Anisotropic ion heating in the MST RFP*

In the Madison Symmetric Torus reversed-field pinch, discrete bursts of magnetic reconnection liberate a large amount of energy ($\sim $20 kJ) from the equilibrium magnetic field, a significant fraction of which (10-25{\%}) becomes ion thermal energy, more than doubling T$_{i}$ in $<$ 100 $\mu $sec. Recent charge exchange recombination spectroscopy measurements of the C$^{+6}$ impurity ion temperature reveal that this heating is often anisotropic, such that the rise in perpendicular temperature is greater than or equal to the rise in parallel temperature. Furthermore, the magnitude of the rise in both temperatures is lessened as the plasma density increases, although this effect is more pronounced for the parallel temperature. Models of ion heating are reviewed in light of these observations.