Gyroviscous stability theory with application to the internal tilt mode of a field-reversed configuration

The variational formulation for a gyroviscous fluid plasma is constructed. This theory offers a fluid-based description of perpendicular kinetic effects, generally called finite Larmor radius (FLR) effects. This approach avoids the complexity of a more complete kinetic treatment and avoids local singularities that can appear in the standard FLR expansion treatment. The method is applied to the internal tilt mode of a field-reversed configuration (FRC), an instance where standard FLR theory clearly breaks down. The relative simplicity of the variational gyroviscous fluid theory allows easy computation of stability properties, including the scaling of marginal stability conditions.