Measurement of the Resistive-Wall-Mode Stability in a Rotating Plasma Using Active MHD Spectroscopy

Reimerdes, H.; Chu, M. S.; Garofalo, A. M.; Jackson, G.L.; Haye, R.J. La; Navratil, G.A.; Okabayashi, M.; Scoville, J.T.; Strait, E. J.

doi:10.1103/physrevlett.93.135002

Cited by 96 publications

(100 citation statements)

References 15 publications

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“…Similar results have also been obtained on DIII-D [26]. Further, these results are consistent with lowfrequency MHD spectroscopy measurements [27] indicating the presence of a stable n = 1 RWM resonant at 30-50 Hz in the co-rotation direction [28] as shown in figure 7.…”

Section: Macroscopic Stabilitysupporting

confidence: 89%

Overview of recent physics results from the National Spherical Torus Experiment (NSTX)

Ménard¹,

Bell²,

Bell³

et al. 2007

Nucl. Fusion

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The National Spherical Torus Experiment (NSTX) has made considerable progress in advancing the scientific understanding of high performance long-pulse plasmas needed for future spherical torus (ST) devices and ITER. Plasma durations up to 1.6 s (five current redistribution times) have been achieved at plasma currents of 0.7 MA with non-inductive current fractions above 65% while simultaneously achieving β T and β N values of 17% and 5.7 (%m T MA −1 ), respectively. A newly available motional Stark effect diagnostic has enabled validation of currentdrive sources and improved the understanding of NSTX 'hybrid'-like scenarios. In MHD research, ex-vessel radial field coils have been utilized to infer and correct intrinsic EFs, provide rotation control and actively stabilize the n = 1 resistive wall mode at ITER-relevant low plasma rotation values. In transport and turbulence research, the low aspect ratio and a wide range of achievable β in the NSTX provide unique data for confinement scaling studies, and a new microwave scattering diagnostic is being used to investigate turbulent density fluctuations with wavenumbers extending from ion to electron gyro-scales. In energetic particle research, cyclic neutron rate drops have been associated with the destabilization of multiple large toroidal Alfven eigenmodes (TAEs) analogous to the 'sea-of-TAE' modes predicted for ITER, and three-wave coupling processes have been observed for the first time. In boundary physics research, advanced shape control has enabled studies of the role of magnetic balance in H-mode access and edge localized mode stability. Peak divertor heat flux has been reduced by a factor of 5 using an H-mode-compatible radiative divertor, and lithium conditioning has demonstrated particle pumping and results in improved thermal confinement. Finally, non-solenoidal plasma start-up experiments have achieved plasma currents of 160 kA on closed magnetic flux surfaces utilizing coaxial helicity injection.

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Section: Macroscopic Stabilitysupporting

confidence: 89%

Overview of recent physics results from the National Spherical Torus Experiment (NSTX)

Ménard¹,

Bell²,

Bell³

et al. 2007

Nucl. Fusion

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“…25,26 The response to a static perturbation and the response to a dynamic perturbation are related. 27 These considerations predicted the existence of very low frequency plasma resonances and are observed in the plasma very low frequency experiments of Reimerdes et al 28 Next the effect of flow on feedback for this set of equilibria is analyzed. The results are shown in the following two figures.…”

Section: Feedback Stabilization Of the Rwm In A Rotating Plasmamentioning

confidence: 88%

Modeling of feedback and rotation stabilization of the resistive wall mode in tokamaks

et al. 2004

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Steady-state operation of the advanced tokamak reactor relies on maintaining plasma stability with respect to the resistive wall mode (RWM). Active magnetic feedback and plasma rotation are the two methods proposed and demonstrated for this purpose. A comprehensive modeling effort including both magnetic feedback and plasma rotation is needed for understanding the physical mechanisms of the stabilization and to project to future devices. For plasma with low rotation, a complete solution for the feedback issue is obtained by assuming the plasma obey ideal magnetohydrodynamics (MHDs) and utilizing a normal mode approach (NMA) [M.S. Chu, et al., Nucl. Fusion 43, 441 (2003)]. It is found that poloidal sensors are more effective than radial sensors and coils inside of the vacuum vessel more effective than outside. For plasmas with non-negligible rotation, a comprehensive linear non-ideal MHD code, the MARS-F has been found to be suitable. MARS-F [Y.Q. Liu, et al., Phys. Plasmas 7, 3681 (2000)] has been benchmarked in the ideal MHD limit against the NMA. Effect of rotation stabilization of the plasma depends on the plasma dissipation model. Broad qualitative features of the experiment are reproduced. Rotation reduces the feedback gain required for RWM stabilization. Reduction is significant when rotation is near the critical rotation speed needed for stabilization. International Thermonuclear Experimental Reactor (ITER) [R. Aymar, et al., Plasma Phys. Control. Fusion 44, 519 (2002)] (scenario IV for advanced tokamak operation) may be feedback stabilized with β above the no wall limit and up to an increment of ~50% towards the ideal limit. Rotation further improves the stability.

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“…The slow toroidal rotation of the external field, which is negligible with respect to any of the plasma frequencies shown in Fig. 2, allows for coherent detection of the n ¼ 1 plasma response [19]. Measurements of the perturbed radial magnetic field with a toroidal array of saddle loops at the outboard midplane, shown in Fig.…”

mentioning

confidence: 99%

Evidence for the Importance of Trapped Particle Resonances for Resistive Wall Mode Stability in High Beta Tokamak Plasmas

et al. 2011

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Active measurements of the plasma stability in tokamak plasmas reveal the importance of kinetic resonances for resistive wall mode stability. The rotation dependence of the magnetic plasma response to externally applied quasistatic n=1 magnetic fields clearly shows the signatures of an interaction between the resistive wall mode and the precession and bounce motions of trapped thermal ions, as predicted by a perturbative model of plasma stability including kinetic effects. The identification of the stabilization mechanism is an essential step towards quantitative predictions for the prospects of "passive" resistive wall mode stabilization, i.e., without the use of an "active" feedback system, in fusion-alpha heated plasmas.

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Measurement of the Resistive-Wall-Mode Stability in a Rotating Plasma Using Active MHD Spectroscopy

Cited by 96 publications

References 15 publications

Overview of recent physics results from the National Spherical Torus Experiment (NSTX)

Overview of recent physics results from the National Spherical Torus Experiment (NSTX)

Modeling of feedback and rotation stabilization of the resistive wall mode in tokamaks

Evidence for the Importance of Trapped Particle Resonances for Resistive Wall Mode Stability in High Beta Tokamak Plasmas

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