Plasma decontamination and energy transport by impurity driven modes

A radial flow of impurities toward the outer edge of a magnetically confined plasma is produced, following an accumulation of impurities at the center of the plasma column, by impurity density gradient driven modes for realistic values of the temperature gradient of the main ion population relative to its density gradient. At the same time an outward transport of the main ion thermal energy is also induced. For mean free paths of the main ion population shorter than the relevant longitudinal wavelengths, these modes can be described by moment equations and are associated with the finite thermal conductivity of the main ions. In the opposite (collisionless) limit, mode-particle resonances replace the effects of finite ion thermal conductivity and in addition, modes that are standing along the magnetic field lines are affected by the magnetic trapping of a fraction of the main ion population. The expression for their growth rate is strongly influenced by the ratio of the effective trapped ion collision frequency to the mode frequency and under realistic conditions, can be independent of mode− particle resonance processes that involve only a relatively small portion of velocity space.