The developments in satellite technology revealed that particle distributions in space plasmas are more often suprathermal (kappa distribution) than thermal (Maxwellian distribution). In the case of several instabilities, theoretical calculations and numerical experiments have shown that instability thresholds and rates of energy transfer between fields and particles are modified in the presence of a kappa distribution with respect to Maxwellian distribution. In the case of plasmoid instability, this could have profound implications in terms of energy transfer to particles. Several observational studies have tried to measure the amount of energy transferred to particles, ions and electrons, in reconnection events in different environments. In light of such observations, a theoretical model is necessary to explain such observations. In this first part of my talk, I will discuss about the development of theoretical modelling of plasmoid instability.
In the second part of my talk, I will be discussing about a ubiquitous structure observed in space and astrophysical plasmas called coherent bipolar electric field structures. Theoretical analysis of such these structures can be addressed using BGK approach. Bernstein, Greene, and Kruskal (BGK) have developed the theory for one-dimensional stationary nonlinear electrostatic waves in a collisionless plasma. It is a nonlinear kinetic theory formulated in the Vlasov-Poisson framework of equations. If the solution obtained after the BGK analysis is positive, the solution represents a coherent electrostatic structure, usually called a BGK wave. These structures are also called phase space holes that develop because of particle trapping in a potential, a phase space manifestation of BGK wave. These structures in phase space have a lower density at the center than the rim; they are "Phase Space Holes." Depending on which species are trapped, phase space holes are further classified as Electron Holes (EHs) and Ion Holes (IHs). From a kinetic point of view, the coherent electrostatic structures encountered in space plasmas are modeled in terms of these different phase space holes. The characteristics of these coherent electric field structures in superthermal plasmas will be discussed in this talk.
Speaker: Dr. Harikrishnan Aravindakshan