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Non-linear instability of DIII-D to error fields

Description: Otherwise stable DIII-D discharges can become nonlinearly unstable to locked modes and disrupt when subjected to resonant m = 2, n = 1 error field caused by irregular poloidal field coils, i.e. intrinsic field errors. Instability is observed in DIII-D when the magnitude of the radial component of the m = 2, n = 1 error field with respect to the toroidal field is B{sub r21}/B{sub T} of about 1.7 {times} 10{sup {minus}4}. The locked modes triggered by an external error field are aligned with the … more
Date: October 1, 1991
Creator: La Haye, R. J. & Scoville, J. T.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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An X-point ergodic divertor

Description: A new ergodic divertor is proposed. It utilizes a system of external (n = 3) coils arranged to generate overlapping magnetic islands in the edge region of a diverted tokamak and connect the randomized field lines to the external (cold) divertor plate. The novel feature in the configuration is the placement of the external coils close to the X-point. A realistic design of the external coil set is studied by using the field line tracing method for a low aspect ratio (A {approx equal} 3) tokamak. … more
Date: October 1, 1991
Creator: Chu, M. S.; Jensen, T. H.; La Haye, R. J.; Taylor, T. S. & Evans, T. E.
Item Type: Refine your search to only Article
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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Limits on m = 2, n = 1 error field induced locked mode instability in TPX with typical sources of poloidal field coil error field and a prototype correction coil, C-coil''

Description: Irregularities in the winding or alignment of poloidal or toroidal magnetic field coils in tokamaks produce resonant low m, n = 1 static error fields. Otherwise stable discharges can become nonlinearly unstable, and locked modes can occur with subsequent disruption when subjected to modest m = 2, n = 1 external perturbations. Using both theory and the results of error field/locked mode experiments on DIII-D and other tokamaks, the critical m = 2, n = 1 applied error field for locked mode instab… more
Date: December 1, 1992
Creator: La Haye, R. J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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DIII-D research operations. Annual report, October 1, 1992--September 30, 1993

Description: The DIII-D tokamak research program is carried out by General Atomics (GA) for the U.S. Department of Energy (DOE). The DIII-D is the most flexible tokamak in the world. The primary goal of the DIII-D tokamak research program is to provide data to develop a conceptual physics blueprint for a commercially attractive electrical demonstration plant (DEMO) that would open a path to fusion power commercialization. In doing so, the DIII-D program provides physics and technology R&D outputs to aid the… more
Date: May 1, 1994
Creator: La Haye, R. J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Limits on m = 2, n = 1 error field induced locked mode instability in TPX with typical sources of poloidal field coil error field and a prototype correction coil, ``C-coil``

Description: Irregularities in the winding or alignment of poloidal or toroidal magnetic field coils in tokamaks produce resonant low m, n = 1 static error fields. Otherwise stable discharges can become nonlinearly unstable, and locked modes can occur with subsequent disruption when subjected to modest m = 2, n = 1 external perturbations. Using both theory and the results of error field/locked mode experiments on DIII-D and other tokamaks, the critical m = 2, n = 1 applied error field for locked mode instab… more
Date: December 1, 1992
Creator: La Haye, R. J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Relationship Between Onset Thresholds, Trigger Types, and Rotation Shear for the m/n=2/1 Neoclassical Tearing Mode in a High-β Spherical Torus

Description: The onset conditions for the m/n=2/1 neoclassical tearing mode (NTM) are studied in terms of neoclassical drive, triggering instabilities, and toroidal rotation or rotation shear, in the spherical torus NSTX [M. Ono, et al., Nuclear Fusion 40, 557 (2000)]. There are three typical onset conditions for these modes, given in order of increasing neoclassical drive required for mode onset: triggering by energetic particle modes, triggering by edge localized modes, and cases where the modes appear to… more
Date: February 24, 2009
Creator: Gerhardt, S. P.; Brennan, D. P.; Buttery, R.; La Haye, R. J.; Sabbagh, S.; Strait, E. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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CONTROL OF MHD STABILITY IN DIII-D ADVANCED TOKAMAK DISCHARGES

Description: OAK-B135 Advanced tokamak research in DIII-D seeks to optimize the tokamak approach for fusion energy production, leading to a compact, steady state power source. High power density implies operation at high toroidal beta, {beta}{sub T}=<p>2{micro}{sub 0}/B{sub T}{sup 2}, since fusion power density increases roughly as the square of the plasma pressure. Steady-state operation with low recirculating power for current drive implies operation at high poloidal beta, {beta}{sub P} = <p>2… more
Date: June 1, 2003
Creator: Strait, E. J.; Bialek, J.; Chance, M. S.; Chu, M. S.; Edgell, D. H.; Ferron, J. R. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Complete Suppression of the M/N=2/1 Neoclassical Tearing Mode Using Radially Localized Electron Cyclotron Current Drive on Diii-D and the Requirements for Iter

