Effects of magnetic field curvature on Alfven wave heating of tokamak plasmas

AbstractMagnetic islands (MIs), resulting from a magnetic field reconnection, are ubiquitous structures in magnetized plasmas. In tokamak plasmas, recent researches suggested that the interaction between an MI and ambient turbulence can be important for the nonlinear MI evolution, but a lack of detailed experimental observations and analyses has prevented further understanding. Here, we provide comprehensive observations such as turbulence spreading into an MI and turbulence enhancement at the reconnection site, elucidating intricate effects of plasma turbulence on the nonlinear MI evolution.

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Parametric excitation of magnetoacoustic waves by a pump magnetic field in a high-β plasma

Journal of Plasma Physics ◽

10.1017/s0022377800020456 ◽

1977 ◽

Vol 17 (1) ◽

pp. 93-103 ◽

Cited By ~ 7

Author(s):

N. F. Cramer

Keyword(s):

Magnetic Field ◽

Parametric Excitation ◽

Acoustic Waves ◽

Magnetic Pressure ◽

Gas Pressure ◽

Alfven Wave ◽

Fast Wave ◽

Magnetoacoustic Waves ◽

Background Magnetic Field ◽

The Waves

The parametric excitation of slow, intermediate (Alfvén) and fast magneto-acoustic waves by a modulated spatially non-uniform magnetic field in a plasma with a finite ratio of gas pressure to magnetic pressure is considered. The waves are excited in pairs, either pairs of the same mode, or a pair of different modes. The growth rates of the instabilities are calculated and compared with the known result for the Alfvén wave in a zero gas pressure plasma. The only waves that are found not to be excited are the slow plus fast wave pair, and the intermediate plus slow or fast wave pair (unless the waves have a component of propagation direction perpendicular to both the background magnetic field and the direction of non-uniformity of the field).

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The role of slow magnetostrophic waves in dipole formation in rapidly rotating dynamos

10.5194/egusphere-egu21-15480 ◽

2021 ◽

Author(s):

Aditya Varma ◽

Binod Sreenivasan

Keyword(s):

Magnetic Field ◽

Threshold Value ◽

Dipole Field ◽

Wave Frequency ◽

Alfven Wave ◽

Inertial Waves ◽

Axial Dipole ◽

Wide Range ◽

The Magnetic Field

<p>It is known that the columnar structures in rapidly rotating convection are affected by the magnetic field in ways that enhance their helicity. This may explain the dominance of the axial dipole in rotating dynamos. Dynamo simulations starting from a small seed magnetic field have shown that the growth of the field is accompanied by the excitation of convection in the energy-containing length scales. Here, this process is studied by examining axial wave motions in the growth phase of the dynamo for a wide range of thermal forcing. In the early stages of evolution where the field is weak, fast inertial waves weakly modified by the magnetic field are abundantly present. As the field strength(measured by the ratio of the Alfven wave to the inertial wave frequency) exceeds a threshold value, slow magnetostrophic waves are spontaneously generated. The excitation of the slow waves coincides with the generation of helicity through columnar motion, and is followed by the formation of the axial dipole from a chaotic, multipolar state. In strongly driven convection, the slow wave frequency is attenuated, causing weakening of the axial dipole intensity. Kinematic dynamo simulations at the same parameters, where only fast inertial waves are present, fail to produce the axial dipole field. The dipole field in planetary dynamos may thus be supported by the helicity from slow magnetostrophic waves.</p>

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The development of magnetic field line wander by plasma turbulence

Journal of Plasma Physics ◽

10.1017/s0022377817000617 ◽

2017 ◽

Vol 83 (4) ◽

Cited By ~ 5

Author(s):

Gregory G. Howes ◽

Sofiane Bourouaine

Keyword(s):

Magnetic Field ◽

Field Line ◽

Magnetic Field Line ◽

Large Scale ◽

Magnetic Energy ◽

Plasma Turbulence ◽

Alfven Wave ◽

Astrophysical Plasmas ◽

Field Lines ◽

The Magnetic Field

Plasma turbulence occurs ubiquitously in space and astrophysical plasmas, mediating the nonlinear transfer of energy from large-scale electromagnetic fields and plasma flows to small scales at which the energy may be ultimately converted to plasma heat. But plasma turbulence also generically leads to a tangling of the magnetic field that threads through the plasma. The resulting wander of the magnetic field lines may significantly impact a number of important physical processes, including the propagation of cosmic rays and energetic particles, confinement in magnetic fusion devices and the fundamental processes of turbulence, magnetic reconnection and particle acceleration. The various potential impacts of magnetic field line wander are reviewed in detail, and a number of important theoretical considerations are identified that may influence the development and saturation of magnetic field line wander in astrophysical plasma turbulence. The results of nonlinear gyrokinetic simulations of kinetic Alfvén wave turbulence of sub-ion length scales are evaluated to understand the development and saturation of the turbulent magnetic energy spectrum and of the magnetic field line wander. It is found that turbulent space and astrophysical plasmas are generally expected to contain a stochastic magnetic field due to the tangling of the field by strong plasma turbulence. Future work will explore how the saturated magnetic field line wander varies as a function of the amplitude of the plasma turbulence and the ratio of the thermal to magnetic pressure, known as the plasma beta.

