Fluid Moments in the Reduced Model for Plasmas with Large Flow Velocity

Abstract

Representation of particle fluid moments in terms of fluid moments in the modified guiding-centre model for flowing plasmas with large E × B velocity [N. Miyato et al., J. Phys. Soc. Jpn. 78, 104501 (2009)] is derived from the formal exact representation by a perturbative expansion in the subsonic flow case. It is similar to that in the standard gyrokinetic model in the long wavelength limit, except it has an additional flow term. The flow term has no effect on the representation for particle density, leading to the same representation as the standard one formally. In the conventional guiding-centre models for flowing plasmas, on the other hand, the representation for particle density is different from the standard one. This is due to the difference in the transformation for the guiding-centre position. Although the exact representation usually used in the standard gyrokinetic model has a different form from that in the modified guiding-centre case, correspondence between the two models is shown by considering the alternative form of exact representation in the standard gyrokinetic case. The representation for particle density is also obtained from the single particle Lagrangian by a variational method which is used to derive the representation in the transonic case.