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Experimental measurements and modeling of impurity transport in the divertor and boundary plasma of DIII-D

Description: Analysis of trace impurity injection experiments on DIII-D during a beam power scan is presented. Spectroscopic measu- rements indicate that as beam power is increased, and concomitantly ELM frequency and scrape-off-layer thickness increase while energy confinement decreases, the core impurity content decreases only slightly. Modeling of the edge plasma using the UEDGE 2D and NEWT1D plasma fluid codes indicate that as beam power is increased, the parallel forces on an impurity ion increase in t… more
Date: July 1, 1994
Creator: West, W. P.; Brooks, N. H. & Allen, S. L.
Partner: UNT Libraries Government Documents Department
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Atomic Physics Processes Important to the Understanding of the Scrape-Off Layer of Tokamaks

Description: The region between the well-confined plasma and the vessel walls of a magnetic confinement fusion research device, the scrape-off layer (SOL), is typically rich in atomic and molecular physics processes. The most advanced magnetic confinement device, the magnetically diverted tokamak, uses a magnetic separatrix to isolate the confinement zone (closed flux surfaces) from the edge plasma (open field lines). Over most of their length the open field lines run parallel to the separatrix, forming a t… more
Date: May 1, 2002
Creator: West, W. P.; Goldsmith, B.; Evans, T. E. & Olson, R. J.
Partner: UNT Libraries Government Documents Department
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Impurity penetration and transport during VH-mode on DIII-D

Description: A new modeling effort is made in order to understand the observed relatively low levels of impurity contamination during the VH-mode phase on DIII-D, as compared to those observed during the H-mode phase of selected discharges. The key element is the inclusion of the real 2-D flux surface geometry in the prediction of impurity penetration of sputtered atoms through the scrape-off layer into the core plasma. Of the elements which determine the impurity content in the plasma: sputtering yield, pe… more
Date: May 1, 1992
Creator: Lippmann, S. I.; Evans, T. E.; Jackson, G. L. & West, W. P.
Partner: UNT Libraries Government Documents Department
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Impurity penetration and transport during VH-mode on DIII-D

Description: A new modeling effort is made in order to understand the observed relatively low levels of impurity contamination during the VH-mode phase on DIII-D, as compared to those observed during the H-mode phase of selected discharges. The key element is the inclusion of the real 2-D flux surface geometry in the prediction of impurity penetration of sputtered atoms through the scrape-off layer into the core plasma. Of the elements which determine the impurity content in the plasma: sputtering yield, pe… more
Date: May 1, 1992
Creator: Lippmann, S. I.; Evans, T. E.; Jackson, G. L. & West, W. P.
Partner: UNT Libraries Government Documents Department
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Modeling of impurity spectroscopy in the divertor and SOL of DIII-D using the 1D multifluid model NEWT1D

Description: NEWT1D, a one dimensional multifluid model of the scrape-off layer and divertor plasma, has been used to model the plasma including the distribution of carbon ionization states in the SOL and divertor of ELMing H-mode at two injected power levels in DIII-D. Comparison of the code predictions to the measured divertor and scrape-off layer (SOL) plasma density and temperature shows good agreement. Comparison of the predicted line emissions to the spectroscopic data suggests that physically sputter… more
Date: October 1, 1996
Creator: West, W. P.; Evans, T. E. & Brooks, N. H.
Partner: UNT Libraries Government Documents Department
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Divertor Plasma Studies on DIII-D: Experiment and Modeling

Description: In a magnetically diverted tokamak, the scrape-off layer (SOL) and divertor plasma provides separation between the first wall and the core plasma, intercepting impurities generated at the wall before they reach the core plasma. The divertor plasma can also serve to spread the heat and particle flux over a large area of divertor structure wall using impurity radiation and neutral charge exchange, thus reducing peak heat and particle fluxes at the divertor strike plate. Such a reduction will be r… more
Date: September 1996
Creator: West, W. P.; Brooks, N. H. & Allen, S. L.
Partner: UNT Libraries Government Documents Department
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Carbon influx in He and D plasmas in DIII-D

