RELAX - a computer code for the study of collisional and wave driven relaxation of the electron distribution function in toroidal geometry

Abstract

The Fokker-Planck quasilinear code RELAX is described. The code solves the bounce-averaged Fokker-Planck equation for the evolution of the electron momentum distribution on a number of magnetic surfaces in a tokamak. The physics models incorporated in the code include bounce-averaged, approximate collision operators, electric field driven momentum space convection, and quasilinear diffusion due to electron cyclotron resonant heating. Interfaces are provided with the HELENA toroidal MHD equilibrium code (G.T.A. Huysmans et al., proceedings of the CP90 Europhysics Conference on Computational Physics, 10-13 September 1990, Amsterdam, The Netherlands, Editor A. Tenner, World Scientific, Singapore, (1991) p. 371) and with the TORAY ray-tracing code (A.H. Kritz et al., proceedings of the 3{sup rd} Intern. Symposium on Heating in Toroidal Plasmas, Grenoble (France), 22-26 March (1982) Vol. II, p. 707). A number of test cases are presented in which the code results are compared with known analytical results. The code will be used for the study of the generation and the behaviour of nonthermal electron populations in tokamak experiments. Another application of the code will be the study of non-inductive current drive by electron cyclotron waves. (orig.)