[en] Ion Bernstein wave experiments are carried out on the Alcator C tokamak to study wave excitation, propagation, absorption, and plasma heating due to wave power absorption. It is shown that ion Bernstein wave power is coupled into the plasma and follows the expected dispersion relation. The antenna loading is maximized when the hydrogen second harmonic layer is positioned just behind the antenna. Plasma heating results at three values of the toroidal magnetic field are presented. Central ion temperature increases of ΔT/sub i//Ti /approx lt/ 0.1 and density increases Δn/n < 1 are observed during rf power injection of up to 180kW at a frequency of 183.6 /times/ 10⁶s/sup /minus/1/ for plasmas within the density range 0.6 /times/ 10²⁰m/sup /minus/3/ ≤ /bar n//sub e/ ≤ 4 /times/ 10²⁰m/sup /minus/3/ and magnetic fields 2.4 ≥ ω/Ω/sub H/ ≥ 1.1. The density increases is usually accompanied by an improvement in the global particle confinement time relative to the Ohmic value. The ion heating rate is measured to be ΔT/sub i//P/sub rf/ ≅ 2-4.5 eV/kW at low densities. At higher densities /bar n//sub e/ ≤ 1.5 /times/ 10²⁰m/sup /minus/3/ the ion heating rate dramatically decreases. It is shown that the decrease in the ion heating rate can be explained by the combined effects of wave scattering through the edge turbulence and the decreasing on energy confinement of these discharges with density. The effect of observed edge turbulence is shown to cause a broadening of the rf power deposition profile with increasing density. It is shown that the inferred value of the Ohmic ion thermal conduction, when compared to the Chang-Hinton neoclassical prediction, exhibits an increasing anomaly with increasing plasma density

[en] Scattered light at three-halves of the incident laser frequency from solid targets is observed at five different angles. When the incident laser intensity is low enough, rescattering of two plasmon decay (TPD) instability electron plasma waves by ion acoustic waves is not significant. In this regime, Thomson scattering measurements of the electron temperature and the plasma flow velocity allow quantitative comparison of the angular dependence of the spectrum to theory

[en] We use thermal conduction models to investigate the effects of tailored IR heating on the fuel layer symmetry within a target capsule supported inside of a National Ignition Facility (NIF) hohlraum. We calculate the layer thickness profile that would result from the IR heat distribution alone and in combination with additional temperature shimming of the cylindrical hohlraum wall. We use the same model to study the effect of convection within the high density tamping gas in the hohlraum. A seven-region model was developed to evaluate how effective additional thin film convection barriers may be in damping convection with the higher power dissipation introduced by IR heating

[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] An ICRF experiment is in progress on the Alcator C tokamak at power levels up to 100 kW. Up to 600 kW of RF power is available in the range 180 - 215 MHz with pulse durations up to 100 ms. The target plasma has a reduced minor radius (12.5 cm) and an ohmic input power comparable with the RF power. The antenna consists of two pairs of half-turns connected to form one wide full turn enclosing the plasma, and is fed by two elongated transmission lines which fill one horizontal diagnostic port. The upper and lower elements are one half wave-length long and are tuned independently by triple stub tuners to allow relative phase shifts to be introduced. Low power (<1 Watt) experiments have been conducted in both the hydrogen second harmonic regime (6 -7 T, 180 - 200 MHz) and the fundamental hydrogen minority regime (10 T, 150 MHz). The radiation resistance exhibits eigenmode peaks which disappear when a resonant hydrogen minority is present. Preliminary measurements indicate that the radiation resistance is typically 0.1 - 0.2 Ω in vacuum and 1-2 Ω when plasma is present. This can be compared with a theoretical value of 5 Ω for half the antenna at n-bar/sub e/=4 x 10/sup 14/ cm/sup -3/ with the expectation that the density accounts for a considerable part of the discrepancy

[en] We investigate the actively controlled thermal environment of a National Ignition Facility (NIF) cryogenic hohlraum using measurements and calculations of hydrogen ice equilibrium. Thermal modeling of the hohlraum temperature field is shown to be consistent with measurements of the ice distribution. These results demonstrate the ability to accurately model and control the thermal environment in an NIF hohlraum

[en] The effect of random phase plate (RPP) beam smoothing on stimulated Brillouin scattering (SBS) backscattered light in exploding foil plasmas is investigated experimentally. The experiments consist of measuring the backscattered SBS emission excited by an unsmoothed and a RPP smoothed interaction beam impinging on a preformed plasma. A Ti or CH plasma is performed with typically 2500 J of 0.527 μm RPP smoothed laser light with a square pulse of 1 ns. The interaction laser focuses on the centre of the preformed plasma with a duration of 1 ns, 0.527 μm wavelength, ∼ 2500 J, and an adjustable delay time. At least 15 times less backscattered SBS energy is measured with an RPP. (author). 7 refs, 2 figs

[en] Production of fast ion tails in the minority species of the Alcator C plasma has been observed on the charge exchange neutral particle spectra for both ICRF fast wave minority heating experiments and in directly launched ion Bernstein wave (IBW) experiments. The behavior of these fast ions is compared as a function of density, concentration, and rf power

[en] Recent NIF indirect-drive experiments have shown significant Raman scattering from the inner beams. NIF data has motivated improvements to rad-hydro modeling, leading to the 'high flux model' (M. D. Rosen et al., HEDP 7, 180 (2011)). Cross-beam energy transfer (P. A. Michel et al., Phys. Plasmas 17, 056305 (2010) in the laser entrance hole is an important tool for achieving round implosions, and is uniformly distributed across the laser spot in rad-hydro simulations (but not necessarily in experiments). We find the Raman linear gain spectra computed with these plasma conditions agree well in time-dependent peak wavelength with the measured data, especially when overlapping laser-beam intensities are used. More detailed, spatially non-uniform modeling of the cross-beam transfer has been performed. The resulting gains better follow the time history of the measured backscatter. We shall present the impact of spatially non-uniform energy transfer on SRS gain. This metric is valid when amplification is in a linear regime, and so we shall also present an assessment of whether electron trapping in Langmuir waves can play a role in these shots.

No abstract available