Lower hybrid current drive in the presence of electric field

Abstract

Abstract.A new one-dimensional approach to the lower hybrid current drive (LHCD) modelling in the presence of an inductive electric field is suggested in this paper. The approach is based on using timedependent solutions of a well-known Fokker-Planck equation for the distribution function of fast electrons calculated concurrently with solving plasma transport equation in the Automated System for TRansport Analysis (ASTRA) [1]. A good agreement between experimental and modelling results is demonstrated for an FT-2 [2] plasma shot. Also new formulae for the steady-state solution of this kinetic equation are found. Analytical analysisThe well-known steady-state solution for the onedimensional distribution function of fast electrons in the absence of an electric field [3] is still used for the lower hybrid current drive modelling because of its simplicity combined with a rather good calculated driven current accuracy [4]. Actually, the electric field is only absent in a steady-state situation in which the plasma current is entirely driven by the waves. In most LHCD experiments the inductive electric field is present and can play a noticeable role in the LH current generation. In this paper we describe a steady-state solution of the 1D kinetic equation for the fast ( || ⁄ ≫ 1) electrons and discuss application of the solution to the lower hybrid (LH) current drive simulations. This equation has the following form in standard notations [5].Here ( It should be noted that the solution (2) in contrast to the solution (3) has a nonzero flux of fast electrons propagating in the direction of higher energies. In the particular case ( ) = 0, integrals in (2) can be calculated analytically. This simplifies solution (2) to a combination of the probability integral and elementary functions.Here the following notations are used: EPJ Web of Conferences 157, 03045 (2017)