Description: OAK-B135 DIII-D experiments demonstrate the first real-time feedback control of the relative location of a narrow beam of microwaves to completely suppress and eliminate a growing tearing mode at the q=2 surface. long wavelength tearing modes such as the m/n = 2/1 instability are particularly deleterious to tokamak operation. Confinement is seriously degraded by the island, plasma rotation can cease (mode-lock) and disruption can occur. The neoclassical tearing mode (NTM) becomes unstable due t… more
Date: June 1, 2003
Creator: La Haye, R. J.; Luce, T. C.; Petty, C. C.; Humphreys, D. A.; Hyatt, A. W.; Perkins, F. W. et al.
Item Type: Refine your search to only 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

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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Control of Neoclassical Tearing Modes in Diii-D

Description: The development of techniques for neoclassical tearing mode (NTM) suppression or avoidance is crucial for successful high beta/high confinement tokamaks. Neoclassical tearing modes are islands destabilized and maintained by a helically perturbed bootstrap current and represent a significant limit to performance at higher poloidal beta. The confinement-degrading islands can be reduced or completely suppressed by precisely replacing the ''missing'' bootstrap current in the island O-point or by in… more
Date: November 1, 2001
Creator: La Haye, R. J.; Gunter, S.; Humphreys, D. A.; Lohr, J.; Luce, T. C.; Maraschek, M. E. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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SUSTAINED STABILIZATION OF THE RESISTIVE WALL MODE BY PLASMA ROTATION IN THE DIII-D TOKAMAK

Description: OAK-B135 A path to sustained stable operation, at plasma pressure up to twice the ideal magnetohydrodynamic (MHD) n = 1 free-boundary pressure limit, has been discovered in the DIII-D tokamak. Tuning the correction of the intrinsic magnetic field asymmetries so as to minimize plasma rotation decay during the high beta phase and increasing the angular momentum injection, have allowed maintaining the plasma rotation above that needed for stabilization of the resistive wall mode (RWM). A new metho… more
Date: October 1, 2001
Creator: Garofalo, A. M.; Strait, E. J.; Johnson, L. C.; La Haye, R. J.; Lazarus, E. A; Navratil, G. A. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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STABILZATION OF NEOCLASSICAL TEARING MODES BY LOCALIZED ECCD IN DIII-D

Description: Neoclassical tearing modes (NTMs) are MHD modes which can become destabilized in a tokamak by a helical pressure perturbation. The NTM is particularly well suited to control since the mode is linearly stable although nonlinearly unstable, so if the island amplitude can be decreased below a threshold size the mode will decay and vanish. One means of shrinking the island is the replacement of the ''missing'' bootstrap current by a localized current generated by electron cyclotron current drive (E… more
Date: May 1, 2002
Creator: Prater, R.; Eliss, R. A., III; La Haye, R. J.; Lohr, J. M.; Luce, T. C.; Perkins, F. W. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Role of core toroidal rotation shear on turbulence and transport in the improved confinement regimes of the DIII-D tokamak

Description: This a brief report which discusses the role of core toroidal rotation shear on turbulence and transport in the improved confinement regimes of the doublet-3 tokamak.
Date: August 1, 1993
Creator: La Haye, R. J.; Greenfield, C. M.; Groebner, R. J.; Hyatt, A. W.; Lao, L. L.; 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 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.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Neoclassical tearing modes in DIII-D and calculations of the stabilizing effects of localized electron cyclotron current drive

Description: Neoclassical tearing modes are found to limit the achievable beta in many high performance discharges in DIII-D. Electron cyclotron current drive within the magnetic islands formed as the tearing mode grows has been proposed as a means of stabilizing these modes or reducing their amplitude, thereby increasing the beta limit by a factor around 1.5. Some experimental success has been obtained previously on Asdex-U. Here the authors examine the parameter range in DIII-C in which this effect can be… more
Date: May 1, 1999
Creator: Prater, R.; La Haye, R. J.; Lin-Liu, Y. R.; Lohr, J.; Bernabei, S.; Perkins, F. W. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Physics of locked modes in ITER: Error field limits, rotation for obviation, and measurement of field errors

Description: The existing theoretical and experimental basis for predicting the levels of resonant static error field at different components m,n that stop plasma rotation and produce a locked mode is reviewed. For ITER ohmic discharges, the slow rotation of the very large plasma is predicted to incur a locked mode (and subsequent disastrous large magnetic islands) at a simultaneous weighted error field ({Sigma}{sub 1}{sup 3}w{sub m1}B{sup 2}{sub rm1}){sup {1/2}}/B{sub T} {ge} 1.9 x 10{sup -5}. Here the wei… more
Date: February 1, 1997
Creator: La Haye, R. J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Wall stabilization of high beta plasmas in DIII-D

Description: Detailed analysis of recent high beta discharges in the DIII-D tokamak demonstrates that the resistive vacuum vessel can provide stabilization of low n magnetohydrodynamic (MHD) modes. The experimental beta values reaching up to {beta}{sub T} = 12.6% are more than 30% larger than the maximum stable beta calculated with no wall stabilization. Plasma rotation is essential for stabilization. When the plasma rotation slows sufficiently, unstable modes with the characteristics of the predicted {open… more
Date: February 1, 1995
Creator: Taylor, T. S.; Strait, E. J.; Lao, L. L.; Turnbull, A. D.; Burrell, K. H.; Chu, M. S. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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