The direct Ohmic heating of positive ions in tokamak plasmas

A universal Ohm's law is derived for the ion bootstrap current relative to the impurity ions. The contribution driven by q ir , the neoclassical plus electrostatic part of the ion heat flux, is found to be J iz = n i e ( i|| − z|| ) = 1.5 e 2 q ir B θ /m i T i (ν iz + 2ν ii ) and the frictional heating of the ions is J iz E ϕ [1−(1/Z eff )], which typically can be 10% to 15% of the total Ohmic heating when n z Z 2 ⩾n i .