Parasitic momentum flux in the tokamak core

A geometrical correction to the E×B drift causes an outward flux of co-current momentum whenever electrostatic potential energy is transferred to ion parallel flows. The robust, fully nonlinear symmetry breaking follows from the free-energy flow in phase space and does not depend on any assumed linear eigenmode structure. The resulting rotation peaking is counter-current and scales as temperature over plasma current. This peaking mechanism can only act when fluctuations are low-frequency enough to excite ion parallel flows, which may explain some recent experimental observations related to rotation reversals.