Physical Mechanisms of the Electron Energy Distribution Function Control in Inhomogeneous Non-stationary Plasma*

To predict the main scenarios of electron distribution function (EDF) control, first of all it is necessary to develop a kind of roadmap of formation a different modes of the EDF in the inhomogeneous unsteady plasma. The analysis shows that the time scales are determined by the ratio between the transient time tL (the characteristic time of electron transport through the plasma volume) and the relaxation times te of the EDF momentum tm (on velocity direction) and energy. Accordingly, for the spatial variable it is the ratio between the characteristic size of plasma L and an electron mean free path l (momentum relaxation) and a length of energy relaxation of electron energy le. A significant difference between the scale of momentum relaxation and energy te $>>$ tm, le $>>$ l (reaching two or more orders of magnitude), allows to predict the possible modes of the EDF formation, with various degrees of selectivity effects on different groups of electrons (from a local EDF when L $>>$ le and it is possible to affect only the entire ensemble of electrons) and the nonlocal EDF, when L $<<$ le and different groups of electrons behave independently of each other and it is possible to influence only on the interest profiles.