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[en] Lithium as a plasma-facing material has attractive features, including a reduction in the recycling of hydrogenic species and the potential for withstanding high heat and neutron fluxes in fusion reactors. Dramatic effects on plasma performance with lithium-coated plasma-facing components (PFC's) have been demonstrated on many fusion devices, including TFTR, T-11M, and FT-U. Using a liquid-lithium-filled tray as a limiter, the CDX-U device achieved very significant enhancement in the confinement time of ohmically heated plasmas. The recent NSTX experiments reported here have demonstrated, for the first time, significant and recurring benefits of lithium PFC coatings on divertor plasma performance in both L- and H- mode regimes heated by neutral beams.
[en] Cross section and analyzing power excitation functions for the 26Mg(anti p,p')26Mg reaction were obtained for the ground state and three excited states in 26Mg in the energy range Ep = 5.5 to 17.5 MeV in 50 keV intervals and at lab angles of 1200, 1400, and 1600. Angular distributions for the cross sections and analyzing power were also measured at many energies throughout this energy range. The measurements were analyzed with standard techniques involving autocorrelations and cross correlations. The standard statistical analyses were ambiguous as indicators of significant deviations from the predictions of statistical theory. Distribution-free tests tended to support the conclusion that the structure in the excitation functions for inelastic scattering was not entirely due to chance coherences among random nuclear amplitudes from overlapping continuum states. The experimental data had to be trend-reduced before these tests were applied, however, and this presented many difficulties. In particular, it was not possible to determine the direct-reaction background in an unambiguous way. Trends due to the opening of new reaction channels or a changing density of compound nucleus levels were equally difficult to treat. Thus, the conclusions about nonrandom structure in the experimental excitation functions are suggestive, but not definitive
[en] Lithium as a plasma-facing material has many attractive features, including a reduction in the recycling of hydrogenic species and the potential for withstanding high heat and neutron fluxes in fusion reactors. Recent NSTX experiments have shown, for the first time, significant and recurring benefits of lithium coatings on plasma-facing components (PFC's) to the performance of divertor plasmas in both L- and H- mode confinement regimes heated by high-power neutral beams. They included decreases in the plasma density and inductive flux consumption, and increases in the electron temperature, ion temperature, energy confinement time, and DD neutron rate. Extended periods of MHD quiescence were also achieved, and measurements of the visible emission from the lower divertor showed a reduction in the deuterium, carbon, and oxygen line emission. Other salient results with lithium evaporation included a broadening of the electron temperature profile, and changes in edge density gradients that benefited electron Bernstein wave coupling. There was also a reduction in ELM frequency and amplitude, followed by a period of complete ELM suppression. In general, it was observed that both the best and the average confinement occurred after lithium deposition and that the increase in WMHD occurs mostly through an increase in We. In addition, a liquid lithium divertor (LLD) is being installed on NSTX this year. As the first fully-toroidal liquid metal divertor target, experiments with the LLD can provide insight into the behavior of metallic ITER PFC's should they liquefy during high-power divertor tokamak operations. The NSTX lithium coating and LLD experiments are important near-term steps in demonstrating the potential of liquid lithium as a solution to the first-wall problem for both magnetic and inertial fusion reactors
[en] The charge exchange diagnostic for TFTR requires simultaneous multispecie (H+, D+, γ+) analysis of particles in the energy range of 0.5 - 150 keV. The analyzer design chosen to provide this capability employs a wide gap semi-circular region of superimposed parallel electric and magnetic fields to accomplish mass and energy resolution, respectively. Combined with a large area, multi-anode microchannel plate detector, this arrangement will enable the energy distributions of protons, deuterions, and tritons to be measured concurrently as a function of time during each discharge. A computer simulation program for calculating ion trajectories through the analyzer was written that includes a realistic model of the magnetic and electrostatic fringe fields. This report presents the results of a study of the proposed E parallel B analyzer, and it reveals that the fringe fields are not detrimental to the performance of the analyzer
