Role of Impurity Cyclotron Damping in Ion Heating and RFP Turbulence

In the reversed field pinch ions are heated anomalously relative to collisional energy exchange with Ohmically heated electrons. The process channels electron energy to ions in a way that is still not understood. Recent observations suggest that impurities are preferentially heated. A theory for ion heating via impurity ioncyclotron-resonant damping of the turbulent energy cascaded from unstable global tearing modes is presented. The theory treats the magnetic turbulence as an Alfvén wave cascade and calculates the rate of damping to impurity ions via cyclotron resonances. The transient temperature rise in sawtooth crashes is modeled from a 0D transport model that accounts for the resonant cyclotron heating, anomalous heat losses, and collisional equipartition between impurities, bulk ions, electrons, and parallel and perpendicular temperatures. The larger fluctuation level at lower impurity cyclotron frequencies and the multiplicity of impurity resonances lead to heating rates that are consistent with experiment. Dependencies on temperature, density, and magnetic fluctuation level are described. The magnetic fluctuation spectrum is modeled for dissipation associated with viscosity, resistivity and cyclotron resonances. When Visco-resistive dissipation range spectra derived for MHD turbulence are fit to the MST spectrum, the viscosity and resistivity inferred are much larger than the experimental values. Analysis of asymmetry in the toroidal wavenumber spectrum suggests that additional dissipation is coming from the cyclotron resonance with impurity ions.