The theory of the early nonlinear stage of <i>m</i>=1 reconnection in tokamaks*

Zakharov, L.; Rogers, B. N.; Migliuolo, S.

doi:10.1063/1.860735

Cited by 84 publications

(83 citation statements)

References 23 publications

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“…Unfortunately, even for high beta plasmas, the growth rate is still too slow to be compared with the time scale of fast events such as solar flares and magnetospheric substorm onsets, due to the fact of the ion plasma frequency, attracted more attentions in 1990s [12][13][14][15]. A fast growth rate in the sub-Alfvénic regime for nonlinear kink-tearing modes in tokamak plasmas was found scaled as [14,15].…”

Section: / 4πmentioning

confidence: 99%

Recent progresses in theoretical studies and satellite observations for collisionless magnetic reconnection

Wang

Xiao

et al. 2012

Chin. Sci. Bull.

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As an essential mechanism in large scale fast magnetic energy releases and field reconfigurations processes in space, astrophysical, and laboratory plasmas, magnetic reconnection, particularly collisionless magnetic reconnection, has been studied for more than 65 years. Many progresses have been achieved in recent years and basic features of the process have been well understood, largely due to more and more satellite observation data available in the last decade. However, a few outstanding issues are still remained unresolved. We in the paper review the development of collisionless magnetic reconnection studies and major achievements in recent years, and also briefly discuss the open questions remained to be answered in studies of collisionless magnetic reconnection. Magnetic reconnection is thought an essential mechanism in many plasma physics processes in space, laboratory, and astrophysical objects, related to configurations relaxation and fast release of magnetic field and energy, observed in laboratory experiments and satellites observations and studied in numerical simulations and theoretical analysis [1]. The concept of magnetic reconnection was first proposed as a process of oppositely directed magnetic field lines merging and annihilated at a magnetic null, in an effort to understand the solar flare phenomenon It has then become a fundamental model in magnetic reconnection studies. Nevertheless, the Sweet-Parker reconnection rate is on the order of square root of the electrical resistivity. Due to the low collisionality in space and solar plasmas, the rate is too slow to be counted for fast events such as solar flares.Another model was then proposed by Petschek, with a fast driven and an X-point geometry, to solve the problem [5]. It was claimed in the Petschek model that a fast reconnection rate could be almost on the order of logarithm of resistivity, much faster than the Sweet-Parker rate. It was however found latterly that in high resolution simulations, the X-point geometry could not be realized in high Lundquist number regime of S≥10 4 [6]. And in the low Lundquist number regime (S<10 3 ), Petschek reconnection rate and Sweet-Parker reconnection rate would be more or less on the same order. On the other hand, collisionless mechanisms such as the finite Larmor radius (FLR) effect rather than collisional

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Section: / 4πmentioning

confidence: 99%

Recent progresses in theoretical studies and satellite observations for collisionless magnetic reconnection

Wang

Xiao

et al. 2012

Chin. Sci. Bull.

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“…The reconnection dynamics can be either mostly resistive (see [9]) or collisionless (see [10]). Since we assume that we operate in conditions of a DT experiment in JET, we may use the collisionless estimate for the complete reconnection time: The crash times that we consider in this study are τ cr ∼ 144µs in section 4 and τ cr ∼ 90µs in section 5.…”

Section: Dynamics Of the Sawtooth Collapsementioning

confidence: 99%

Redistribution of fast ions during sawtooth reconnection

2014

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In a tokamak-based fusion power plant, possible scenarios may include regulated sawtooth oscillations to remove thermalized helium from the core of the plasma. During a sawtooth crash, the helium ash and other impurities trapped in the core are driven by the instability to an outer region. However, in a fusion plasma, high energy ions will represent a significant population. We thus study the behaviour of these energetic particles during a sawtooth. This paper presents the modelling of the redistribution of fast ions during a sawtooth reconnection event in a tokamak plasma. Along the lines of the model for the evolution of the flux surfaces during a sawtooth collapse described in Ya.I. Kolesnichenko and Yu.V. Yakovenko 1996 Nucl. Fusion 36 159, we have built a time-dependent electromagnetic model of a sawtooth reconnection. The trajectories of the ions are described by a complete gyro-orbit integration. The fast particles were evolved from specific initial parameters (given energy and uniform spread in pitch) or distributed initially according to a slowing-down distribution created by fusion reactions. Our modelling is used to understand the main equilibrium parameters driving the motions during the collapse and to determine the evolution of the distribution function of energetic ions when different geometries of reconnection are considered.

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“…[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%

“…Several authors have proposed models that involve an acceleration of the reconnection rate during the late stage of the sawtooth ramp. 12,[18][19][20][21][22] In a preceding work, 23 the internal kink dynamics were studied, revealing a threshold between cases displaying a saturated m=n ¼ 1=1 helical state in the plasma core, and regimes where the kink is oscillating in time. The transition between these dynamics is controlled by plasma pressure, resistivity, thermal transport, and diamagnetic effects.…”

Section: Introductionmentioning

confidence: 99%

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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The theory of the early nonlinear stage of m=1 reconnection in tokamaks*

Cited by 84 publications

References 23 publications

Recent progresses in theoretical studies and satellite observations for collisionless magnetic reconnection

Recent progresses in theoretical studies and satellite observations for collisionless magnetic reconnection

Redistribution of fast ions during sawtooth reconnection

Diamagnetic thresholds for sawtooth cycling in tokamak plasmas

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