Is the Weibel instability enhanced by the suprathermal populations or not?

Journal Article · Tue Jun 15 04:00:00 EDT 2010 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3446827· OSTI ID:21378021

Lazar, M ^[1]; Schlickeiser, R ^[2]; Poedts, S ^[3]

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1. Department of Research-Plasmas with Complex Interactions, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)
2. Department of Research-Plasmas with Complex Interactions, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Institut fuer Theoretische Physik IV, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)
3. Centre for Plasma Astrophysics, Celestijnenlaan 200B, 3001 Leuven (Belgium)

The kinetic instabilities of the Weibel type are presently invoked in a large variety of astrophysical scenarios because anisotropic plasma structures are ubiquitous in space. The Weibel instability is driven by a temperature anisotropy which is commonly modeled by a bi-axis distribution function, such as a bi-Maxwellian or a generalized bi-Kappa. Previous studies have been limited to a bi-Kappa distribution and found a suppression of this instability in the presence of suprathermal tails. In the present paper it is shown that the Weibel growth rate is rather more sensitive to the shape of the anisotropic distribution function. In order to illustrate the distinguishing properties of this instability a product-bi-Kappa distribution is introduced, with the advantage that this distribution function enables the use of different values of the spectral index in the two directions, kappa{sub ||}not =kappa{sub perpendicular}. The growth rates and the instability threshold are derived and contrasted with those for a simple bi-Kappa and a bi-Maxwellian. Thus, while the maximum growth rates reached at the saturation are found to be higher, and the threshold is drastically reduced making the anisotropic product bi-Kappa (with small Kappas) highly susceptible to the Weibel instability. This effect could also raise questions on the temperature or the temperature anisotropy that seems to be not an exclusive source of free energy for this instability, and definition of these notions for such Kappa distributions must probably be reconsidered.

• OSTI ID: 21378021
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 6 Vol. 17; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ANISOTROPY
DISTRIBUTION FUNCTIONS
ELECTRON TEMPERATURE
FUNCTIONS
INSTABILITY
INSTABILITY GROWTH RATES
ION TEMPERATURE
PLASMA INSTABILITY