Decay of poloidal rotation in a tokamak plasma

Radial electric fields may be built up in a tokamak by several mechanisms such as nonambipolar particle transport or loss, or the inhomogeneous deposition of electric charge which occurs as a result of the injection of fast neutral atoms. The initial effect of the radial fields is to produce a poloidal rotation of the plasma. Such rotation, however, subjects the moving elements of the plasma to energy dissipation by magnetic pumping, which damps the rotation in a period of the order of the ion-ion collision time. The problem is analyzed for the “plateau” and “banana” regimes by applying the drift kinetic equation, with a simple relaxation collision term, to a slab-model low-β plasma. The calculation may be more generally applied to the problem of momentum dissipation for any low-β long-mean-free-path plasma in a periodic or stochastic magnetic field.