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in creator/contributor: "RHODES, T.L."

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ATF (Advanced Toroidal Facility) edge plasma turbulence studies using a fast reciprocating Langmuir probe

Electrostatic turbulence on the edge of the Advanced Torodial Facility (ATF) torsatron is investigated experimentally with a fast reciprocating Langmuir probe (FRLP) array. Initial measurements of plasma electron density n{sub e} and temperature T{sub e} and fluctuations in density ({tilde n}{sub e}) and plasma floating potential ({tilde {phi}}{sub f}) are made in ECH plasmas at 1 T. At the last closed flux surface (LCFS, r/{bar a} {approximately}1), T{sub e} {approx} 20--40 eV and n{sub e} {ap… more

Date: January 1, 1990

Creator: Uckan, T.; Hidalgo, C.; Bell, J. D.; Harris, J. H.; Dunlap, J. L.; Dyer, G. R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Edge turbulence and transport: Text and ATF modeling

We present experimental results on edge turbulence and transport from the tokamak TEXT and the torsatron ATF. The measured electrostatic fluctuations can explain the edge transport of particles and energy. Certain drive (radiation) and stabilizing (velocity shear) terms are suggested by the results. The experimental fluctuation levels and spectral widths can be reproduced by considering the nonlinear evolution of the reduced MHD equations, incorporating a thermal drive from line radiation. In t… more

Date: January 1, 1990

Creator: Ritz, C. P.; Rhodes, T. L.; Lin, H.; Rowan, W. L.; Bengtson, R.; Wootton, A. J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Physics of the L-mode to H-mode transition in tokamaks

Combined theoretical and experimental work has resulted in the creation of a paradigm which has allowed semi-quantitative understanding of the edge confinement improvement that occurs in the H-mode. Shear in the E {times} B flow of the fluctuations in the plasma edge can lead to decorrelation of the fluctuations, decreased radial correlation lengths and reduced turbulent transport. Changes in the radial electric field, the density fluctuations and the edge transport consistent with shear stabil… more

Date: July 1, 1992

Creator: Burrell, K. H.; Carlstrom, T. N.; Gohil, P.; Groebner, R. J.; Kim, J.; Osborne, T. H. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Physics of the L-mode to H-mode transition in tokamaks

Date: July 1, 1992

Creator: Burrell, K. H.; Carlstrom, T. N.; Gohil, P.; Groebner, R. J.; Kim, J.; Osborne, T. H. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Optimization of negative central shear discharges in shaped cross sections

Magnetohydrodynamic (MHD) stability analyses of Negative Central Shear (NCS) equilibria have revealed a new understanding of the limiting MHD instabilities in NCS experiments. Ideal stability calculations show a synergistic effect between cross section shape and pressure profile optimization; strong shaping and broader pressure independently lead to moderately higher {Beta} limits, but broadening of the pressure profile in a strongly dee-shaped cross- section leads to a dramatic increase in the… more

Date: October 1, 1996

Creator: Turnbull, A.D., Chu, M.S., Taylor, T.S., Casper, T.A., Rice, B.W.; Greene, J.M., Greenfield, C.M., La Haye, R.J., Lao, L.L., Lee, B.J.; Miller, R.L., Ren, C., Strait, E.J., Tritz, K.; Rettig, C.L., Rhodes, T.L. & Sauter, O.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Study of the phase transition dynamics of the L to H transition

A highly radiating zone (MARFE) just above the divertor X-point has been used to access the marginal transition regime P{sub sep} {approx} P{sub thres} to study the existence of a critical point for the L to H transition. Phase transition models predict that at the critical point, the transition duration increases and the plasma parameters vary continuously between L-mode and H-mode. In these experiments, the L to H transition duration increased 50--100 times over fast transitions. However, the… more

Date: September 1, 1997

Creator: Moyer, R. A.; Rhodes, T. L. & Rettig, C. L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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A Comparison of Plasma Performance Between Single-Null and Double-Null Configurations During Elming H-Mode

