An estimate of the ion orbit loss rate in tokamaks

The ion orbit loss rate in the edge region of a tokamak is estimated from an orbit-averaged Coulomb collision operator. The mechanism of the ion orbit loss in a tokamak is qualitatively different from that of the electron loss in a mirror machine, because ion orbit loss in a tokamak results from the coupling between the configuration-space diffusion and the velocity-space scattering, while the electron loss in a mirror machine results from the velocity-space scattering. Despite this difference, the magnitudes of the ion orbit loss rate in a tokamak estimated from these two concepts are similar. Because the ion orbit loss flux is related to the plasma viscosity, it represents a loss of poloidal momentum.