Phase slips and dissipation of Alfvenic intermediate shocks and solitons

Journal Article · Sat Sep 15 04:00:00 EDT 2012 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4754280· OSTI ID:22086121

Laveder, D; Passot, T; Sulem, P L ^[1]

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1. Universite de Nice-Sophia Antipolis, CNRS, Observatoire de la Cote d'Azur, B.P. 4229, 06304 Nice Cedex 4 (France)

The time evolution of a rotational discontinuity, characterized by a change of the magnetic-field direction by an angle {Delta}{theta} such that {pi}<|{Delta}{theta}|<2{pi} and no amplitude variation, is considered in the framework of asymptotic models that, through reductive perturbative expansions, isolate the dynamics of parallel or quasi-parallel Alfven waves. In the presence of viscous and Ohmic dissipation, and for a zero or sufficiently weak dispersion (originating from the Hall effect), an intermediate shock rapidly forms, steepens and undergoes reconnection through a quasi gradient collapse, leading to a reduction of |{Delta}{theta}| by an amount of 2{pi}, which can be viewed as the breaking of a topological constraint. Afterwards, as |{Delta}{theta}|<{pi}, the intermediate shock broadens and slowly dissipates. In the case of a phase jump |{Delta}{theta}|>3{pi}, which corresponds to a wave train limited on both sides by uniform fields, a sequence of such reconnection processes takes place. Differently, in the presence of a strong enough dispersion, the rotational discontinuity evolves, depending on the sign of {Delta}{theta}, to a dark or bright soliton displaying a 2{pi} phase variation. The latter is then eliminated, directly by reconnection in the case of a dark soliton, or through a more complex process involving a quasi amplitude collapse in that of a bright soliton. Afterwards, the resulting structure is progressively damped. For a prescribed initial rotational discontinuity, both quasi gradient and amplitude collapses lead to a sizeable energy decay that in the collisional regime is independent of the diffusion coefficient {eta} but requires a time scaling like 1/{eta}. In the non-collisional regime where dissipation originates from Landau resonance, the amount of dissipated energy during the event is independent of the plasma {beta}, but the process becomes slower for smaller {beta}.

• OSTI ID: 22086121
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 9 Vol. 19; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALFVEN WAVES
AMPLITUDES
ASYMPTOTIC SOLUTIONS
BETA RATIO
DIFFUSION
DISPERSIONS
HALL EFFECT
LANDAU FLUCTUATIONS
MAGNETIC FIELDS
MAGNETIC RECONNECTION
PLASMA EXPANSION
SHOCK WAVES
SOLITONS
TOPOLOGY