Showing papers by "R.D. Stambaugh published in 1995"
TL;DR: In this article, a regime of improved H mode energy confinement, the VH mode, was obtained following boronization of the DIII-D Tokamak vacuum vessel.
Abstract: A regime of improved H mode energy confinement, the VH mode, was obtained following boronization of the DIII-D Tokamak vacuum vessel. The gradual confinement improvement in VH mode is associated with expansion of the H mode pedestal and reduction of thermal diffusivity in a region just inside the pedestal. Disappearance of density fluctuation bursts is associated with a confinement improvement in the latter region. The VH mode is terminated in a rapid global energy loss which is initiated by a mode with toroidal mode number, n approximately 5, consistent with calculated instability to an edge localized ideal kink. The improved confinement in VH mode is consistent with the extension of the region of the E*B velocity shear turbulence suppression zone further in from the plasma boundary. Expansion of the ideal ballooning second stability region and of the region with drift reversal stabilization of trapped particle modes are also considered as possible explanations for the confinement improvement
47 citations
TL;DR: The Radiative Divertor for DIII-D as mentioned in this paper is a double-null slot divertor with four cryopumps to provide particle control and neutral shielding for high-triangularity advanced tokamak discharges.
Abstract: DIII-D currently operates with a single- or double-null open divertor and graphite walls. Active particle control with a divertor cryopump has demonstrated density control, efficient helium exhaust, and reduction of the inventory of particles in the wall. Gas puffing of D{sub 2} and impurities has demonstrated reduction of the peak divertor beat flux by factors of 3--5 by radiation. A combination of active cryopumping and feedback-controlled D{sub 2} gas puffing has produced similar divertor heat flux reduction with density control. Experiments with neon puffing have shown that the radiation is equally-divided between a localized zone near the X-point and a mantle around the plasma core. The density in these experiments has also been controlled with cryopumping. These experimental results combined with modeling were used to develop the new Radiative Divertor for DIII-D. This is a double-null slot divertor with four cryopumps to provide particle control and neutral shielding for high-triangularity advanced tokamak discharges. UEDGE and DEGAS simulations, benchmarked to experimental data, have been used to optimize the design.
39 citations
TL;DR: A summary of recent DIII-D divertor physics activity and plans for future divertor upgrades can be found in this paper, where the divertor heat flux control by means of D 2 gas puffing and impurity injection were studied separately and in both cases up to a factor of five reduction of the diveror peak heat flux was observed.
37 citations
TL;DR: In this article, the authors used experiments and modeling to develop a new radiative divertor configuration for DIII-D. Gas puffing experiments with the existing open divertor have shown the creation of a localized (∼ 10 cm diameter) radiation zone which results in substantial reduction (3-10) in the divertor heat flux while τ E remains ∼ 2 times ITER-89P scaling.
29 citations
TL;DR: In this article, a particle exhaust scheme, employing a cryocondensation pump in the outboard divertor region under a baffle, has been installed and operated in the DIII-D tokamak.
Abstract: A particle exhaust scheme, employing a cryocondensation pump in the outboard divertor region under a baffle, has been installed and operated in the DIII-D tokamak. The cryopump provides toroidally symmetric pumping at a rate of 30000 to 40000 l/s for D{sub 2} in the pressure range of 1 to 4 mTorr. Pressures in the 2 to 3 mTorr range are routinely observed under the baffle. This translates to particle exhaust throughputs of nearly 100 Torr l/s. The exhaust throughput could be controlled by selecting the position of the plasma strike region with respect to the opening to the baffle chamber. The pump has been used quite effectively for plasma density control. 19 refs., 9 figs., 1 tab.
12 citations
TL;DR: In this article, the authors examined a denser and broader scrape-off layer (SOL) plasma, one class of which was first seen in VH mode, in the DIII-D tokamak.
6 citations