Guiding-center analysis of second-order RF interactions

The theory of second-order RF-plasma interactions is well developed and describes energy absorption and particle and momentum transport. While the second-order distribution function can be derived analytically, velocity moments are complex, and finite Larmour radius (FLR) or spectral-width approximations are used to make the necessary simplifications. The FLR approximation does not readily allow the analyses needed for high-harmonic ion Bernstein waves (IBW), while the spectral-width approximation cannot be readily understood in terms of physics approximations. A recent analysis suggested that velocity moments could be obtained without a direct evaluation of the distribution function. This approach is both simpler and more physics-based than the previous approach. However, the resulting moments differed from those obtained from the distribution function. Using guiding-center analysis, we have been able to carry out the program of moment evaluation sans distribution function based on an FLR expansion of the transformation back to laboratory coordinates. To zero order, there is no net particle or momentum transport. To first order, there is net momentum transport for short wavelength, FLR modes. This moment is the same as that obtained from the moment of the distribution function with a subsequent spectral-width approximation