Relaxation phenomena in reversed field pinches and tokamaks

A self-consistent theory is given for the field ε-vector ≡ generated by fluctuations (v-vector1 and B-vector1 are the velocity and magnetic fields, respectively) within the framework of resistive MHD, including the effects of plasma compressibility. Rigorous functional forms of ε-vector due to tearing and resistive interchange modes are given. It is shown that, in reversed field pinches, ε-vector produces relaxed states with reversed toroidal field in the vicinity of the 'Taylor state' J-vector = λ0B-vector, but with finite pressure gradients. In tokamaks, the theory is applied to calculate the turbulent resistivity governing current relaxation and to investigate MHD current drive ('F-θ pumping') and steady state operation using bootstrap currents. Numerical results on finite beta plasmas, based on reduced MHD equations, are presented. (author)