Tokamak plasma performance generally improves with increased shaping of the plasma cross section, such as higher elongation and higher triangularity. The stronger shaping, especially higher triangularity, leads to changes in the magnetic topology of the divertor. Because there are engineering and divertor physics issues associated with changes in the details of the divertor flux geometry, especially as the configuration transitions from a single-null (SN) divertor to a marginally balanced doubl… more

Date: July 1, 1999

Creator: Petrie, T. W.; Fenstermacher, M. E.; Allen, S. L.; Carlstrom, T. N.; Gohil, P.; Groebner, R. J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Studies of H-Mode Plasmas Produced Directly by Pellet Injection in the DIII-D Tokamak

A key issue for the physics of H-mode plasmas is to determine which plasma quantities are critical for the formation of the edge transport barrier. One approach is to directly perturb the edge plasma and observe the subsequent changes. In DIII-D, pellet injection has been used to directly change the edge plasma conditions and produce H-mode transitions. One hypothesis for the H-mode transition is that the attainment of a critical edge electron temperature is required for the transition [1-3]. T… more

Date: August 1, 2000

Creator: Gohil, P.; Baylor, L. R.; Jernigan, T. C.; Burrell, K. H.; Carlstrom, T. N.; McKee, G. R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Turbulent Radial Correlation Lengths in the DIII-D Tokamak

Measurements of the radial correlation length Ar of density fluctuations have been made on the DIII-D tokamak in a variety of L-mode discharges. These measurements span the radial region 0.5 < {rho} < 1 and are found to scale approximately as {rho}{sub {theta},s} or 5-10 {rho}{sub s}. Here {rho}{sub {theta},s} is the poloidal ion Larmor radius calculated using local T{sub e} and poloidal magnetic field and {rho}{sub s} is the same except calculated using the total magnetic field. The {Del… more

Date: August 1, 2000

Creator: Rhodes, T. L.; Leboeuf, J. N.; Sydora, R.; Doyle, E. J.; Moyer, R. A.; Rettig, C. L. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Long-Pulse, High-Performance Discharges in the DIII-D Tokamak

Significant progress in obtaining high performance discharges for many energy confinement times in the DIII-D tokamak has been realized since the previous IAEA meeting. In relation to previous discharges, normalized performance {approx}10 has been sustained for >5 {tau}{sub E} with q{sub min} >1.5. (The normalized performance is measured by the product {beta}{sub N} H{sub 89} indicating the proximity to the conventional {beta} limits and energy confinement quality, respectively.) These H-… more

Date: October 1, 2000

Creator: Luce, T. C.; Wade, M. R.; Politzer, P. A.; Allen, S. L.; Austin, M. E.; Baker, D. R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Progress in Quantifying the Edge Physics of H-Mode Regime in Diii-D

Edge conditions in DIII-D are being quantified in order to provide insight into the physics of the H-mode regime. Electron temperature is not the key parameter that controls the L-H transition. Gradients of edge temperature and pressure are much more promising candidates for such parameters. The quality of H-mode confinement is strongly correlated with the height of the H-mode pedestal for the pressure. The gradient of the pressure appears to be controlled by MHD modes, in particular by kink-ba… more

Date: October 1, 2000

Creator: Groebner, R. J.; Baker, D. R.; Boedo, J. A.; Burrell, K. H.; Carlstrom, T. N.; Deranian, R. D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Quiescent Double Barrier H-Mode Plasmas in the Diii-D Tokamak

High confinement (H-mode) operation is the choice for next-step tokamak devices based either on conventional or advanced tokamak physics. This choice, however, comes at a significant cost for both the conventional and advanced tokamaks because of the effects of edge localized modes (ELMs). ELMs can produce significant erosion in the divertor and can affect the beta limit and reduced core transport regions needed for advanced tokamak operation. Experimental results from DIII-D [J.L. Luxon, et al… more

