Study of High-Beta Magnetohydrodynamic Modes and Fast-Ion Losses in PDX.

McGuire, K.; Goldston, Robert James; Bell, Martin; Bitter, M.; Bol, K.; Brau, K.; Buchenauer, D.; Crowley, T. P.; Davis, S.; Dylla, F.; Eubank, H. P.; Fishman, Harvey M.; Fonck, R. J.; Grek, B.; Grimm, R.C.; Hawryluk, R. J.; Hsuan, H.; Hülse, R.; Izzo, R.; Kaita, R.; Kaye, S.; Kugel, H.; Johnson, D.; Manickam, J.; Manos, D. M.; Mansfield, D.K.; Mazzucato, E.; McCann, R.; McCune, D.; Monticello, D.; Motley, R. W.; Mueller, D.; Oasa, K.; Okabayashi, M.; Owens, Kevin G.; Park, W.; Reusch, M.F.; Sauthoff, N.; Schmidt, Géraldine; Šesnić, S.; Strachan, J.D.; Takahashi, H.; Tenney, F.; Thomas, P.; Towner, H. H.; White, R.B.; Surko, C. M.; Slusher, R. E.; Valley, J. F.

doi:10.1103/physrevlett.51.1925.2

Cited by 19 publications

(20 citation statements)

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“…This will be discussed more in the next section related to the EP loss. Another low frequency EP mode is the so-called fishbone instability which is an n ¼ 1 precessional drift resonant mode discovered in PDX, 311 and since then observed in virtually all NBI driven tokamaks. Fishbones are also seen in NSTX and MAST, but they have not been studied as a high priority since their physics is relatively well understood.…”

Section: B Energetic-particle-driven Modesmentioning

confidence: 99%

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: B Energetic-particle-driven Modesmentioning

confidence: 99%

Recent progress on spherical torus research

Ono

Kaita

2015

Physics of Plasmas

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“…1, using a paradigm of internal kink and classical fishbone. 18 For the low-frequency MHD mode with f f prec (f prec is the precession frequency of EPs), a finite EP population can provide MHD stabilization, 19,20 as was observed, for example, in the long sawtooth-free operation in JET. 21 On the other hand, with high power nearly perpendicular neutral beam injection experiments, large m=n ¼ 1=1 bursting "classical fishbone" mode can be excited, reducing the EP population.…”

Section: Introductionmentioning

confidence: 99%

“…21 On the other hand, with high power nearly perpendicular neutral beam injection experiments, large m=n ¼ 1=1 bursting "classical fishbone" mode can be excited, reducing the EP population. 18 (m is the poloidal mode number and n is the toroidal mode number. )…”

Section: Introductionmentioning

confidence: 99%

Off-axis fishbone-like instability and excitation of resistive wall modes in JT-60U and DIII-D

Okabayashi¹,

Matsunaga²,

deGrassie³

et al. 2011

Physics of Plasmas

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An energetic-particle (EP)-driven "off-axis-fishbone-like mode (OFM)" often triggers a resistive wall mode (RWM) in JT-60U and DIII-D devices, preventing long-duration high-b N discharges. In these experiments, the EPs are energetic ions (70-85 keV) injected by neutral beams to produce high-pressure plasmas. EP-driven bursting events reduce the EP density and the plasma rotation simultaneously. These changes are significant in high-b N low-rotation plasmas, where the RWM stability is predicted to be strongly influenced by the EP precession drift resonance and by the plasma rotation near the q ¼ 2 surface (kinetic effects). Analysis of these effects on stability with a self-consistent perturbation to the mode structure using the MARS-K code showed that the impact of EP losses and rotation drop is sufficient to destabilize the RWM in low-rotation plasmas, when the plasma rotation normalized by Alfvén frequency is only a few tenths of a percent near the q ¼ 2 surface. The OFM characteristics are very similar in JT-60U and DIII-D, including nonlinear mode evolution. The modes grow initially like a classical fishbone, and then the mode structure becomes strongly distorted. The dynamic response of the OFM to an applied n ¼ 1 external field indicates that the mode retains its external kink character. These comparative studies suggest that an energetic particle-driven "off-axis-fishbone-like mode" is a new EP-driven branch of the external kink mode in wall-stabilized plasmas, analogous to the relationship of the classical fishbone branch to the internal kink mode.

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“…Indeed, in NBIheated plasmas, trapped fast ions may transiently destabilize 1/1 modes. This so-called "fishbone" instability [55] is visible as a transient 1/1 mode on SXR channels. Its lifetime is typically a few milliseconds and it is characterized by a drop in 1/1 frequency due to the redistribution of fast ions (i.e.…”

Section: Displacement and Growth Ratementioning

confidence: 99%

Non-monotonic growth rates of sawtooth precursors evidenced with a new method on ASDEX Upgrade

et al. 2016

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Abstract. This paper describes a new method to derive, from Soft X-Ray (SXR) tomography, robust estimates of the core displacement, growth rate and frequency of a 1/1 sawtooth crash precursor. The method is valid for very peaked Soft X-Ray profiles and is robust against both the inversion algorithm and the presence of tungsten in a rotating plasma. Three typical ASDEX Upgrade crashes are then analysed. In all cases a postcursor is observed, suggesting incomplete reconnection. Despite different dynamics, in all three cases the growth rate of the core displacement shows similar features. First, it is not constant, supporting the idea of non-linear growth. Second, it can be divided into clearly identified phases with quasi-constant growth rates, suggesting sudden change of growth regime rather than smooth transitions. Third, its evolution is non-monotonic, with phases of accelerated growth followed by damped phases. This damping is interpreted for two cases respectively as an effect of fast ions and of mode coupling, based on the result of a MHD simulation. The mode frequency is observed in all cases to be closely related to the plasma bulk rotation profile, with little or no visible effect of the electron diamagnetic drift frequency. The onset criterion could not be clearly identified and it is shown that the role of the pressure gradient is not as expected from a naive extrapolation of the linear stability theory.

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Study of High-Beta Magnetohydrodynamic Modes and Fast-Ion Losses in PDX.

Cited by 19 publications

References 0 publications

Recent progress on spherical torus research

Recent progress on spherical torus research

Off-axis fishbone-like instability and excitation of resistive wall modes in JT-60U and DIII-D

Non-monotonic growth rates of sawtooth precursors evidenced with a new method on ASDEX Upgrade

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