[en] Ion temperature profiles with a time resolution of 2-5 ms have been measured on PBX by charge exchange recombination spectroscopy (CXRS) and a neutral particle charge exchange analyzer (NPA). The sightlines of both diagnostics crossed the trajectory of a near-perpendicular heating beam, which enhanced the local neutral density (Α signal strength) and provided spatial resolution. The time resolution of these two independent techniques is sufficient to see sawtooth oscillations and other MHD activity. The NPA results, with the contribution from the slowing-down heating beam particles subtracted, are compared with CXRS. Effects of these phenomena on the toroidal rotation velocity profile, vφ (r), are clearly observed by CXRS. For example, a sharp drop in the central vφ occurs at the sawtooth crash, followed by a linear rise during the quiescent phase. The techniques are described and sources of error are described
[en] Ion cyclotron radio-frequency heating experiments were performed with a 3He minority ion species in a 4He majority plasma in the Princeton Large Torus. The energetic 3He ion ''tail'' was measured directly with a charge exchange neutral analyzer for the first time. Comparisons with bounce-averaged quasi-linear calculations suggest a modestly peaked radi-frequency power deposition profile. The double charge exchange process 3He++ /plus/ 4He0 /plus/ 3He0 /plus/ 4He++ demonstrated in these measurements may be useful as part of an alpha particle diagnostic in a fusion reactor experiment. 18 refs., 4 figs
[en] Recent experiments on the National Spherical Torus eXperiment (NSTX) have shown the benefits of solid lithium coatings on carbon PFC's to diverted plasma performance, in both Land H- mode confinement regimes. Better particle control, with decreased inductive flux consumption, and increased electron temperature, ion temperature, energy confinement time, and DD neutron rate were observed. Successive increases in lithium coverage resulted in the complete suppression of ELM activity in H-mode discharges. A liquid lithium divertor (LLD), which will employ the porous molybdenum surface developed for the LTX shell, is being installed on NSTX for the 2010 run period, and will provide comparisons between liquid walls in the Lithium Tokamak eXperiment (LTX) and liquid divertor targets in NSTX. LTX, which recently began operations at the Princeton Plasma Physics Laboratory, is the world's first confinement experiment with full liquid metal plasma-facing components (PFCs). All materials and construction techniques in LTX are compatible with liquid lithium. LTX employs an inner, heated, stainless steel-faced liner or shell, which will be lithium-coated. In order to ensure that lithium adheres to the shell, it is designed to operate at up to 500 - 600 oC to promote wetting of the stainless by the lithium, providing the first hot wall in a tokamak to operate at reactor-relevant temperatures. The engineering of LTX will be discussed.
[en] Compact electrostatic charge-exchange analyzers have been constructed for installation in areas of high magnetic fields and restricted access near tokamak fusion devices. The analyzers employed carbon stripping foils, and have been calibrated for proton energies between 1 and 70 keV. They have been successfully used to study charge-exchange losses in auxiliary-heated tokamak plasmas
[en] An improved design for the present PDX thermal charge exchange analyzer (MACE) has been proposed by one of the authors, in which the five cylindrical electrostatic plates for mass separation are replaced by a single flat, electrostatic deflection plate. An existihg Monte Carlo code that simulated the passage of ions through the MACE analyzer was modified to examine the feasibility of this change. The resulting calculations were used to optimize detector positions and collimation requirements. The first analyzer to be placed on PDX will be of the old design, similar to the present PLT analyzer. However, if the design reported here is successful on the test stand, the future PDX analyzers will all be of the new, single electrostatic plate variety. A further advantage will be the ability to install as many as ten detectors instead of the current five, thus providing twice as many energy channels for each shot. Also, both mass species (H, D) can be measured concurrently, if desired
[en] The horizontally-scanning charge exchange analyzer on the Princeton Large Torus (PLT) was used to measure fast co-moving ions during counter-injection of neutral beams. The large flux of charge exchange neutrals observed under these circumstances exhibited a sharp cutoff as the analyzer was moved toward more parallel radii of tangency. At a fixed angle and beam energy, the cutoff showed a strong dependence on the plasma current. Monte-Carlo calculations using a Fokker-Planck formalism and full toroidal geometry give substantive agreement with the experimental data, indicating that neoclassical effects on neutral beam injected ions were directly observed