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in creator/contributor: "Rhodes, T L"  
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Physics of the L-mode to H-mode transition in tokamaks

Description: 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.
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Partner: UNT Libraries Government Documents Department
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DIII-D Experiments and Modeling of Core Confinement in Quiescent Double Barrier Plasmas

Description: 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.
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Partner: UNT Libraries Government Documents Department
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Suppression of Large Edge Localized Modes with a Stochastic Magnetic Boundary in High Confinement DIII-D Plasmas

Description: Large sub-millisecond heat pulses due to Type-I ELMs have been reproducibly eliminated in DIII-D for periods approaching 7 energy confinement times with small dc currents driven in a simple magnetic perturbation coil. The current required to eliminate all but a few isolated Type-I ELM impulses during a perturbation coil pulse lasting several seconds is less than 0.4% of plasma current. Based on vacuum magnetic field line modeling, perturbation fields from the coil resonate strongly with plasma … more
Date: October 18, 2004
Creator: Evans, T. E.; Moyer, R. A.; Watkins, J. G.; Osborne, T. H.; Thomas, P. R.; Becoulet, M. et al.
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Partner: UNT Libraries Government Documents Department
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Quiescent Double Barrier H-Mode Plasmas in the DIII-D Tokamak

Description: 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 this year have dem… 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.
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Partner: UNT Libraries Government Documents Department
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Simulations of Boundary Turbulence in Tokamak Experiments

Description: 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: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

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

Description: 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: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Edge turbulence and transport: Text and ATF modeling

Description: 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.
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Partner: UNT Libraries Government Documents Department
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ATF (Advanced Toroidal Facility) edge plasma turbulence studies using a fast reciprocating Langmuir probe

Description: 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.
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Partner: UNT Libraries Government Documents Department
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Refractive and Relativistic Effects on ITER Low Field Side Reflectometer Design

Description: The ITER low field side reflectometer faces some unique design challenges, among which are included the effect of relativistic electron temperatures and refraction of probing waves. This paper utilizes GENRAY, a 3- D ray tracing code, to investigate these effects. Using a simulated ITER operating scenario, characteristics of the reflected RF waves returning to the launch plane are quantified as a function of a range of design parameters, including antenna height, antenna size, and antenna radia… more
Date: June 1, 2010
Creator: Wang, G.; Rhodes, T. L.; Peebles, W. A.; Harvey, R. W. & Budny, R. V.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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ELM Suppression in Low Edge Collisionality H-Mode Discharges Using n=3 Magnetic Perturbations

Description: Using resonant magnetic perturbations with toroidal mode number n = 3, we have produced H-mode discharges without edge localized modes (ELMs) which run with constant density and radiated power for periods up to about 2550 ms (17 energy confinement times). These ELM suppression results are achieved at pedestal collisionalities close to those desired for next step burning plasma experiments such as ITER and provide a means of eliminating the rapid erosion of divertor components in such machines w… more
Date: July 11, 2005
Creator: Burrell, K. H.; Evans, T. E.; Doyle, E. J.; Fenstermacher, M. E.; Groebner, R. J.; Leonard, A. W. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Edge Localized Mode Control in DIII-D Using Magnetic Perturbation-Induced Pedestal Transport Changes

Description: Edge localized mode (ELM) control is a critical issue for ITER because the impulsive power loading from ELMs is predicted to limit the divertor lifetime to only a few hundred full-length pulses. Consequently, a technique that replaces the ELM-induced transport with more continuous transport while preserving the H-mode pedestal height and core performance would significantly improve the viability of ITER. One approach is to use edge resonant magnetic perturbations (RMPs) to enhance pedestal tran… more
Date: September 27, 2006
Creator: Moyer, R. A.; Burrell, K. H.; Evans, T. E.; Fenstermacher, M. E.; Joseph, I.; Osborne, T. H. et al.
Item Type: Refine your search to only 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

Description: 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: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Observation of Energetic Particle Driven Modes Relevant to Advanced Tokamak Regimes

Description: Measurements of high-frequency oscillations in JET [Joint European Torus], JT-60U, Alcator C-Mod, DIII-D, and TFTR [Tokamak Fusion Test Reactor] plasmas are contributing to a new understanding of fast ion-driven instabilities relevant to Advanced Tokamak (AT) regimes. A model based on the transition from a cylindrical-like frequency-chirping mode to the Toroidal Alfven Eigenmode (TAE) has successfully encompassed many of the characteristics seen in experiments. In a surprising development, the … more
Date: October 21, 2004
Creator: Nazikian, R.; Alper, B.; Berk, H. L.; Borba, D.; Boswell, C.; Budny, R. V. et al.
Item Type: Refine your search to only Report
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

Description: 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: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Study of Aspect Ratio Effects on Kinetic MHD Instabilities in NSTX and DIII-D

Description: We report general observations of kinetic instabilities on the low aspect-ratio National Spherical Torus Experiment (NSTX) and describe explicit aspect ratio scaling studies of kinetic instabilities using both the NSTX and the DIII-D tokamak. The NSTX and the DIII-D tokamak are nearly ideal for such experiments, having a factor of two difference in major radius but otherwise similar parameters. We also introduce new theoretical work on the physics of kinetic ballooning modes (KBM), toroidal Alf… more
Date: October 21, 2004
Creator: Fredrickson, E. D.; Heidbrink, W. W.; Cheng, C. Z.; Gorelenkov, N. N.; Belova, E.; Hyatt, A. W. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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