ABSTRACT

It is often remarked that Equations (7.1)–(7.4) are identical to the equations governing the motion of an inviscid, adiabatic, perfectly conducting, electrically neutral, liquid. Indeed, this observation is sometimes used as the sole justification for adopting the MHD equations. After all, a hot, tenuous, quasi-neutral plasma is highly conducting, and if the motion is sufficiently rapid then viscosity and heat conduction can both plausibly be neglected (which implies that the motion is adiabatic). However, as should be clear from the discussion in Section 4.11, this is a highly oversimplified and misleading argument. The problem, of course, is that a weakly coupled plasma is a far more complicated dynamical system than a conducting liquid.