Electron kappa distribution, quasi-thermal noise, and spontaneously-emitted electromagnetic fluctuations

Abstract:

Spacecraft measurements of charged particles in the solar wind near 1 A.U. show that their velocity distributions deviate from thermal Maxwellian model. Typically, the measured distributions feature energetic components with quasi scale-free power-law velocity dependence in the high velocity range. It is customary to model such a feature by means of the kappa distribution, but recently the kappa distribution is understood as implying that the space plasma is in non-extensive thermo-statistical state. Alternatively, the kappa distribution may imply that the space plasma is in turbulent quasi-equilibrium state. The non-extensive state and the turbulent-equilibrium may turn out to be nothing but two different ways of describing the same physical state, although the proof is not so straightforward. The solar wind near 1 A.U. also pervasively shows the presence of electrostatic fluctuations called the quasi-thermal noise. The present talk overviews the theory of solar wind electron kappa distribution, the associated quasi-thermal noise fluctuation, and the newly-discovered spontaneously-generated electromagnetic radiation, which can all be discussed within a single, unified framework of electromagnetic weak turbulence theory.