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Journal Articles

ITER test blanket module error field simulation experiments at DIII-D

Schaffer, M. J.*; Snipes, J. A.*; Gohil, P.*; de Vries, P.*; Evans, T. E.*; Fenstermacher, M. E.*; Gao, X.*; Garofalo, A. M.*; Gates, D. A.*; Greenfield, C. M.*; et al.

Nuclear Fusion, 51(10), p.103028_1 - 103028_11, 2011/10

 Times Cited Count:32 Percentile:15.37(Physics, Fluids & Plasmas)

Experiments at DIII-D investigated the effects of ferromagnetic error fields similar to those expected from proposed ITER Test Blanket Modules (TBMs). Studied were effects on: plasma rotation and locking; confinement; L-H transition; edge localized mode (ELM) suppression by resonant magnetic perturbations; ELMs and the H-mode pedestal; energetic particle losses; and more. The experiments used a 3-coil mock-up of 2 magnetized ITER TBMs in one ITER equatorial port. The experiments did not reveal any effect likely to preclude ITER operations with a TBM-like error field. The largest effect was slowed plasma toroidal rotation v across the entire radial profile by as much as $$Delta v/v_{0} sim 50%$$ via non-resonant braking. Changes to global $$Delta n/n_{0}$$, $$Delta v/v_{0}$$ and $$Delta H_{98}/H_{98,0}$$ were $$sim$$3 times smaller. These effects are stronger at higher $$beta$$ and lower $$v_{0}$$. Other effects were smaller.

Journal Articles

Empirical scaling of sawtooth period for onset of neoclassical tearing modes

Chapman, I. T.*; Buttery, R. J.*; Coda, S.*; Gerhardt, S.*; Graves, J. P.*; Howell, D. F.*; Isayama, Akihiko; La Haye, R. J.*; Liu, Y.*; Maget, P.*; et al.

Nuclear Fusion, 50(10), p.102001_1 - 102001_7, 2010/10

 Times Cited Count:40 Percentile:13.38(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Plasma models for real-time control of advanced tokamak scenarios

Moreau, D.*; Mazon, D.*; Walker, M. L.*; Ferron, J. R.*; Flanagan, S. M.*; Gohil, P.*; Groebner, R. J.*; La Haye, R. J.*; Schuster, E.*; Ou, Y.*; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2010/10

Journal Articles

Prospects for stabilization of neoclassical tearing modes by electron cyclotron current drive in ITER

La Haye, R. J.*; Isayama, Akihiko; Maraschek, M.*

Nuclear Fusion, 49(4), p.045005_1 - 045005_8, 2009/04

 Times Cited Count:40 Percentile:14.15(Physics, Fluids & Plasmas)

no abstracts in English

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:690 Percentile:3.51(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:53 Percentile:11.53(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

Evaluating electron cyclotron current drive stabilization of neoclassical tearing modes in ITER; Implications of experiments in ASDEX upgrade, DIII-D, JET, and JT-60U

La Haye, R. J.*; Prater, R.*; Buttery, R. J.*; Hayashi, Nobuhiko; Isayama, Akihiko; Maraschek, M. E.*; Urso, L.*; Zohm, H.*

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

Resistive neoclassical tearing mode (NTM) islands will be the principal limit on stability and performance in ITER as beta is well below the ideal kink limit. NTM island control in ITER is predicted to be challenging both because of the relatively narrower marginal island widths and the relatively broader electron cyclotron current drive (ECCD). Measurements from ASDEX Upgrade, DIII-D, and JET in beta rampdown experiments are used to determine the marginal island size for m/n=3/2 NTM removal. This is compared to data from ASDEX Upgrade, DIII-D and JT-60U with elimination of the m/n=3/2 island by continuous ECCD at near constant beta. The empirical marginal island size is consistent in both sets of removal experiments and found to be about twice the ion banana width. A common methodology is developed for fitting the saturated m/n=3/2 island before (or without) ECCD in all four experimental devices. To this is added (and model tested to experiments) the effect of unmodulated co-ECCD on island stabilization including both replacing the missing bootstrap current and making the classical tearing stability index more negative. The experimentally benchmarked model is then used to evaluate ITER. The ITER ECCD upper launcher with up to 20 MW of injected power is appraised with or without modulation for both the m/n=3/2 mode and the m/n=2/1 NTM (which can lock to the resistive wall and induce disruption). An m/n=2/1 rotating island model with drag from eddy current induced in the resistive wall is used to predict the necessary ECCD to keep the island from locking as a function of the rotation in ITER. The planned relatively wide ECCD should be capable of regulating the island width to avoid mode locking with the anticipated rotation in ITER but there is little margin available for inevitable misalignment. Narrower ECCD of more power and/or more rotation in ITER would increase confidence in island control and successful operation.

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

Cross-machine benchmarking for ITER of neoclassical tearing mode stabilization by electron cyclotron current drive

La Haye, R. J.*; Prater, R.*; Buttery, R. J.*; Hayashi, Nobuhiko; Isayama, Akihiko; Maraschek, M. E.*; Urso, L.*; Zohm, H.*

Nuclear Fusion, 46(4), p.451 - 461, 2006/04

 Times Cited Count:131 Percentile:2.15(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

The Physics base for NTM stabilization by ECCD in ITER

Zohm, H.*; Hayashi, Nobuhiko; La Haye, R. J.*; Isayama, Akihiko; Maraschek, M. E.*; Sauter, O.*; Urso, L.*

Proceedings of 14th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating (EC-14), p.334 - 339, 2006/00

no abstracts in English

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:37.75(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.

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

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