Effects of orbit squeezing on transport fluxes

When the ratio μ_lⁱ/μ_lⁱ is of the order of unity, electron transport fluxes such as bootstrap current can be affected by the ion orbit squeezing. Here,μ_lⁱ is the electron viscous coefficient, andμ_lⁱ is the ion viscous coefficient with the effects of ion orbit squeezing included. The condition μ_lⁱ/μl_l^e≃1 can be satisfied for plasmas, such as those in enhanced reversed shear (ERS) mode, with ion temperature greater than electron temperature and orbit squeezing factor S≫ 1. Transport fluxes for both standard squeezed banana orbits and for squeezed orbits close to the magnetic axis are calculated for a large aspect ratio tokamak. It is found that ion heat flux and bootstrap current are reduced in ERS-like plasmas. Furthermore, the bootstrap current density does not vanish on the magnetic axis for a parabolic pressure profile in minor radius r due to the finite value of the fraction of trapped particles. This makes it possible to operate tokamaks in steady state.