Current drive from RF-induced modulation of plasma magnetization

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Abstract
Spatial modulation of the average magnetic moment 〈μ〉 of the electrons or ions in a tokamak can be used to impose a net toroidal force on that species due to the interaction of each particle’s magnetic moment with the magnetic variations which the particle experiences as it moves along a flux tube. Both sign and magnitude of the net toroidal force depend on the spatial relationship between the variation of average magnetic moment and the variation of magnetic field strength. The average parallel energy change is calculated as a function of the variation of average magnetic moment, the variation in B along the flux tube, and the phase between the variations of 〈μ〉 and of B. Spatial modulation of the average magnetic moment can result from asymmetric cyclotron heating of a species, provided that distribution function relaxation mechanisms are strong enough to maintain steady‐state. We have developed an experimental method of directly investigating the changes in distribution function which result from the application of RF power to a plasma, and results of these measurements will be presented, as will computational simulations which pertain to the use of the above as a steady‐state current drive mechanism.

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