Date: November 1, 2000

Creator: Burrell, K. H.; Austin, M. E.; Brennan, D. P.; Deboo, J. C.; Doyle, E. J.; Fenzi, C. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Quiescent Double Barrier H-Mode Plasmas in the DIII-D Tokamak

Date: November 1, 2000

Creator: Burrell, K. H.; Austin, M. E.; Brennan, D. P.; DeBoo, J. C.; Doyle, E. J.; Fenzi, C. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Mechanisms for Electron Transport Barrier Formation in the Diii-D Tokamak

The E x B shear stabilization paradigm explains much of the phenomenology of ion thermal transport in tokamaks. Behavior in the electron channel, however, has continued to challenge our understanding. Recent experiments in DIII-D and elsewhere produce regions where electron thermal transport is almost completely eliminated with intense, localized, direct electron heating. Simulations of DIII-D discharges identify {alpha}-stabilization, local magnetic shear stabilization due to the Shafranov shi… more

Date: February 1, 2001

Creator: Greenfield, C. M.; Prater, R.; Staebler, G. M.; Kinsey, J. E.; Burrell, K. H.; Boo, J. C. De et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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DIII-D Quiescent Double Barrier Regime Experiments and Modeling

Discharges characteristic of the quiescent double barrier (QDB) regime [1] are attractive for development of advanced tokamak (AT) scenarios relevant to fusion reactors [2] and they offer near term advantages for exploring and developing control techniques. We continue to explore the QDB regime in DIII-D to improve understanding of formation and control of these discharges and to explore scaling to steady-state reactors. The formation of an internal transport barrier (ITB) provides a naturally … more

Date: July 1, 2002

Creator: Casper, T. A.; Burrell, K. H.; DeBoo, J. C.; Doyle, E. J.; Gohil, P.; Greenfield, C. M. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Effect of the B Drift Direction on Plasma Edge Properties and the L-H Transition in DIII-D

The power threshold for the L-H transition, P{sub TH}, is low when the ion {del}B drift is toward the X-point and increases significantly when it is away from the X-point. In order to study the cause of this effect, we have compared lower single-null (LSN) discharges with upper single-null (USN) discharges where the ion {del}B drift direction is down in both cases. Since many plasma parameters change with input power, we have made comparisons at the same power level (PTOT=2.3 MW). For these exp… more

Date: July 1, 2002

Creator: Carlstrom, T. N.; Groebner, R. J.; McKee, G. R.; Moyer, R. A.; Rhodes, T. L.; Rost, J. C. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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TRANSPORT STUDIES IN DIII-D WITH MODULATED ECH

Experiments have been performed where the T{sub e} profile stiffness was tested at several spatial locations by varying the ECH resonance location. Propagation of the pulses was Fourier analyzed and compared to simulations based on several transport models. The plasma appears to be near the critical T{sub e} gradient for ETG modes and marginally stable to ITG modes. However, the local T{sub e} response to a locally applied heat pulse does not indicate a nonlinear, critical gradient model where … more

Date: July 1, 2002

Creator: DeBoo, J. C.; Austin, M. E.; Bravenec, R. V.; Kinsey, J. E.; Lohr, J.; Luce, T. C. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Recent Experimental Studies of Edge and Internal Transport Barriers in the Diii-D Tokamak

Results from recent experiments on the DIII-D tokamak have revealed many important details on transport barriers at the plasma edge and in the plasma core. These experiments include: (a) the formation of the H-mode edge barrier directly by pellet injection; (b) the formation of a quiescent H-mode edge barrier (QH-mode) which is free from edge localized modes (ELMs), but which still exhibits good density and radiative power control; (c) the formation of multiple transport barriers, such as the q… more

Date: August 1, 2002

Creator: Gohil, P.; Baylor, L. R.; Burrell, K. H.; Casper, T. A.; Doyle, E. J.; Greenfield, C. M. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Simulations of Boundary Turbulence in Tokamak Experiments

