Magnetohydrodynamic Equations for Finite Larmor Radius

Calculations using two-fluid magnetohydrodynamic equations (B. Lehnert, Phys. Rev. Letters 7: 442(1961)) appear to show cancellation of a stabilizing effect (M. N. Rosenbluth, et. al., Conference on Plasma Physics and Controlled Nuclear Fusion Research, Salzburg (1961)). It is shown that the cancellation resulted from using only the scalar pressure in the ion equation of motion. Derivations of additional factors using modifications to both the ion pressure tensor and Ohm's law are presented. (L.N.N.)