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A modular helical antenna for Alfvén wave heating in tokamaks

Nuclear Fusion ◽

10.1088/0029-5515/24/12/009 ◽

1984 ◽

Vol 24 (12) ◽

pp. 1679-1682 ◽

Cited By ~ 8

Author(s):

F. Hofmann ◽

K. Appert ◽

L. Villard

Keyword(s):

Alfven Wave ◽

Helical Antenna ◽

Wave Heating

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A two-dimensional analysis of the compressible flow near a reconnection site at the dayside magnetopause

Journal of Plasma Physics ◽

10.1017/s0022377806004338 ◽

2007 ◽

Vol 73 (1) ◽

pp. 89-115 ◽

Cited By ~ 3

Author(s):

LARS G. WESTERBERG ◽

HANS O. ÅKERSTEDT

Keyword(s):

Magnetic Field ◽

Transition Layer ◽

Alfven Wave ◽

The North ◽

Dayside Magnetopause ◽

Reconnection Site ◽

Ideal Magnetohydrodynamic ◽

North And South ◽

Magnetic Field Variations ◽

The Magnetic Field

Abstract.A compressible model of the magnetosheath plasma flow is considered. Magnetic reconnection is assumed to occur in a region stretching from the sub-Solar point to the north. Two locations of the reconnection site are treated: two and four Earth radii from the sub-Solar point, respectively. By treating the transition layer as very thin, we solve the governing equations approximately using the method of matched asymptotic expansions. The behavior of the magnetic field and the plasma velocity close to a reconnection site during the transition from the magnetosheath to the magnetosphere is investigated. We also obtain the development of the transition layer thickness north and south of the reconnection point. The magnetopause transition layer is represented by a large-amplitude Alfvén wave implying that the density is approximately the same across the magnetopause boundary. In order to match the solutions we consider a compressible ideal magnetohydrodynamic model describing density, velocity and magnetic field variations along the outer magnetopause boundary. We also compare the analytical results with solutions from a numerical simulation. The compressible effects on the structure of the magnetic field and the total velocity evolution are visible but not dramatic. It is shown that the transition layer north of the reconnection point is thinner than to the south. The effect is stronger for reconnection at higher latitudes.

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Compressional wave events in the dawn plasma sheet observed by Interball-1

Annales Geophysicae ◽

10.1007/s00585-999-1145-7 ◽

1999 ◽

Vol 17 (9) ◽

pp. 1145-1154 ◽

Cited By ~ 11

Author(s):

O. Verkhoglyadova ◽

A. Agapitov ◽

A. Andrushchenko ◽

V. Ivchenko ◽

S. Romanov ◽

...

Keyword(s):

Magnetic Field ◽

Time Series ◽

Field Line ◽

Plasma Sheet ◽

Inhomogeneous Plasma ◽

Partial Solution ◽

Alfven Wave ◽

Data Set ◽

Background Magnetic Field ◽

Phase Variations

Abstract. Compressional waves with periods greater than 2 min (about 10-30 min) at low geomagnetic latitudes, namely compressional Pc5 waves, are studied. The data set obtained with magnetometer MIF-M and plasma analyzer instrument CORALL on board the Interball-1 are analyzed. Measurements performed in October 1995 and October 1996 in the dawn plasma sheet at -30 RE ≤ XGSM and |ZGSM| ≤ 10 RE are considered. Anti-phase variations of magnetic field and ion plasma pressures are analyzed by searching for morphological similarities in the two time series. It is found that longitudinal and transverse magnetic field variations with respect to the background magnetic field are of the same order of magnitude. Plasma velocities are processed for each time period of the local dissimilarity in the pressure time series. Velocity disturbances occur mainly transversely to the local field line. The data reveal the rotation of the velocity vector. Because of the field line curvature, there is no fixed position of the rotational plane in the space. These vortices are localized in the regions of anti-phase variations of the magnetic field and plasma pressures, and the vortical flows are associated with the compressional Pc5 wave process. A theoretical model is proposed to explain the main features of the nonlinear wave processes. Our main goal is to study coupling of drift Alfven wave and magnetosonic wave in a warm inhomogeneous plasma. A vortex is the partial solution of the set of the equations when the compression is neglected. A compression effect gives rise to a nonlinear soliton-like solution.Key words. Magnetosphere physics (magnetotail) · Space plasma physics (kinetic and MHD theory; non-linear phenomena)

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