Localization of the magnetic reconnection zone during sawtooth crashes in tokamak plasmas

Munsat, T.; Park, H. K.; Classen, I. G. J.; Domier, Calvin; Donné, A. J. H.; Luhmann, Neville C.; Mazzucato, E.; Pol, M. J. van de

doi:10.1088/0029-5515/47/11/l01

Cited by 32 publications

(42 citation statements)

References 14 publications

(17 reference statements)

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“…This makes our observations relevant to the results of MST [19], where large spontaneous events include mode locking between modes with a range of different m and n numbers. Similar dynamics also appear to be important in recent observations of sawtooth reconnection [22] where higher order modes are observed before and after the reconnection events. In the closed cusp configuration, where the field lines are confined inside the experiment, the coupling between global modes and a current sheet leads to powerful bursts of 3D spontaneous reconnection [1].…”

Section: Discussionsupporting

confidence: 72%

“…On MST, Choi et al [19] found that small sawtooth events are linearly unstable and hence spontaneous, while larger events require a nonlinear mode coupling for the instability to grow. In sawtooth reconnection, detailed measurements by Park et al [9,20,21] and Munsat et al [22] from the TEXTOR tokamak found toroidally localization of the reconnection events, with reconnection starting at specific toroidal locations with both "good" and "bad" curvature. These observations show that the 2D theories may not capture the essential physics to describe the onset of spontaneous reconnection.…”

Section: Introductionmentioning

confidence: 98%

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Final Report: Laboratory Studies of Spontaneous Reconnection and Intermittent Plasma Objects

Egedal-Pedersen

Porkolab

2011

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Contributions Contributions within Discipline:As described above, we have identified spontaneous magnetic reconnection events in VTF. We find that the onset of reconnection is Three-dimensional, which is in contrast to the assumptions applied in most numerical simulation schemes. A Physical Review Letter was recently accepted for publication, detailing a new onset model for reconnection. Also we have derived new equations of state for guide-field reconnection. These equation has been extended to the case without a guide magnetic fields and control the structure of the inner reconnection region (see publications by A. Le et al. and J. Ng et al.) Contributions to Other Disciplines: Our recent finding on spontaneous reconnection is acquiring significant interest from scientists working on reconnection in the Earth magnetosphere and the Sun's corona.

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Section: Discussionsupporting

confidence: 72%

Section: Introductionmentioning

confidence: 98%

Final Report: Laboratory Studies of Spontaneous Reconnection and Intermittent Plasma Objects

Egedal-Pedersen

Porkolab

2011

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“…Given the results presented regarding 3D effects in magnetic reconnection, as well as the experiments by Park et al [64,65,66], which show that the sawtooth onset is toroidally and poloidally localized, it is clear that 2D theories of the sawtooth are insufficient. Specifically, the theories by Kadomtsev [17] and Wesson [117], which are often used to frame the sawtooth problem, require modification to reflect the new observations of toroidal localization.…”

Section: Applications To Tokamak Plasmasmentioning

confidence: 92%

“…These measurements, which take advantage of advances in electron cyclotron emission imaging [64,65,66], have shown that sawtooth onset is localized both toroidally and poloidally and that the temperature profile flattening is well-organized as opposed to stochastic [67]. The localization is observed even though the magnetic field geometry is mainly 2D.…”

Section: Reconnection In 3dmentioning

confidence: 99%

Experimental investigation of the trigger problem in magnetic reconnection

et al. 2011

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Magnetic reconnection is a fundamental process in plasma physics, which involves the often explosive release of magnetically stored energy in both space and laboratory plasmas. In order for this sudden release of energy to occur, there must be a period of slow reconnection, in which magnetic stress accumulates in the system, followed by a quick transition to fast reconnection. The question of what causes this transition is known as the 'trigger problem' and is not well understood.We address the trigger problem using the Versatile Toroidal Facility (VTF) at MIT, which we operate in the strong magnetic guide field regime. The resulting reconnection occurs in spontaneous events, in which there is a transition to fast reconnection. The reconnection in these events is asymmetric: it begins at one toroidal location and propagates toroidally in both directions. The spontaneous onset is facilitated by an interaction between the x-line current channel and a global mode, which breaks axisymmetry. We model the onset using an empirical Ohm's law and current continuity, which is maintained by ion polarization currents associated with the mode. The model reproduces the exponential growth of the reconnection electric field, and the model growth rate agrees well with the experimentally measured growth rate.We begin, however, by discussing reconnection in the collisional regime and the effect of neutral gas on plasma flows. We perform experiments which are relevant to plasmas at the edge of tokamaks, but may also be applicable to reconnection in the solar photosphere and the interstellar medium, where the ionization fraction is low. In these experiments, a plasma filament propagates across a magnetic field in a background of neutral atoms. The filament motion is driven by charge separation in an inhomogeneous magnetic field, and this drive is balanced by collisional damping. The filament propagation and internal structure are described in detail.

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“…in the direction co-or counter-aligned with the reconnection electric field. Observational signatures of the RR localization (Munsat et al, 2007) and motion in solar flares (Qiu, 2009) and laboratory experiments (Katz et al, 2011) indicate that the reconnection magnetic structure can propagate at a substantial fraction of the local Alvén speed with respect to surrounding plasma, but there have been few numerical studies that have focused on the propagating RR phenomenon (e.g. Lapenta et al, 2006 and references therein).…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional magnetic reconnection through a moving magnetic null

Lukin

Linton

2011

Nonlin. Processes Geophys.

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Abstract.A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.

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Localization of the magnetic reconnection zone during sawtooth crashes in tokamak plasmas

Cited by 32 publications

References 14 publications

Final Report: Laboratory Studies of Spontaneous Reconnection and Intermittent Plasma Objects

Final Report: Laboratory Studies of Spontaneous Reconnection and Intermittent Plasma Objects

Experimental investigation of the trigger problem in magnetic reconnection

Three-dimensional magnetic reconnection through a moving magnetic null

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