Description: Differences in the carbon behavior between He and D plasmas during VH-mode, L-mode and L-mode with excess gas puffing are reported and inferences on the importance of the various carbon sources during these modes of operation are discussed. During a VH-mode phase, VUV and visible charge exchange spectroscopy indicates that for both He and D operation the carbon behavior is very similar. In the edge plasma, carbon build up is quite rapid, and the carbon influx represents a large fraction of the … more
Date: July 1998
Creator: West, W. P.; Brooks, N. H. & Fenstermacher, M. E.
Partner: UNT Libraries Government Documents Department
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Impurity enrichment and radiative enhancement using induced SOL flow in DIII-D

Description: Experiments on DIII-D have demonstrated the efficacy of using induced scrap-off-layer (SOL) flow to preferentially enrich impurities in the divertor plasma. This SOL floe is produced through simultaneous deuterium gas injection at the midplane and divertor exhaust. Using this SOL flow, an improvement in enrichment (defined as the ratio of impurity fraction in the divertor to that in the plasma core) has been observed for all impurities in trace-level experiments (i.e., impurity level is non-per… more
Date: July 1998
Creator: Wade, M. R.; West, W. P. & Wood, R. D.
Partner: UNT Libraries Government Documents Department
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Magnetic pitch angle measurements on text using laser-enhanced attenuation of a Li beam

Description: The polarization of the {pi} component of the Zeeman split Li2P-2S transition allows a direct spectroscopic measurement of the local magnetic pitch angle. Li atoms are injected radially into TEXT as a 95 keV beam, and the intensity of the transmitted beam is detected. A polarization-modulated, cavity-dumped dye laser, tuned into resonance with the {pi} line, is injected collinearly with the beam. Laser excitation of the beam results in an enhanced beam attenuation. Time-resolved detection of th… more
Date: September 1, 1990
Creator: West, W. P.; McChesney, J.; Thomas, M. K. & Yang, X. Z.
Partner: UNT Libraries Government Documents Department
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Hydrogen isotope retention in B{sub 4}C coating on RGT graphite under high heat fluxes of DIII-D divertor plasma

Description: The results of the investigation of retention and thermal desorption of hydrogen isotopes of B{sub 4}C coated RGT (a recrystallized graphite with high thermal conductivity, 600 W/mK) after the exposure to high heat flux in the divertor strike point region of DIII-D using the DiMES sample exchange system are reported. It is shown that the material is very promising for plasma facing elements of tokamaks.
Date: November 1, 1997
Creator: Opimach, I. V.; Buzhinskij, O. I.; West, W. P. & Wampler, W.
Partner: UNT Libraries Government Documents Department
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Characterization of Core Impurity Transport and Accumulation in Various Operating Regimes in DIII-D

Description: Impurity contaminants in the core plasma of future burning devices such as the International Thermonuclear Experimental Reactor (ITER) are inevitable and will undoubtedly have a deleterious effect on plasma performance. Unfortunately, because of the limited amount of information available, the models presently being used to predict ITER performance simply assume a flat concentration profile for all impurities with an ad hoc concentration chosen for each impurity. In an attempt to start closing … more
Date: July 1, 1996
Creator: Wade, M. R.; Whyte, D. G.; Wood, R. D. & West, W. P.
Partner: UNT Libraries Government Documents Department
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Suppression of erosion in the DIII-D divertor with detached plasmas

Description: The ability to withstand disruptions makes carbon-based materials attractive for use as plasma-facing components in divertors. However, such materials suffer high erosion rates during attached plasma operation which, in high power long pulse machines, would give short component lifetimes and high tritium inventories. The authors present results from recent experiments in DIII-D, in which the Divertor Materials Evaluation System (DiMES) was used to examine erosion and deposition during short exp… more
Date: May 25, 2000
Creator: Wampler, William R.; Bastasz, Robert J.; Whyte, D. G.; Wong, C. P. C. & West, W. P.
Partner: UNT Libraries Government Documents Department
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Surface impurity removal from DIII-D graphite tiles by boron carbide grit blasting

