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

The analytical formulas for anomalous particle and ion thermal diffusivities,Dte and xti,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 LB(r),E x B sheared velocity VE(r),where E is from the gradient of the ion pressure Pi,and the three ways of coupling between them,L-1B(dVE/dr),L-1B VE,and k.VE,where k is the LB-dependent wavevector.It is found that the five factors can produce turbulent particle-and heat-pinch,i.e.,Dte<0 and xti<0,in the core region of tokamaks,and hence the effective particle and ion thermal diffusivities,Deeff and xieff,reduce significantly in that region.The numerical results for Deeff and xieff are in good agreement with experimental values.