  The plasma exit flow speed at the sheath entrance is constrained by the Bohm
criterion. The so-called Bohm speed regulates the plasma particle and power
exhaust fluxes to the wall, and it is commonly deployed as a boundary condition
to exclude the sheath region in quasi-neutral plasma modeling. Here the Bohm
criterion analysis is performed in the intermediate plasma regime away from the
previously known limiting cases of adiabatic laws and the asymptotic limit of
infinitesimal Debye length in a finite-size system, using the transport
equations of an anisotropic plasma. The resulting Bohm speed has explicit
dependence on local plasma heat flux, temperature isotropization, and thermal
force. Comparison with kinetic simulations demonstrates its accuracy over the
plasma-sheath transition region in which quasineutrality is weakly perturbed
and Bohm criterion applies.
