-state close coupling calculations is observed. They discuss the experimental error estimates of the various measured quantities and show that the observed discrepancy can not be explained by experimental shortcomings. They further discuss measurements of non-isolated spectral lines of some Δn = 1 transitions in C_IV--O_VI. For these transitions ion broadening dominates. Excellent agreement for the whole line profile with line broadening calculations is obtained for all cases only when including ion dynamic effects. The latter are calculated using the frequency-fluctuation model and account for about 10--25% of the line width of the considered ions

[en] Until now the thermodynamic and structural properties of hydrogen continue to be understood unsatisfactory. A number of complex high pressure phases at relatively low temperatures has been confirmed (1). However, conclusive answers on the existence of a plasma phase transition, the dissociation of hydrogen molecules at high densities, the metallization in the solid, and the melting line for pressures above 70GPa are still missing. A particularly interesting behavior has been predicted for the melting line at high pressures where it has a maximum and its slope changes sign (2). In Ref. (3), we have shown that these states can be created using cylindrical compression driven by heavy ion beams. Employing ab initio simulations (4) and experimental data, a new wide range equation of state for hydrogen was constructed (3). This new hydrogen EOS combined with hydrodynamic simulations is then used to describe the compression of hydrogen in LAPLAS targets (5) driven by heavy ion beams to be generated at the FAIR. The results shown in Fig. 1 indicate that the melting line up to its maximum as well as the transition from molecular fluids to fully ionized plasmas can be tested. By carefully tuning the number of particles in the beam, the compression can be adjusted to yield states at the solid-liquid phase transition (compare panels (a) and (b) in Fig. 1). This allows one to test the shape of the melting line beyond its maximum. It was demonstrated (3) that x-ray scattering (6) can be used to distinguish between the molecular solid and liquid phases as well as the metallic states. Hydrodynamic simulations have also highlighted the importance of temperature diagnostics, as it is more sensitive to the EOS than the density based diagnostic methods. Different materials have been considered as absorber. Although lead might seem to be the natural choice, the simulations show that aluminium is also a feasible option if slightly less compression is sufficient. Moreover, aluminium offers further options for testing by x-ray scattering and, thus, might be favorable compared to lead drivers. In summary, valuable information on the properties of high-density hydrogen can be obtained by dynamic compression with heavy ion beams. The long standing questions of the plasma phase transition, melting, and metallization can be addressed. The calculated Jupiter isentrope shown in Fig. 1 indicates that such experiments would be also highly beneficial for the giant planet modeling

[en] 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. The authors 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, they examine the time-dependence of spectroscopic plasma diagnostics

[en] We describe recent measurements of spectral line profiles of a z-pinch experiment employing precision plasma diagnostic techniques. In particular, the electron-collisional-broadened 2s-2p transitions in BIII have been investigated because their line profiles provide an excellent test for electron-impact line shape theories and electron collision strength calculations. Although we find good agreement with semiclassical calculations, a factor of two discrepancy with the most elaborate quantum-mechanical five-state close coupling calculations is observed. We discuss the experimental error estimates of the various measured quantities and show that the observed discrepancy can not be explained by experimental shortcomings. We further discuss measurements of non-isolated spectral lines of some Δn=1 transitions in CIV-OVI. For these transitions ion broadening dominates. Excellent agreement for the whole line profile with line broadening calculations is obtained for all cases only when including ion dynamic effects. The latter are calculated using the frequency-fluctuation model and account for about 10 endash 25% of the line width of the considered ions. copyright 1996 American Institute of Physics

[en] The plasma conditions in isochorically heated beryllium are measured by x-ray Thomson scattering in the collective regime with a Cl Ly-α x-ray source at 2.96 keV. In addition to the down-shifted plasmon shape which provides electron density and temperature information, an up-shifted plasmon signal is observed allowing a model independent determination of the plasma temperature from the detailed balance relation

[en] Diagnostics have been developed and fielded at the Nova laser facility that image scattered light in the vicinity of the final laser focusing lens. The absolute calibration of optical components exposed to the target debris have been achieved by a combination of routine in situ calibration and maintenance. The scattering observed from plasmas relevant to ignition experiments indicates that light scattered just outside the lens can be larger than that collected by the lens, and is a significant factor in the energy balance when the f number is high

[en] 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

[en] We have performed x-ray spectroscopic experiments in homogeneous gas bag plasmas where we independently measure the temperature with Thomson scattering. We find that collisional radiative (kinetics) modeling of the intensities of the He-β line and its dielectronic capture satellites is generally in agreement with the measured spectra. On the other hand, for the particular case of satellites arising from inner-shell electron collisional excitation, we find discrepancies of up to a factor of two between experiment and kinetics models. We have ruled out possible effects on the line emission due to plasma gradients, radiative transport, and suprathermal electron excitation leaving errors in the atomic physics modeling to be the most likely explanation. The determination that there are problems with the collisionally populated states is important for the interpretation of inertial confinement fusion capsule implosions where electron densities and temperature have been measured using the spectral line shape of the He-β transition of Ar XVII. The analysis of the implosion data has required Stark broadening calculations coupled to a kinetics model to calculate the detailed line intensities and widths. Despite remaining discrepancies, the good agreement between the experimental dielectronic capture satellites and the HULLAC calculations suggests that HULLAC is a more appropriate code for the construction of the kinetics models of the He-β complex from high density plasmas than previously used codes (e.g. MCDF). HULLAC results in higher temperatures for the implosion conditions of Ref.(5,6) in closer agreement with the 2-D radiation hydrodynamic modeling and other spectroscopic techniques. These results indicate that benchmarking kinetics codes with Thomson scattering is an important area in present ICF research

[en] Simultaneous Thomson scattering measurements of collective electron-plasma and ion-acoustic fluctuations have been utilized to determine ion species fraction from laser produced CH plasmas. The CH₂ foil is heated with 10 laser beams, 500 J per beam, at the Omega Laser facility. Thomson scattering measurements are made 4 mm from the foil surface using a 30 J 2ω probe laser with a 1 ns pulse length. Using a series of target shots the plasma evolution is measured from 2.5 ns to 9 ns after the rise of the heater beams. Measuring the electron density and temperature from the electron-plasma fluctuations constrains the fit of the two-ion species theoretical form factor for the ion feature such that the ion temperature, plasma flow velocity and ion species fraction are determined. The ion species fraction is determined to an accuracy of ±0.06 in species fraction.