MHD equilibrium and stability of a stellarator plasma

Коврижных, Л. М.; Shchepetov, S. V.

doi:10.1088/0029-5515/23/7/001

Cited by 32 publications

(24 citation statements)

References 9 publications

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“…The minimum value of DM also increases with increasing beta (Fig. 10), showing the beta selfstabilization effect [17], which is characteristic of the low-aspect-ratio torsatron configurations. The finite beta effects for the M = 6 configuration, corresponding to )3 0 = 11.7%, can be seen in Fig.…”

Section: Fragility Of the Magnetic Surfaces For Low-aspect-ratio Torsmentioning

confidence: 90%

Atomic Force Microscopy Observation of Stretched DNA on Graphite Surfaces

Yamamoto

Kanno

Tanaka

et al. 2003

Jpn. J. Appl. Phys.

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Section: Fragility Of the Magnetic Surfaces For Low-aspect-ratio Torsmentioning

confidence: 90%

Atomic Force Microscopy Observation of Stretched DNA on Graphite Surfaces

Yamamoto

Kanno

Tanaka

et al. 2003

Jpn. J. Appl. Phys.

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“…The increase in peak ␤ associated with the ECRH induces a larger Shafranov shift. This causes a stabilization effect 8,9 near the magnetic axis and finally even removes the qϭ2 surface from the plasma. The ideal mϭ2 becomes stable when q(0)Ͻ1.…”

Section: Introductionmentioning

confidence: 99%

Internal disruptions in Heliotron E*

et al. 1998

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In Heliotron E [K. Uo, Nucl. Fusion 25, 1243 (1985)] shifted-in vacuum magnetic field configuration, the q profile varies from just above 2 at the magnetic axis to 0.4 at the plasma edge. For low-β plasmas, resistive interchange modes are the dominant low-n instabilities at the plasma core. They saturate at low fluctuation levels. Above a threshold value, the ideal m/n=2/1 modes become unstable. They can be resonant or nonresonant modes depending on the value of q(0). In either case, their nonlinear evolution leads to a sudden crash of the pressure within the r/a=0.3 radius (sawtooth oscillation). When beta is increased further, the q=2 surface moves out of the plasma, and the ideal m/n=2/1 modes are effectively stabilized when q(0)<1.85. As a result, the sawtooth oscillations are suppressed.

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“…3; (B) rises proportionally with (p) for (p) < 0.3% and then decreases as (p) exceeds this value. During the thermal collapse phase, 9 Since there is no Ohmic current in ATF, we can quantify the fast-ion density n/ by measuring the beam-driven current for varying unidirectional injection power and find (experimentally) that rifOzP b /n}' 5 . For the high-/?…”

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confidence: 99%

Second stability in the ATF torsatron

Murakami

et al. 1989

Phys. Rev. Lett.

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Access to the MHD second stability regime has been achieved in the ATF torsatron. Experimental p values (j3 0 < 3%, with fast ions contributing « j of the pressure at high p) are well above the theoretical transition value (p c « 1.3% for ideal modes) required to reach this regime. The relatively low p c results from operation with peaked pressure profiles. The measured magnetic fluctuations decrease with increasing /?, and the pressure profile broadens. This behavior is consistent with theoretical predictions for p self-stabilization of resistive interchange modes. PACS numbers: 52.55.Hc, 52.30.Jb, 52.35.PyThe ideal magnetohydrodynamic (MHD) second stability regime has attracted increasing attention in toroidal confinement fusion research 1 ' 2 because it offers the hope of operation at high p=2fiop/B 2 (the ratio of the plasma kinetic pressure to the magnetic pressure) with favorable confinement, which would improve the prospects for a viable D-T fusion reactor. This theory predicts that the changes in the internal magnetic surfaces (plasma axis shift and shape) caused by an increase in plasma pressure act to stabilize instabilities driven by unfavorable field-line curvature. l As a result, the plasma can become more stable as p increases ("/? self-stabilization"), with an accompanying reduction in the anomalous transport induced by the curvature-driven instabilities. In this Letter we describe experiments in which operation in the second stability regime has been achieved at relatively low p in a torsatron (a type of stellarator).Because of their external control of magnetic configuration and the absence of plasma current, stellarators are well suited for exploring the second stability regime and studying p self-stabilization. In stellarators with significant shear (dx/dr > 0, where % is the rotational transform and r is the plasma minor radius) the dominant instabilities are interchange modes. 3,4 These modes can be stabilized by the magnetic well produced by the outward magnetic axis shift at finite p (Shafranov shift), and this p self-stabilization effect can open a stable path to the second stability regime. 5 ' 6 The ATF torsatron design was optimized to explore this possibili- ty. 7ATF is an / -2, twelve-field-period torsatron with major radius /?o™2.10 m, average minor radius a *=0.27 m, magnetic field on axis 5o<2T, central rotational transform £o«0.3, and edge transform ^f l «l. For the profile assumed in the ATF design studies 6 the p selfstabilization effect should dominate at /?o«5%. Electron-beam field mapping in early 1988 revealed substantial magnetic islands (6 cm wide at the x ™ T surface and smaller at other rational surfaces). 8 These islands, now corrected, acted as a magnetic limiter and effectively reduced the plasma radius to r p *=*0.6d (increasing the effective aspect ratio A from 8 to 10) and the effective edge transform Xa » 0.5. This led to a large increase in the Shafranov shift id/accp^A/xl) that enhanced the self-stabilization effect and afforded the results reported here, which ...

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MHD equilibrium and stability of a stellarator plasma

Cited by 32 publications

References 9 publications

Atomic Force Microscopy Observation of Stretched DNA on Graphite Surfaces

Atomic Force Microscopy Observation of Stretched DNA on Graphite Surfaces

Internal disruptions in Heliotron E*

Second stability in the ATF torsatron

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