[en] In DIII-D, visible spectroscopic measurements of the He II 468.6 nm and C VI 529.2 nm Doppler broadened spectral lines, resulting from charge exchange recombination interactions between beam neutral atoms and plasma ions, are performed to determine ion temperatures, and toroidal and poloidal rotation velocities. The diagnostics system comprises 32 viewing chords spanning a typical minor radius of 63 cm across the midplane, of which 16 spatial chords span 11 cm of the plasma edge just within the separatrix. A temporal resolution of 260 μs per time slice can be obtained as a result of using MCP phosphors with short decay times and fast camera readout electronics. Results from this system will be used in radial electric field comparisons with theory at the L-H transition and ion transport analysis. 6 refs., 3 figs

[en] We report the results of experiments on DIII-D where quasi steady-state H-mode plasma with low amplitude Edge Localized Modes (ELMs) were maintained for 5 seconds. Within one second from the onset of the H-mode, most plasma parameters reach their asymptotic values (/bar n//sub e/ ∼ 7 /times/ 10¹³ cm/sup /minus/3/, /tau//sub E/ ≅ 100 ms, Z/sub eff/ = 1.7) and the electron density and temperature profiles are no longer evolving. By this time, frequent ELMs and effective helium wall conditioning limit the rate of increase of /bar n//sub e/ (≤10% of the beam fueling rate) and maintain the total radiated power form impurities at a constant level. 5 refs., 2 figs

[en] Doppler-shift spectroscopy has shown that finite values of poloidal rotation velocity υ_θ and of radial electric field E_r exist at the edge of a tokamak plasma and that dramatic increases occur in these parameters at an L-H transition. E_r is negative in the L-mode and becomes more negative in the H-mode; υ_θ increases in magnitude at the transition. In addition, the radial gradients (shear) of υ_θ and E_r are large and these gradients also increase at the L-H transition. These results are based on measurements of Doppler shifts of light emitted by He II ions, located in a region about 1--3 cm inside the separatrix. These observations have been made with horizontally-viewing and vertically-viewing spectrometer systems on the DIII-D tokamak. The nearly orthogonal views of these systems are used to determine the plasma's flow velocity in terms of the orthogonal sets υ_θ and υ_φ or of υ_{perpendicular} and υ_parallel. Knowledge of υ_{perpendicular} is used to calculate E_r from the force balance equation for a single ion species. The existing results impose constraints on theories of the L-H transition. More detailed studies of the spatial profiles and temporal evolution of υ_θ and E_r will be made with upgraded instrumentation, which is now coming on-line. 28 refs

[en] Much recent theoretical and experimental work has focused on the mechanisms controlling the transition from L-mode to H-mode and the subsequent improvement in transport and confinement. Measurements of the radial electric field, E_r, with high spatial and time resolution at the L-H transition have led to an understanding of the improved confinement of the plasma edge in H-mode plasmas based on the stabilization of plasma turbulence by sheared ExB flow. The radial electric field just inside the last closed flux surface (LCFS) changes dramatically at the L-H transition and a well-like structure in E_r forms simultaneously at the transition. At present, there is no accepted theory which gives the spatial structure of E_r near the plasma edge and which can predict its time evolution. Present theories propose mechanisms for the generation of a negative E_r at the L-H transition, the bifurcation conditions for the transition and the stabilization of turbulence by sheared ExB flow. Although the various theories invoke different mechanisms to derive the negative E_r (e.g., ion orbit losses, Stringer spin-up, nonlinear transport theory, self-regulating turbulence, they have as yet to come into full agreement with the observed experimental results and, in particular, the observed behavior of the poloidal rotation and pressure gradient of the main ions at the transition. Furthermore, these theories need to be extended to explain the formation of the spatial structure of E_r at the transition and its temporal development into the H-mode. In order to help development of theories on the E_r profile, we have examined the dependence of the radial profile of E_r on different plasma parameters

[en] An experimental technique is presented that permits diagnostics viewing light from the plasma edge to be spatially calibrated relative to one another. By sweeping the plasma edge, each chord of each diagnostic sweeps out a portion of the light emission profile. A nonlinear least-squares fit to such data provides superior cross-calibration of diagnostics located at different toroidal locations compared with simple surveying. Another advantage of the technique is that it can be used to monitor the position of viewing chords during an experimental campaign to ensure that alignment does not change over time. Moreover, should such a change occur, the data can still be cross-calibrated and its usefulness retained

[en] The goal of this paper is to present detailed measurements of T_i and E_r at the plasma edge in L- and H-mode with high spatial resolution in order the study the edge ion dynamics. Of primary interest is the relationship between T_i and E_r and the behavior of the edge T_i profile in H-mode. The principle findings are: there appears to be a threshold temperature for T_i required for the transition to occur with T_i at the LCFS in the range of 0.2--0.3 keV at the transition; a correlation between the edge E_r profile and the edge T_i profile has been observed; and values of T_i of 2--3 keV within a few cm of the LCFS and of dT_i/dr of up to 1 keV/cm are observed in the transport barrier in H-mode, with the scale length for T_i being of the order of a poloidal gyroradius

[en] Charge Exchange Recombination (CER) spectroscopy has become a standard diagnostic for tokamaks. CER measurements have been used to determine spatially and temporally resolved ion temperature, toroidal and poloidal ion rotation speed, impurity density and radial electric field. Knowledge of the spatial profile and temporal evolution of the electric field shear in the plasma edge is crucial to understanding the physics of the L to H transition. High speed CER measurements are also valuable for Edge Localized Mode (ELM) studies. Since the 0.52 ms minimum time resolution of our present system is barely adequate to study the time evolution of these phenomena, we have developed a new CCD detector system with about a factor of two better time resolution. In addition, our existing system detects sufficient photons to utilize the shortest time resolution only under exceptional conditions. The new CCD detector has a quantum efficiency of about 0.65, which is a factor of 7 better than our previous image intensifier-silicon photodiode detector systems. We have also equipped the new system with spectrometers of lower f/number. This combination should allow more routine operation at the minimum integration time, as well as improving data quality for measurements in the divertor-relevant region outside of the separatrix. Construction details, benchmark data and initial tokamak measurements for the new system will be presented

[en] A novel approach has been implemented on DIII-D to allow the correct determination of the plasma poloidal velocity from charge exchange spectroscopy measurements. Unlike usual techniques, the need for detailed atomic physics calculations to properly interpret the results is alleviated. Instead, the needed atomic physics corrections are self-consistently determined directly from the measurements, by making use of specially chosen viewing chords. Modeling results are presented that were used to determine a set of views capable of measuring the correction terms. We present the analysis of a quiescent H-mode discharge, illustrating that significant modifications to the velocity profiles are required in these high ion temperature conditions. We also present preliminary measurements providing the first direct comparison of the standard cross-section correction to the atomic physics calculations

[en] We report the results of experiments on DIII-D where quasi steady-state H-mode plasmas with low amplitude Edge Localized Modes (ELMs) were maintained for 5 seconds. Within one second from the onset of the H-mode, most plasma parameters reach their asymptotic values (n_e∼7.10₁₃, τ_E≅100 ms, Z_eff = 1.7) and the electron density and temperature profiles are no longer evolving. By this time, frequent ELMs and effective helium wall conditioning limit the rate of increase of n_e (<10% of the beam fueling rate) and maintain the total power from impurities at a constant level. (author) 5 refs., 2 figs

[en] Neutralization of a fast negative-ion beam, primarily H^-, is discussed in terms of competing one- and two-electron detachment processes in a variety of media: gas (vapor), plasma, liquid sheet, solid foil