Nonlinear characteristics of RF-wave heated plasma in tokamaks

Summary form only given. In producing toroidal current in a tokamak by means of intense RF waves, the velocity distribution of electrons may be so far from Maxwellian. In this case, the Spitzer-Harm conductivity may not be a useful approximation and the electric field will play an important role. The characteristics of J/sub rf/(E) will be nonlinear when both RF power and DC electric field are present. In Fisch (1985), in the limit of E/spl rarr/0 this amount has been presented by a linear relation that introduces "induced" or "hot" conductivity. In the author\´s previous work the problem is solved without any limitation. In that reference for getting the conductivity, instead of solving the Fokker-Planck equation, an adjoint equation for the Green\´s function is solved. Therefore the corresponding influence function j(v) is the solution of the f/sub m/eE/m/spl part/j//spl part/ui+C*(j)=-f/sub m/qui where C* is the operator adjoint to the collision operator C. The current density J is calculated by J=/spl int/d/sup 3//spl nu/(S+(eE/m)f/sub m/e/spl I.oarr//sub /spl par//)/spl part/j//spl part//spl nu/. By solving such equations using a finite element code the characteristics of current density J versus E will be obtained. These characteristics of current density in region of -1<(v/sup 2/ q/m/spl Gamma/)E is similar to the characteristic of a p-n junction diode. Therefore it may play an important role. It is evident the solutions of equations give us the characteristic of fast electrons produced by RF heating that is located in plateau of distribution function. If we apply both RF power and AC electric field in regimes -1<(v/sup 2/q/m/spl Gamma/).E<1, the resulted RF plasma current will be rectified.