Viscosity in a magnetized plasma: Physical interpretation

We provide a physically motivated alternate derivation of the η 0 terms in the viscous stress tensor given by Braginskii (1965) and others. We show that the η 0 terms are fully accounted for by a gyrotropic diagonal pressure tensor; off‐diagonal terms do not contribute to the η 0 part of the viscous stress. The η 0 part of the viscous stress results from the plasma's tendency to develop small thermal anisotropies as it evolves. Collisions oppose the production of anisotropy and ultimately lead to irreversible heating.