Magnetic reconnection and m = 1 oscillations in current carrying plasmas

Ara, G.; Basu, B.; Coppi, B.; Laval, G.; Rosenbluth, M. N.; Waddell, B. V.

doi:10.1016/s0003-4916(78)80007-4

Cited by 247 publications

(246 citation statements)

References 12 publications

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“…[15][16][17] When diamagnetic flows are included in the description of the internal kink, the growth rate of the resistive instability is further reduced and the mode can become completely stable. 8,13 It is also noted that the ideal MHD time scale required to recover the short crash times observed in the experiment appears to be at odds with the slow growth rate (in the resistive time scale) of the precursor oscillations that precede the crash. Several authors have proposed models that involve an acceleration of the reconnection rate during the late stage of the sawtooth ramp.…”

Section: Introductionmentioning

confidence: 90%

“…For example, in the resistivity dominated regime with diamagnetic flows, the linear growth rate of the internal kink at the marginal ideal stability point 8 can be expressed in the form cðc À ix Ãi Þðc þ ix Ãe Þ ' g. Thus, if S is to be varied while maintaining the characteristic timescale of this particular asymptotic regime constant, it is expected that the quantity S À1=3 =a should be kept constant. For instance, in the JET tokamak, using…”

Section: A Set Up Of Physical Parameters For the Simulationsmentioning

confidence: 99%

“…[6][7][8][9][10][11][12][13][14] It is noted that in ideal magnetohydrodynamics (MHD), with no dissipation mechanism available to enable magnetic reconnection, an unstable kink mode results in a three dimensional equilibrium with a m=n ¼ 1=1 helicity component (no kink cycles). In resistive MHD, kink cycles can be recovered, but the duration of kink crashes, s crash $ g À1=2 , is several orders of magnitude too slow with respect to the sawtooth crashes observed in large tokamaks.…”

Section: Introductionmentioning

confidence: 99%

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Diamagnetic thresholds for sawtooth cycling in tokamak plasmas

2011

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The cycling dynamics of the internal kink mode, which drives sawtooth oscillations in tokamak plasmas, is studied using the three dimensional, non-linear magnetohydrodynamic (MHD) code XTOR-2F [H. Lütjens and J.-F. Luciani, J. Comput. Phys. 229, 8130 (2010)]. It is found that sawtooth cycling, which is characterized by quiescent ramps and fast crashes in the experiment, can be recovered in two-fluid MHD provided that a criterion of diamagnetic stabilization is fulfilled. The simulation results indicate that diamagnetic effects alone may be sufficient to drive sawteeth with complete magnetic reconnection in high temperature Ohmic plasmas.

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Section: Introductionmentioning

confidence: 90%

Section: A Set Up Of Physical Parameters For the Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Diamagnetic thresholds for sawtooth cycling in tokamak plasmas

2011

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“…The theory of FLR stabilization of ideal MHD modes has been developed over many years. [8][9][10][11] For MHD modes, Roberts and Taylor 8 derived the FLR term from the stress tensor. Ara et al 9 investigated FLR effects on internal kink modes.…”

Section: Introductionmentioning

confidence: 99%

“…[8][9][10][11] For MHD modes, Roberts and Taylor 8 derived the FLR term from the stress tensor. Ara et al 9 investigated FLR effects on internal kink modes. Connor et al 10 showed that, in high-β plasmas, the calculation of FLR effects on the Mercier instability at high toroidal mode number n requires a solution of the ballooning equation.…”

Section: Introductionmentioning

confidence: 99%

Identification of Mercier instabilities in Alcator C-Mod tokamak

Ramos

Hastie

et al. 2000

Physics of Plasmas

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During current ramp-up discharges, highly localized magnetohydrodynamic (MHD) fluctuations were observed on the electron cyclotron emission (ECE) diagnostics of Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511]. The electron temperature profile was hollow, while the density profile was weakly decreasing. Assuming that the equilibration time was short enough to quickly thermalize ions the pressure profile was also found to be hollow. Using this pressure profile as an additional constraint to the EFIT program, an equilibrium with reversed shear was constructed having a q(0)1. The localized MHD activity was observed near the inner q=5 rational surface in this reconstructed equilibrium, where the Mercier criterion for ideal MHD stability was violated because of the reversed pressure gradient (dp/dr > 0), q > 1 and moderate shear. When kinetic effects were added, the ideal Mercier mode was finite ion Larmor radius (FLR) stabilized. However, ion Landau damping was found to be strong enough to drive a kinetic Mercier instability.

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“Ideal” tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

et al. 2016

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This paper discusses the transition to fast growth of the tearing instability in thin current sheets in the collisionless limit where electron inertia drives the reconnection process. It has been previously suggested that in resistive MHD there is a natural maximum aspect ratio (ratio of sheet length and breadth to thickness) which may be reached for current sheets with a macroscopic length L, the limit being provided by the fact that the tearing mode growth time becomes of the same order as the Alfvén time calculated on the macroscopic scale. For current sheets with a smaller aspect ratio than critical the normalized growth rate tends to zero with increasing Lundquist number S, while for current sheets with an aspect ratio greater than critical the growth rate diverges with S. Here we carry out a similar analysis but with electron inertia as the term violating magnetic flux conservation: previously found scalings of critical current sheet aspect ratios with the Lundquist number are generalized to include the dependence on the ratio de2/L2, where de is the electron skin depth, and it is shown that there are limiting scalings which, as in the resistive case, result in reconnecting modes growing on ideal time scales. Finite Larmor radius effects are then included, and the rescaling argument at the basis of “ideal” reconnection is proposed to explain secondary fast reconnection regimes naturally appearing in numerical simulations of current sheet evolution.

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Magnetic reconnection and m = 1 oscillations in current carrying plasmas

Cited by 247 publications

References 12 publications

Diamagnetic thresholds for sawtooth cycling in tokamak plasmas

Diamagnetic thresholds for sawtooth cycling in tokamak plasmas

Identification of Mercier instabilities in Alcator C-Mod tokamak

“Ideal” tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

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