Pinches-Induced Transport Reduction in Reversed Shear/Optimized Shear Tokamak Plasmas

The analytical formulas for anomalous particle and ion thermal diffusivities, D^t_e and x^t_i, are derived on the basis of the two-fluid equations of our previous paper Chin. Phys. Lett. 15 (1998) 721. The two formulas involve five factors: (reversed/optimized) magnetic shear L_B( r ) , E x B sheared velocity V_E(r), where E is from the gradient of the ion pressure P_i, and the three ways of coupling between them, L^-1_B(dV_E/dr), L^-1_B V_E, and k .V_E , where k is the LB-dependent wavevector. It is found that the five factors can produce turbulent particle- and heat-pinch, i.e., D^t_e< 0 and x^t_i< 0, in the core region of tokamaks, and hence the effective particle and ion thermal diffusivities, D_e^eff and x_i^eff, reduce significantly in that region. The numerical results for D_e^eff and x_i^eff are in good agreement with experimental values.