Comparisons between the boundary plasma turbulence observed in the BOUT code and experiments on C-Mod, NSTX, and DIII-D are presented. BOUT is a 3D non-local electromagnetic turbulence simulation code which models boundary-plasma turbulence in a realistic divertor geometry using the modified Braginskii equations for plasma vorticity, density, the electron and ion temperatures and parallel momenta. Many features of the Quasi-Coherent (QC) mode, observed at high densities during enhanced D-alpha … more

Date: October 11, 2002

Creator: Nevins, W. M.; Xu, X. Q.; Carlstrom, T. N.; Cohen, R. H.; Groebner, R.; Jennings, T. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Current Drive and Pressure Profile Modifications with Electron Cyclotron Power in DIII-D Quiescent Double Barrier Experiments

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Date: June 30, 2003

Creator: Casper, T. A.; Burrell, K. H.; Doyle, E. J.; Gohil, P.; Greenfield, C. M.; Groebner, R. J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Current Drive and Pressure Profile Modification with Electron Cyclotron Power in DIII-D Quiescent Double Barrier Experiments

OAK-B135 High confinement mode (H-mode) operation is a leading scenario for burning plasma devices due to its inherently high energy-confinement characteristics. The quiescent H-mode (QH-mode) offers these same advantages with the additional attraction of more steady edge conditions where the highly transient power loads due to edge localized mode (ELM) activity is replaced by the steadier power and particle losses associated with an edge harmonic oscillation (EHO). With the addition of an inte… more

Date: July 1, 2003

Creator: Casper, T. A.; Burrell, K. H.; Doyle, E. J.; Gohil, P.; Greenfield, C. M.; Groebner, R. J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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DIII-D Experiments and Modeling of Core Confinement in Quiescent Double Barrier Plasmas

We continue to explore Quiescent Double Barrier (QDB) operation on DIII-D to address issues of critical importance to internal transport barrier (ITB) plasmas. QDB plasmas exhibit both a core transport barrier and a quiescent, H-mode edge barrier. Both experiments and modeling of these plasmas are leading to an increased understanding of this regime and it's potential advantages for advanced-tokamak (AT) burning-plasma operation. These near steady plasma conditions have been maintained on DIII-… more

Date: October 24, 2003

Creator: Jayakumar, J.; Casper, T. A.; Lasnier, C. J.; Burrell, K. H.; Doyle, E. J.; Gohil, P. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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OBSERVATION OF MHD INSTABILITY AND DIRECT MEASUREMENT OF LOCAL PERTURBED MAGNETIC FIELD USING MOTIONAL STARK EFFECT DIAGNOSTIC

OAK-B135 The local oscillating component of the poloidal magnetic field in plasma associated with MHD instabilities has been measured using the motional Stark effect (MSE) diagnostic on the DIII-D tokamak. The magnetic field perturbations associated with a resistive wall mode (RWM) rotated by internal coils at 20 Hz was measured using the conventional MSE operation mode. These first observations of perturbations due to a MHD mode were obtained on multiple MSE channels covering a significant por… more

Date: November 1, 2003

Creator: JAYAKUMAR,RJ; Makowski, M. A.; Allen, S. L.; Austin, M.E.; Garofalo, A. M.; La Haye, R. J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Suppression of Large Edge Localized Modes in High Confinement DIII-D Plasmas With a Stochastic Magnetic Boundary

OAK-B135 A stochastic magnetic boundary, produced by an externally applied edge resonant magnetic perturbation, is used to suppress large edge localized modes (ELMs) in high confinement (H-mode) plasmas. The resulting H-mode displays rapid, small oscillations with a bursty character modulated by a coherent 130 Hz envelope. The H-mode transport barrier is unaffected by the stochastic boundary. The core confinement of these discharges is unaffected, despite a three-fold drop in the toroidal rotat… more

Date: November 1, 2003

Creator: Evans, T. E.; Moyer, R. A.; Thomas, P. R.; Watkins, J. G.; Osborne, T. H.; Boedo, J. A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department