Modelling of Electrostatic Solitary Waves and Shocks in Non-Maxwellian Plasmas: A Review of Recent Results

Thursday, 18 December 2014
Ioannis Kourakis1, Gina Williams1, Sharmin Sultana2 and Manfred Hellberg3, (1)Centre for Plasma Physics, Belfast, United Kingdom, (2)Jahangirnagar University, Dhaka, Bangladesh, (3)University of Kwazulu Natal, School of Physics, Durban, South Africa
Space plasmas are often characterized by the presence of energetic particles in the background, e.g. due to various electron acceleration mechanisms [1]. This phenomenon is associated with a power-law dependence at high (superthermal) velocity values, modeled by a kappa-type distribution function, which reproduces observed data more efficiently that the standard Maxwellian distribution approach [2]. It has been shown from first principles that this ubiquitous superthermal feature of plasmas may alter the propagation characteristics of plasma modes, and modify the plasma screening properties [3].

In this presentation I will review, from first principles, the effects of a non-Maxwellian electron distribution on the characteristics of electrostatic plasma modes. A kappa distribution function [1] is employed to model the deviation of a plasma constituent (electrons, in general) from Maxwellian equlibrium. It will be shown that the excess in superthermal propulation modifies the charge screening mechanism, affecting the dispersion laws of both low- and higher frequency modes significantly. Various experimental observations may thus be interpreted as manifestations of excess superthermality [2]. Focusing on the features of nonlinear excitations (shocks, solitons), we investigate the role of superthermality in their propagation dynamics (existence laws, stability profile) and dynamical profile [3]. The relation to other nonthermal plasma theories is briefly discussed.

[1] See V.M. Vasyliunas, J. Geophys. Res. 73, 2839 (1968), for a historical reference; also, V. Pierrard and M. Lazar, Solar Phys. 267, 153 (2010), for a more recent review.
[2] M. Hellberg et al, J. Plasma Physics 64, 433 (2000); G. Sarri et al, Physics of Plasmas, 17, 010701/1-4 (2010).
[3] S. Sultana, I. Kourakis, N.S. Saini, M.A. Hellberg, Phys. Plasmas 17, 032310 (2010);
S. Sultana and I. Kourakis, Plasma Phys. Cont. Fus. 53, 045003 (2011);
S. Sultana, G. Sarri and I. Kourakis, Phys. Plasmas 19, 012310 (2012);
I. Kourakis, S. Sultana and M.A. Hellberg, Plasma Phys. Cont. Fusion, 54, 124001 (2012);
G. Williams and I. Kourakis, Plasma Physics and Controlled Fusion 55, 055005/1-13 (2013); G. Williams, F. Verheest, M. Hellberg and I. Kourakis, Phys. Rev. E (submitted, 2014).