Ohmic Flux Consumption During Initial Operation of the NSTX Spherical Torus

Ménard, J.; LeBlanc, B.; Sabbagh, S.A.; Bell, M.G.; Bell, R.E.; Fredrickson, E.; Gates, D.; Jardin, S.; Kaye, S.; Kugel, H.; Maingi, R.; Maqueda, R. J.; Mueller, D.; Ono, M.; Paul, S. F.; Skinner, C. H.; Stutman, D.

doi:10.2172/764943

Cited by 9 publications

(13 citation statements)

References 22 publications

(21 reference statements)

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“…The aspect-ratio scaling of MHD stability has been investigated based on modeling and experiment. 64,65 Thus far, while there are some observable trends as described in Secs. III and V, there have been no dramatic qualitative changes observed in the MHD stability and confinement properties with A for ST regimes.…”

Section: Aspect-ratio Scalingmentioning

confidence: 91%

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Recent progress on spherical torus research

Ono

Kaita

2015

Physics of Plasmas

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The spherical torus or spherical tokamak (ST) is a member of the tokamak family with its aspect ratio (A = R0/a) reduced to A ∼ 1.5, well below the normal tokamak operating range of A ≥ 2.5. As the aspect ratio is reduced, the ideal tokamak beta β (radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as β ∼ 1/A. The plasma current it can sustain for a given edge safety factor q-95 also increases rapidly. Because of the above, as well as the natural elongation κ, which makes its plasma shape appear spherical, the ST configuration can yield exceptionally high tokamak performance in a compact geometry. Due to its compactness and high performance, the ST configuration has various near term applications, including a compact fusion neutron source with low tritium consumption, in addition to its longer term goal of an attractive fusion energy power source. Since the start of the two mega-ampere class ST facilities in 2000, the National Spherical Torus Experiment in the United States and Mega Ampere Spherical Tokamak in UK, active ST research has been conducted worldwide. More than 16 ST research facilities operating during this period have achieved remarkable advances in all fusion science areas, involving fundamental fusion energy science as well as innovation. These results suggest exciting future prospects for ST research both near term and longer term. The present paper reviews the scientific progress made by the worldwide ST research community during this new mega-ampere-ST era.

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Section: Aspect-ratio Scalingmentioning

confidence: 91%

“…29, calculated ideal MHD stability limits for b T , j, and b N for fully self-sustained wall-stabilized equilibria as a function of aspect ratio are plotted. 64,65 The calculations show that b T increases rapidly as A decreases. The rapid b T increase is due to the combined effect of increasing j and b N as A is decreased by Eq.…”

mentioning

confidence: 95%

Recent progress on spherical torus research

Ono

Kaita

2015

Physics of Plasmas

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“…Figure 21b shows that the toroidal rotation is maintained at all radii measured -even near the plasma edge (R=1.4m). MSE-constrained reconstructions [41] and current profile analysis (not shown) indicate that the current profile reaches an equilibrium which is partiallyinductively-driven (30-40%) and with q min sustained near 1.2 (i.e. above 1 consistent with the avoidance of low-n MHD).…”

Section: Low-β Locked-mode Threshold Scalingsmentioning

confidence: 98%

“…In the later phases of these discharges (t > 1s), the plasma can also become unstable to fast rotating MHD instabilities (5-20kHz) including neoclassical tearing modes NTMs [40] or saturated kink [24] and interchange modes [41] which can also slow the plasma rotation, degrade confinement, and sometimes cause disruption. The DEFC system has insufficient bandwidth to respond to these instabilities, and these instabilities are best avoided through changes/increases in core safety factor and/or increases in shaping factor [42].…”

Section: Low-β Locked-mode Threshold Scalingsmentioning

confidence: 99%

Progress in understanding error-field physics in NSTX spherical torus plasmas

et al. 2010

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Abstract. The low aspect ratio, low magnetic field, and wide range of plasma beta of NSTX plasmas provide new insight into the origins and effects of magnetic field errors. An extensive array of magnetic sensors has been used to analyze error fields, to measure error field amplification, and to detect resistive wall modes in real time. The measured normalized error-field threshold for the onset of locked modes shows a linear scaling with plasma density, a weak to inverse dependence on toroidal field, and a positive scaling with magnetic shear. These results extrapolate to a favorable error field threshold for ITER. For these low-beta locked-mode plasmas, perturbed equilibrium calculations find that the plasma response must be included to explain the empirically determined optimal correction of NSTX error fields. In high-beta NSTX plasmas exceeding the n=1 no-wall stability limit where the RWM is stabilized by plasma rotation, active suppression of n=1 amplified error fields and the correction of recently discovered intrinsic n=3 error fields have led to sustained high rotation and record durations free of low-frequency core MHD activity. For sustained rotational stabilization of the n=1 RWM, both the rotation threshold and magnitude of the amplification are important. At fixed normalized dissipation, kinetic damping models predict rotation thresholds for RWM stabilization to scale nearly linearly with particle orbit frequency. Studies for NSTX find that orbit frequencies computed in general geometry can deviate significantly from those computed in the high aspect ratio and circular plasma cross-section limit, and these differences can strongly influence the predicted RWM stability. The measured and predicted RWM stability is found to be very sensitive to the E × B rotation profile near the plasma edge, and the measured critical rotation for the RWM is approximately a factor of two higher than predicted by the MARS-F code using the semi-kinetic damping model.

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“…This power can either increase the stored thermal energy of the plasma or be lost through transport or radiation. 80 The various terms in this expression are illustrated for a typical discharge in Fig. 8, for a discharge for 7.5 kV solenoid voltage ͑discharges with larger firing voltages tended to FIG.…”

Section: ͑19͒mentioning

confidence: 99%

Inductive Sustainment of Oblate FRCs with the Assistance of Magnetic Diffusion, Shaping and Finite-Lamor Radius Stabilization

Gerhardt¹,

Белова²,

Ji³

et al. 2008

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Oblate field-reversed configurations ͑FRCs͒ have been sustained for Ͼ300 s, or Ͼ15 magnetic diffusion times, through the use of an inductive solenoid. These argon FRCs can have their poloidal flux sustained or increased, depending on the timing and strength of the induction. An inward pinch is observed during sustainment, leading to a peaking of the pressure profile and maintenance of the FRC equilibrium. The good stability observed in argon ͑and krypton͒ does not transfer to lighter gases, which develop terminal co-interchange instabilities. The stability in argon and krypton is attributed to a combination of external field shaping, magnetic diffusion, and finite-Larmor radius effects.

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Ohmic Flux Consumption During Initial Operation of the NSTX Spherical Torus

Cited by 9 publications

References 22 publications

Recent progress on spherical torus research

Recent progress on spherical torus research

Progress in understanding error-field physics in NSTX spherical torus plasmas

Inductive Sustainment of Oblate FRCs with the Assistance of Magnetic Diffusion, Shaping and Finite-Lamor Radius Stabilization

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