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Journal Articles

Dynamics of energetic particle driven modes and MHD modes in wall-stabilized high-$$beta$$ plasmas on JT-60U and DIII-D

Matsunaga, Go; Okabayashi, Michio*; Aiba, Nobuyuki; Boedo, J. A.*; Ferron, J. R.*; Hanson, J. M.*; Hao, G. Z.*; Heidbrink, W. W.*; Holcomb, C. T.*; In, Y.*; et al.

Nuclear Fusion, 53(12), p.123022_1 - 123022_13, 2013/12

 Times Cited Count:2 Percentile:10.4(Physics, Fluids & Plasmas)

Journal Articles

Dynamics of energetic particle driven modes and MHD modes in wall-stabilized high beta plasmas on JT-60U and DIII-D

Matsunaga, Go; Okabayashi, Michio*; Aiba, Nobuyuki; Boedo, J. A.*; Ferron, J. R.*; Hanson, J. M.*; Hao, G. Z.*; Heidbrink, W. W.*; Holcomb, C. T.*; In, Y.*; et al.

Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2013/03

Journal Articles

Progress in the ITER physics basis, 3; MHD stability, operational limits and disruptions

Hender, T. C.*; Wesley, J. C.*; Bialek, J.*; Bondeson, A.*; Boozer, A. H.*; Buttery, R. J.*; Garofalo, A.*; Goodman, T. P.*; Granetz, R. S.*; Gribov, Y.*; et al.

Nuclear Fusion, 47(6), p.S128 - S202, 2007/06

 Times Cited Count:759 Percentile:98.25(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Stabilization and prevention of the 2/1 neoclassical tearing mode for improved performance in DIII-D

Prater, R.*; La Haye, R. J.*; Luce, T. C.*; Petty, C. C.*; Strait, E. J.*; Ferron, J. R.*; Humphreys, D. A.*; Isayama, Akihiko; Lohr, J.*; Nagasaki, Kazunobu*; et al.

Nuclear Fusion, 47(5), p.371 - 377, 2007/05

 Times Cited Count:56 Percentile:88.64(Physics, Fluids & Plasmas)

The $$m=2$$ /$$n=1$$ neoclassical tearing mode (NTM) has been observed to strongly degrade confinement and frequently lead to a disruption in high $$beta$$ discharges in DIII-D if allowed to grow to large size. Stabilization of grown NTMs by application of highly localized electron cyclotron current drive (ECCD) at the island location has led to operation at increased plasma pressure, up to the no-wall kink limit. After the NTM is stabilized by the ECCD, the correct location for the current drive is maintained using information from real-time equilibrium reconstructions which include measurements from the motional Stark effect diagnostic. This same process is used alternatively to prevent the mode from ever growing, leading to performance at the pressure limit in high performance hybrid discharges with $$beta$$ above 4%. Modeling using the modified Rutherford equation shows that the required power is in close agreement with the experimental threshold for prevention of the 2/1 NTM.

Journal Articles

Prevention of the 2/1 neoclassical tearing mode in DIII-D

Prater, R.*; La Haye, R. J.*; Luce, T. C.*; Petty, C. C.*; Strait, E. J.*; Ferron, J. R.*; Humphreys, D. A.*; Isayama, Akihiko; Lohr, J.*; Nagasaki, Kazunobu*; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

Onset of the m/n=2/1 neoclassical tearing mode (NTM) has been prevented in high-performance DIII-D discharges using localized electron cyclotron current drive (ECCD). Active tracking of the $$q$$=2 surface location, using real-time equilibrium reconstructions with motional Stark effect data, allows the current drive to be maintained at the rational surface even in the absence of a detectable mode. With the application of this technique in DIII-D hybrid discharges, the 2/1 mode is avoided and good energy confinement is maintained for more than 1 second with $$beta$$ at the estimated n=1 no-wall stability limit for ideal kink modes ($$beta$$$$_{rm T}$$ approximately equals 3.9 % and normalized beta $$beta$$$$_{rm N}$$ approximately equals 3.2). The results can be understood through modeling using the modified Rutherford equation.

Journal Articles

MHD limits to tokamak operation and their control

Zohm, H.*; Gantenbein, G.*; Isayama, Akihiko; Keller, A.*; La Haye, R. J.*; Maraschek, M.*; M$"u$ck, A.*; Nagasaki, Kazunobu*; Pinches, S. D.*; Strait, E. J.*

Plasma Physics and Controlled Fusion, 45(12A), p.A163 - A173, 2003/12

 Times Cited Count:24 Percentile:60.93(Physics, Fluids & Plasmas)

A review of magnetohydrodynamic limits to tokamak operation in terms of current, density and pressure is given. Although the current and density limits in a tokamak usually lead to disruptive termination of the discharge, it is argued that these can be avoided by staying away from the respective limits. This is especially true since operation close to these limits is not really desirable, due to the decreased confinement at very high density and the high disruptivity at low q. On the other hand, the limit to plasma pressure set by neoclassical tearing modes (NTMs) and resistive wall modes (RWMs) is too low to guarantee economic operation of future fusion reactors. Therefore, active control of these two instabilities is now being studied. Noticeable progress has been made by NTM stabilization with ECCD. Avoidance of NTMs and RWMs by tailoring sawteeth and spinning the plasma, shows promising results. Also, experiments on direct RWM stabilization by active coils are showing their first encouraging results.

Journal Articles

Reduction of recycling in DIII-D by degassing and conditioning of the graphite tiles

Jackson, G. L.*; Taylor, T. S.*; Allen, S. L.*; Ferron, J.*; Haas, G.*; Hill, D.*; Mahdavi, M. A.*; Nakamura, Hiroo; Osborne, T. H.*; Petersen, P. I.*; et al.

Journal of Nuclear Materials, 162-164, p.489 - 495, 1989/04

 Times Cited Count:26 Percentile:91.47(Materials Science, Multidisciplinary)

no abstracts in English

Oral presentation

Extrapolating neoclassical tearing mode physics to ITER

Buttery, R. J.*; La Haye, R. J.*; Coda, S.*; Gohil, P.*; Isayama, Akihiko; Jackson, G.*; Raju, D.*; Reimerdes, H.*; Sabbagh, S.*; Sen, A.*; et al.

no journal, , 

no abstracts in English

Oral presentation

Dynamics of MHD modes in high-$$beta$$ tokamak plasmas

Matsunaga, Go; Okabayashi, Michio*; Aiba, Nobuyuki; Boedo, J. A.*; Ferron, J. R.*; Hanson, J. M.*; Hao, G. Z.*; Heidbrink, W. W.*; Holcomb, C. T.*; In, Y.*; et al.

no journal, , 

no abstracts in English

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