Description: During the latter half of 1992, the DIII-D tokamak at General Atomics (GA) underwent several modifications of its interior. One of the major tasks involved the removal of accumulated metallic impurities from the surface of the graphite tiles used to line the plasma facing surfaces inside of the tokamak. Approximately 1500 graphite tiles and 100 boron nitride tiles from the tokamak were cleaned to remove the metallic impurities. The cleaning process consisted of several steps: the removed graphi… more
Date: November 1, 1993
Creator: Lee, R. L.; Hollerbach, M. A.; Holtrop, K. L.; Kellman, A. G.; Taylor, P. L. & West, W. P.
Partner: UNT Libraries Government Documents Department
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Divertor materials evaluation system (DiMES)

Description: The mission of the Divertor Materials Evaluation System (DiMES) in DIII-D is to establish an integrated data base from measurements in the divertor of a tokamak in order to address some of the ITER and fusion power reactor plasma material interaction issues. Carbon and metal coatings of Be, W, V, and Mo were exposed to the steady-state outer strike point on DIII-D for 4--18 s. These short exposure times ensure controlled exposure conditions, and the extensive arrays of DIII-D divertor diagnosti… more
Date: December 1997
Creator: Wong, C. P. C.; West, W. P.; Whyte, D. G.; Bastasz, R. J.; Brooks, J. & Wampler, W. R.
Partner: UNT Libraries Government Documents Department
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Stability of a radiative mantle in ITER

Description: We report results of a study to evaluate the efficacy of various impurities for heat dispersal by a radiative mantle and radiative divertor(including SOL). We have derived a stability criterion for the mantle radiation which favors low Z impurities and low ratios of edge to core thermal conductivities. Since on the other hand the relative strength of boundary line radiation to core bremsstrahlung favors high Z impurities, we find that for the ITER physics phase argon is the best gaseous impurit… more
Date: December 1, 1996
Creator: Mahdavi, M. A.; Staebler, G. M.; Wood, R. D.; Whyte, D. G. & West, W. P.
Partner: UNT Libraries Government Documents Department
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QUIESCENT H-MODE, AN ELM-FREE HIGH-CONFINEMENT MODE ON DIII-D WITH POTENTIAL FOR STATIONARY STATE OPERATION

Description: OAK-B135 The quiescent H-mode (QH-mode) is an ELM-free and stationary state mode of operation discovered on DIII-D. This mode achieves H-mode levels of confinement and pedestal pressure while maintaining constant density and radiated power. The elimination of edge localized modes (ELMs) and their large divertor loads while maintaining good confinement and good density control is of interest to next generation tokamaks. This paper reports on the correlations found between selected parameters in … more
Date: August 1, 2003
Creator: West, W. P.; Burrell, K. H.; Degrassie, J. S.; Doyle, E. J.; Greenfield, C. M.; Lasnier, C. J. et al.
Partner: UNT Libraries Government Documents Department
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Particle Flows in Pumped DIII-D Discharges

Description: The dynamics of particle flows in the DIII-D tokamak for two divertor configurations is considered. Fuel and intrinsic carbon impurity flows are analyzed using experimental data and 2D fluid plasma simulations. The flows in puff and pump experiments done in an open and a closed divertor geometry are described. It is shown that the flow of fuel particles is sensitive to divertor geometry. The pumping efficiency of the DIII-D cryopumps is a factor of 2 higher in a closed geometry than an open. Th… more
Date: May 17, 2000
Creator: Porter, G. D.; Rognlien, T. D.; Rensink, M. E.; Wolf, N. & West, W. P.
Partner: UNT Libraries Government Documents Department
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Erosion results from DiMES and design implications to ITER and Starlite

