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OVERVIEW OF RECENT EXPERIMENTAL RESULTS FROM THE DIII-D ADVANCED TOKAMAK PROGRAM

Description: OAK A271 OVERVIEW OF RECENT EXPERIMENTAL RESULTS FROM THE DIII-D ADVANCED TOKAMAK PROGRAM. The DIII-D research program is developing the scientific basis for advanced tokamak (AT) modes of operation in order to enhance the attractiveness of the tokamak as an energy producing system. Since the last International Atomic Energy Agency (IAEA) meeting, the authors have made significant progress in developing the building blocks needed for AT operation: (1) the authors have doubled the magnetohydrody… more
Date: November 1, 2002
Creator: BURRELL,KH
Partner: UNT Libraries Government Documents Department
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Summary of experimental progress and suggestions for future work

Description: Since the last H-mode workshop in 1991, there has been significant progress in a number of areas. In addition to H-modes in tokamaks, H-mode has been achieved in a current-free stellarator, a heliotron/torsatron with some net toroidal current and in a linear, tandem mirror. Because H-mode has been seen in a variety of magnetic confinement devices and has been produced by a variety of methods, a universal explanation is needed for the H-mode confinement improvement. The hypothesis of turbulence … more
Date: March 1, 1994
Creator: Burrell, K. H.
Partner: UNT Libraries Government Documents Department
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Flow shear induced fluctuation suppression in finite aspect ratio shaped tokamak plasma

Description: The suppression of turbulence by the E {times} B flow shear and parallel flow shear is studied in an arbitrary shape finite aspect ratio tokamak plasma using the two point nonlinear analysis previously utilized in a high aspect rat& tokamak plasma. The result shows that only the E {times} B flow shear is responsible for the suppression of flute-like fluctuations. This suppression occurs regardless of the plasma rotation direction and is therefore, relevant for the VH mode plasma core as well as… more
Date: January 1, 1995
Creator: Hahm, T. S. & Burrell, K. H.
Partner: UNT Libraries Government Documents Department
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Effects of ExB Velocity Shear and Magnetic Shear on Turbulence and Transport in Magnetic Confinement Devices

Description: One of the scientific success stories of fusion research over the past decade is the development of the ExB shear stabilization model to explain the formation of transport barriers in magnetic confinement devices. This model was originally developed to explain the transport barrier formed at the plasma edge in tokamaks after the L (low) to H (high) transition. This concept has the universality needed to explain the edge transport barriers seen in limiter and divertor tokamaks, stellarators, and… more
Date: November 1, 1996
Creator: Burrell, K. H.
Partner: UNT Libraries Government Documents Department
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Role of flow shear in enhanced core confinement regimes

Description: The importance of the ExB flow shear in various enhanced confinement regimes is discussed in terms of the turbulence suppression criterion in toroidal geometry. This criterion is then further generalized to include the poloidal angle dependence of the equilibrium electrostatic potential. The implication of the recently observed in-out asymmetry in the fluctuation behavior in DIII-D VH-mode is discussed.
Date: March 1, 1996
Creator: Hahm, T.S. & Burrell, K.H.
Partner: UNT Libraries Government Documents Department
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MODEL OF THE TOKAMAK EDGE DENSITY PEDESTAL INCLUDING DIFFUSIVE NEUTRALS

Description: OAK-B135 Several previous analytic models of the tokamak edge density pedestal have been based on diffusive transport of plasma plus free-streaming of neutrals. This latter neutral model includes only the effect of ionization and neglects charge exchange. The present work models the edge density pedestal using diffusive transport for both the plasma and the neutrals. In contrast to the free-streaming model, a diffusion model for the neutrals includes the effect of both charge exchange and ioniz… more
Date: January 1, 2003
Creator: BURRELL.KH
Partner: UNT Libraries Government Documents Department
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Enhanced confinement regimes and control technology in the DIII-D tokamak

Description: Advanced tokamak performance has been demonstrated in the DIII-D tokamak in a series of experiments which brought together developments in technology and improved understanding of the physical principles underlying tokamak operation. The achievement of greatly improved confinement coupled with development of new systems for real time plasma control have permitted investigation of the heretofore hidden or poorly controlled variables which together determine global confinement. These experiments,… more
Date: July 1, 1993
Creator: Lohr, J.; Burrell, K. H. & Coda, S.
Partner: UNT Libraries Government Documents Department
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Investigations of VH-mode in DIII-D and JET

Description: The VH-mode regime of high confinement has been observed in both DIII-D and JET. VH-mode is characterized by thermal confinement twice that seen in H-mode, with the edge transport barrier penetrating deeper into the plasma. Two mechanisms have been identified as important in achieving this high level of confinement. Expansion of the {rvec E} {times} {rvec B} velocity shear turbulence suppression zone is important in allowing reductions in local transport, while access to the second ballooning s… more
Date: September 1, 1993
Creator: Greenfield, C. M.; Burrell, K. H. & Balet, B.
Partner: UNT Libraries Government Documents Department
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A global fitting code for multichordal neutral beam spectroscopic data

