Coordinate-choice independent expression for drift orbit flux and flux-force relation in neoclassical toroidal viscosity theory

A coordinate-choice independent expression does not depend how the magnetic surface is parametrized by (\theta,\zeta). Flux-force relation in neoclassical toroidal viscosity(NTV) theory has been generalized in a coordinate-choice independent way. The expression for the surface averaged drift orbit flux in 1/\nu regime is derived without the requirement of straight field line coordinates. The resulted formula is insensitive to how the magnetic surface is parametrized and broadens the cases where flux-force relation can be applied. Construction of straight field line coordinates is avoided when the formula is used for numerical computation.