Description: Using the DiMES mechanism at DIII-D, erosion rates of graphite, and metallic coatings of Be, V, Mo, and W have been measured under different plasma operating conditions. The measured net erosion rate for C is substantial (16 nm/s) during ELMing H-mode at a heat flux of 2 MW/m{sup 2}. Measured gross erosion rates of the metals are lower than expected from sputtering yields, most likely due to heavy surface contamination by carbon. The measured erosion of W is substantially lower than the other m… more
Date: July 1996
Creator: Wong, C. P. C.; West, W. P.; Bastaz, R. J.; Whyte, D. G. & Wampler, W. R.
Partner: UNT Libraries Government Documents Department
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Effects of particle fueling and plasma wall interactions on DIII-D discharges

Description: DIII-D has successfully operated with an all-graphite first wall, including the first observations of VH-mode without boronization. A major goal of this, and other recent upgrades, was to control impurity influxes and hydrogenic fueling. Graphite tiles were carefully pre-conditioned, first by ex situ preparation and then by baking and helium glow conditioning. No deuterium or hydrogen was used until tokamak operation commenced. With the all graphite wall, both impurity and deuterium influxes du… more
Date: November 1, 1994
Creator: Jackson, G. L.; Baker, D. R.; Holtrop, K. L.; Staebler, G. M.; West, W. P.; Maingi, R. et al.
Partner: UNT Libraries Government Documents Department
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High Performance Plasma Operation on DIII-D During Extended Periods Without Boronization

Description: High performance plasmas, including both hybrid and advanced tokamak (AT) bench-mark discharges, were shown to be highly repeatable in DIII-D over 6000 plasma-seconds of operation during the 2006 campaign with no intervening boron depositions or high temperature bakes. Hybrid and AT discharges with identical control targets were repeated after the initial boronization at the beginning of the 2006 campaign, and again just before and after a second boronization near the end of the 2006 campaign. … more
Date: June 27, 2007
Creator: West, W. P.; Groth, M.; Hyatt, A. W.; Jackson, G. L.; Wade, M. R.; Greenfield, C. M. et al.
Partner: UNT Libraries Government Documents Department
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Multi-fluid code simulations including anomalous non-diffusive transport of plasma and impurities in the tokamak SOL

Description: Fast intermittent transport has been observed in the scrape-off layer (SOL) of major tokamaks including Alcator C-Mod, DIII-D, and NSTX. This kind of transport is not diffusive but rather convective. It strongly increases plasma flux to the chamber walls and enhances the recycling of neutral particles in the main chamber. We discuss anomalous cross-field convection (ACFC) model for impurity and main plasma ions and its relation to intermittent transport events, i.e. plasma density blobs and hol… more
Date: November 25, 2003
Creator: Pigarov, A. Yu; West, W. P.; Soukhanovskii, V.; Rognlien, T. D.; Maingi, R.; Lipschultz, B. et al.
Partner: UNT Libraries Government Documents Department
open access

Divertor Materials Evaluation System (DiMES)

Description: The mission of the Divertor Materials Evaluation System (DiMES) in DIII-D is to establish an integrated data base from measurements in the divertor of a tokamak in order to address some of the ITER and fusion power reactor plasma material interaction issues. Carbon and metal coatings of Be, W, V, and Mo were exposed to the steady-state outer strike point on DIII-D for 4-18 s. These short exposure times ensure controlled exposure conditions, and the extensive arrays of DIII-D divertor diagnostic… more
Date: November 1997
Creator: Wong, C. P.; West, W. P.; Whyte, D. G.; Bastasz, R. J.; Brooks, J. & Wampler, W. R.
Partner: UNT Libraries Government Documents Department
open access

First measurements of the ion energy distribution at the divertor strike point during DIII-D disruptions

Description: Plasma disruptions are a serious concern in tokamak design because of the high impulsive heat loads which can cause strong erosion of divertor materials due to enhanced sputtering, or melting/ablation in the most severe cases. Predictions of net erosion rates and hence component lifetimes are very difficult and are highly dependent on the plasma conditions over the divertor target. It is therefore necessary to characterize the properties of the scrape-off plasma near the divertor target plate u… more
Date: March 1996
Creator: Parks, P. B.; Brooks, N. H.; West, W. P.; Wong, C. P. C.; Bastasz, R.; Wampler, W. R. et al.
Partner: UNT Libraries Government Documents Department
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