Description: Knowledge of the heat deposition profile is crucial to all transport analysis of beam heated discharges. The heat deposition profile can be inferred from the fast ion birth profile which, in turn, is directly related to the loss of neutral atoms from the beam. This loss can be measured spectroscopically be the decrease in amplitude of spectral emissions from the beam as it penetrates the plasma. The spectra are complicated by the motional Stark effect which produces a manifold of nine bright pe… more
Date: May 1, 1992
Creator: Seraydarian, R.P.; Burrell, K.H. & Groebner, R.J.
Partner: UNT Libraries Government Documents Department
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Evidence for modified transport due to sheared E x B flows in high-temperature plasmas

Description: Sheared mass flows are generated in many fluids and are often important for the dynamics of instabilities in these fluids. Similarly, large values of the E x B velocity have been observed in magnetic confinement machines and there is theoretical and experimental evidence that sufficiently large shear in this velocity may stabilize important instabilities. Two examples of this phenomenon have been observed in the DIII-D tokamak. In the first example, sufficient heating power can lead to the L-H … more
Date: November 1, 1994
Creator: Groebner, R. J.; Burrell, K. H. & Austin, M. E.
Partner: UNT Libraries Government Documents Department
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A global fitting code for multichordal neutral beam spectroscopic data

Description: Knowledge of the heat deposition profile is crucial to all transport analysis of beam heated discharges. The heat deposition profile can be inferred from the fast ion birth profile which, in turn, is directly related to the loss of neutral atoms from the beam. This loss can be measured spectroscopically be the decrease in amplitude of spectral emissions from the beam as it penetrates the plasma. The spectra are complicated by the motional Stark effect which produces a manifold of nine bright pe… more
Date: May 1, 1992
Creator: Seraydarian, R. P.; Burrell, K. H. & Groebner, R. J.
Partner: UNT Libraries Government Documents Department
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Recent VH-Mode Results on DIII-D

Description: A regime of improved H-mode energy confinement, VH-mode, is obtained in the DIII-D tokamak with adequate vessel conditioning. The improved confinement in VH-mode is consistent with the extension of the region of high E {times} B velocity shear turbulence suppression zone further in from the plasma boundary. The energy confinement enhancement in VH-mode can be limited by ELMs, localized momentum transfer events, or operation at high heating power or low q. Energy confinement enhancement improves… more
Date: January 1, 1994
Creator: Osborne, T. H.; Burrell, K. H. & Carlstrom, T. N.
Partner: UNT Libraries Government Documents Department
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High performance low and high q discharges in DIII-D

Description: The High performance H-mode regime on DIII-D has been extended to both low q and high q (high {Beta}p) and low q operation. In high current operation, VH-mode discharges were obtained for the first time with I{sub P}(MA)/B{sub T} (T) > 1. These discharges had q{sub 95}= 3.4, H = 2.9, {Beta}{sub N}= 3, and {Beta}{sub T}{Tau}{sub E}=3%-sec. {Beta}{sub T}{Tau}{sub E} was improved by approximately 50% over previous results. These discharges were obtained with neutral beam injection during the plasm… more
Date: January 1, 1996
Creator: Osborne, T.H.; Burrell, K.H. & Chu, M.S.
Partner: UNT Libraries Government Documents Department
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Rotational and magnetic shear stabilization of magnetohydrodynamic modes and turbulence in DIII-D high performance discharges

Description: The confinement and the stability properties of the DIII-D tokamak high performance discharges are evaluated in terms of rotational and magnetic shear with emphasis on the recent experimental results obtained from the negative central magnetic shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside the NCS region accompanied by a reduction in core fluctuation amplitudes. Increasing negative magnetic shear contributes to the formation of this core tr… more
Date: August 1, 1996
Creator: Lao, L. L.; Burrell, K. H. & Casper, T. S.
Partner: UNT Libraries Government Documents Department
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Demonstration of high performance negative central magnetic shear discharges on the DIII-D tokamak

Description: Reliable operation of discharges with negative central magnetic shear has led to significant increases in plasma performance and reactivity in both low confinement, L-mode, and high confinement, H-mode, regimes in the DIII-D tokamak. Using neutral beam injection early in the initial current ramp, a large range of negative shear discharges have been produced with durations lasting up to 3.2 s. The total non- inductive current (beam plus bootstrap) ranges from 50% to 80% in these discharges. In t… more
Date: January 1, 1996
Creator: Rice, B. W.; Burrell, K. H. & Lao, L. L.
Partner: UNT Libraries Government Documents Department
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Dependence of H-mode power threshold on global and local edge parameters

