Investigation of resistive wall mode stabilization physics in high-beta plasmas using applied non-axisymmetric fields in NSTX*

Sontag, A. C.; Sabbagh, S. A.; Zhu, W.; Ménard, J.; Bell, R. E.; Bialek, J.; Bell, M.G.; Gates, D.; Glasser, A. H.; LeBlanc, B.; Shaing, K. C.; Stutman, D.; Tritz, K.

doi:10.1088/0029-5515/47/8/035

Cited by 57 publications

(134 citation statements)

References 30 publications

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“…The ratio, Φ w / Φ x w , is called Resonant Field Amplification (RFA) [10] in this paper, while ( Φ w / Φ x w ) − 1 is used in other articles [11][12][13][14]. The relation between S ↔ and (s E , α E ) can be expressed in terms of inductance coefficients and so-called the permeability of the plasma ↔ P .…”

Section: Relation Between Plasma Response and Rfa Measurementmentioning

confidence: 99%

“…So, three additional constraints are introduced in the fitting procedure, based on the previous observations for the peak of RFA in NSTX [12,13], and also based on the range in the measured RFA phases in Fig. 2 (b).…”

Section: Rfa Measurement In Nstx and Empirical Derivationmentioning

confidence: 99%

“…Magnetic perturbations are both amplified and phase shifted by the plasma response [10], as has been demonstrated in a number of Resonant Field Amplification (RFA) measurements [11][12][13][14]. The amplification and the phase shift by small perturbations are related to the perturbed energy and toroidal torque, which thus can be derived from magnetic measurements.…”

Section: Introductionmentioning

confidence: 95%

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Shielding of external magnetic perturbations by torque in rotating tokamak plasmas

et al. 2009

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The imposition of a nonaxisymmetric magnetic perturbation on a rotating tokamak plasma requires energy and toroidal torque. Fundamental electrodynamics implies that the torque is essentially limited and must be consistent with the external response of a plasma equilibrium f = j × B.Here magnetic measurements on National Spherical Torus eXperiment (NSTX) device are used to derive the energy and the torque, and these empirical evaluations are compared with theoretical calculations based on perturbed scalar pressure equilibria f = ∇p coupled with the theory of nonambipolar transport. The measurement and the theory are consistent within acceptable uncertainties, but can be largely inconsistent when the torque is comparable to the energy. This is expected since the currents associated with the torque are ignored in scalar pressure equilibria, but these currents tend to shield the perturbation.

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Section: Relation Between Plasma Response and Rfa Measurementmentioning

confidence: 99%

Section: Rfa Measurement In Nstx and Empirical Derivationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

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Shielding of external magnetic perturbations by torque in rotating tokamak plasmas

et al. 2009

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“…β N ∼ 5(%m T MA −1 ) is maintained for 3-4τ CR , and the plasma current flat-top is 1.6 s, an ST record at this current level. Previously long pulse discharges at high-β were limited by a slow degradation of rotation in the plasma core with the eventual onset of either a saturated internal kink mode [30] or an RWM [31]. The measured plasma rotation at various radii plotted versus time during a discharge that utilized combined n = 3 EF correction and n = 1 RFA suppression.…”

Section: Efs and Resonant Field Amplification/resistive Wall Mode (Rfmentioning

confidence: 99%

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

Gates¹,

Ahn²,

Allain³

et al. 2009

Nucl. Fusion

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The mission of the National Spherical Torus Experiment (NSTX) is the demonstration of the physics basis required to extrapolate to the next steps for the spherical torus (ST), such as a plasma facing component test facility (NHTX) or an ST based component test facility (ST-CTF), and to support ITER. Key issues for the ST are transport, and steady state high β operation. To better understand electron transport, a new high-k scattering diagnostic was used extensively to investigate electron gyro-scale fluctuations with varying electron temperature gradient scale length. Results from n = 3 braking studies are consistent with the flow shear dependence of ion transport. New results from electron Bernstein wave emission measurements from plasmas with lithium wall coating applied indicate transmission efficiencies near 70% in H-mode as a result of reduced collisionality. Improved coupling of high harmonic fast-waves has been achieved by reducing the edge density relative to the critical density for surface wave coupling. In order to achieve high bootstrap current fraction, future ST designs envision running at very high elongation. Plasmas have been maintained on NSTX at very low internal inductance l i ∼ 0.4 with strong shaping (κ ∼ 2.7, δ ∼ 0.8) with β N approaching the with-wall β-limit for several energy confinement times. By operating at lower collisionality in this regime, NSTX has achieved record non-inductive current drive fraction f NI ∼ 71%. Instabilities driven by super-Alfvénic ions will be an important issue for all burning plasmas, including ITER. Fast ions from NBI on NSTX are super-Alfvénic. Linear toroidal Alfvén eigenmode thresholds and appreciable fast ion loss during multi-mode bursts are measured and these results are compared with theory. The impact of n > 1 error fields on stability is an important result for ITER. Resistive wall mode/resonant field amplification feedback combined with n = 3 error field control was used on NSTX to maintain plasma rotation with β above the no-wall limit. Other highlights are results of lithium coating experiments, momentum confinement studies, scrape-off layer width scaling, demonstration of divertor heat load mitigation in strongly shaped plasmas and coupling of coaxial helicity injection plasmas to ohmic heating ramp-up. These results advance the ST towards next step fusion energy devices such as NHTX and ST-CTF.

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“…[10] in this paper, while ( Φ w / Φ x w ) − 1 is used in other articles [11][12][13][14]. The relation between S ↔ and (s E , α E ) can be expressed in terms of inductance coefficients and so-called the permeability of the plasma ↔ P .…”

Section: Exact Relation For Plasma Response and Implicationmentioning

confidence: 99%

Shielding of External Magnetic Perturbations By Torque In Rotating Tokamak Plasmas

Park¹,

Boozer²,

Ménard³

et al. 2009

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Investigation of resistive wall mode stabilization physics in high-beta plasmas using applied non-axisymmetric fields in NSTX*

Cited by 57 publications

References 30 publications

Shielding of external magnetic perturbations by torque in rotating tokamak plasmas

Shielding of external magnetic perturbations by torque in rotating tokamak plasmas

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

Shielding of External Magnetic Perturbations By Torque In Rotating Tokamak Plasmas

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