Description: Measurements of local electron density n{sub e}, electron temperature T{sub e}, and ion temperature T{sub i} have been made at the very edge of the plasma just prior to the transition into H-mode for four different single parameter scans in the DIII-D tokamak. The means and standard derivations of n{sub e}, T{sub e}, and T{sub i} under these conditions for a value of the normalized toroidal flux of 0.98 are respectively, 1.5 {+-} 0.7 x 10{sup 19} m{sup -3}, 0.051 {+-} 0.016 keV, and 0.14 {+-} 0… more
Date: December 1, 1995
Creator: Groebner, R. J.; Carlstrom, T. N. & Burrell, K. H.
Partner: UNT Libraries Government Documents Department
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Confinement and stability of DIII-D negative central shear discharges

Description: Negative central magnetic shear (NCS) discharges with {Beta}{sub N} {le} 4, H {le} 3, and up to 80% of the current non-inductively driven are reproducibly produced in the DIII-D tokamak. Strong peaking of T{sub i}, plasma rotation, and in some cases n{sub e} are observed inside the NCS region. Transport analysis shows that the core ion thermal diffusivity is substantially reduced and near the neoclassical value after the formation of the internal transport barrier. The negative central shear is… more
Date: December 1, 1995
Creator: Lao, L. L.; Burrell, K. H. & Chan, V. S.
Partner: UNT Libraries Government Documents Department
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Sample system for time resolved tokamak plasma impurity analysis

Description: A fast sample system for time resolved measurements of material transport and unipolar arcing in ISX-B, located at Oak Ridge National Laboratory, has been designed, fabricated and tested. The sample system consists of a wheel which is driven through about one revolution during ISX plasma discharge. The wheel is driven via a cable and bellows system from outside the plasma chamber. A feedthrough mechanism supports and advances the fast sample system through an isolation valve to the exposure pos… more
Date: October 1, 1979
Creator: Hager, E. R.; Burrell, K. H.; Ellis, L. V.; Ahlgren, D. H. & Gomay, Y.
Partner: UNT Libraries Government Documents Department
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Plasma Rotation and the Radial Electric Field During Off-Axis NBI in the DIII-D Tokamak

Description: Experiments have been carried out on the DIII-D tokamak to investigate whether off-axis NBI can: (a) drive significant perpendicular flow to lead to increased suppression of turbulence and improved confinement, and (b) be used to control the radial electric field profile. Measurements of both impurity ion poloidal and toroidal rotation profiles were made using charge exchange recombination spectroscopy. These experiments used a low current, low elongation (I{sub p} = 0.5 MA, {kappa} = 1.2) plas… more
Date: December 1, 1995
Creator: Gohil, P.; Burrell, K. H.; Osborne, T. H. & Hassam, A. B.
Partner: UNT Libraries Government Documents Department
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Comparison of a {del}B drift effect model with measured H-mode power thresholds

Description: The H-mode power threshold has a weak but positive B{sub T} dependence when the ion {del}B drift is away from the X-point, in contrast to the nearly linear B{sub T} dependence when the ion {del}B drift is toward the X-point. This indicates that geometry plays an important role in the H-mode power threshold scaling. A simple model of the {del}B drift effect failed to predict this behavior, but successfully predicted the sign change of gas puffing and low X-point height on the power threshold. Th… more
Date: September 1, 1997
Creator: Carlstrom, T. N.; Burrell, K. H. & Groebner, R. J.
Partner: UNT Libraries Government Documents Department
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Plasma rotation and rf heating in DIII-D

Description: In a variety of discharge conditions on DIII-D it is observed that rf electron heating reduces the toroidal rotation speed and core ion temperature. The rf heating can be with either fast wave or electron cyclotron heating and this effect is insensitive to the details of the launched toroidal wavenumber spectrum. To date all target discharges have rotation first established with co-directed neutral beam injection. A possible cause is enhanced ion momentum and thermal diffusivity due to electron… more
Date: May 1, 1999
Creator: deGrassie, J. S.; Baker, D. R. & Burrell, K. H.
Partner: UNT Libraries Government Documents Department
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Results from the DIII-D scientific research program

Description: The DIII-D research program is aimed at developing the scientific basis for advanced modes of operation which can enhance the commercial attractiveness of the tokamak as an energy producing system. Features that improve the attractiveness of the tokamak as a fusion power plant include: high power density (which demands high {beta}), high ignition margin (high energy confinement time), and steady state operation with low recirculating power (high bootstrap fraction), as well as adequate divertor… more
Date: November 1998
Creator: Taylor, T. S.; Burrell, K. H. & Baker, D. R.
Partner: UNT Libraries Government Documents Department
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Study of H-Mode Threshold Conditions in DIII-D

Description: Studies have been conducted in DIII-D to determine the dependence of the power threshold P{sub lh} for the transition to the H-mode regime and the threshold P{sub hl} for the transition from H-mode to L-mode as functions of external parameters. There is a value of the line-averaged density n{sub e} at which P{sub lh} has a minimum and P{sub lh} tends to increase for lower and higher values of n{sub e}. Experiments conducted to separate the effect of the neutral density n{sub 0} from the plasma … more
Date: October 1996
Creator: Groebner, R. J.; Carlstrom, T. N. & Burrell, K. H.
Partner: UNT Libraries Government Documents Department
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