Could you give an intuition about why does MHD requires the following condition in time and spatial scales, please? Thanks.

At scales much larger than the mean free path and gyroradius, and time scales much larger than the collision time and gyroperiod, the magnetohydrodynamics (MHD) model is good.

  • $\begingroup$ If you take out the gyroradius & gyroperiod, would you agree that the statement holds for a fluid description? $\endgroup$
    – Kyle Kanos
    Commented Sep 30, 2023 at 19:00
  • 1
    $\begingroup$ If you allow for gyro motion of different species of particles, the best approximation you can get away with is a multi-fluid plasma (strictly speaking, MHD is usually treated as a single fluid when people say "MHD plasma"... otherwise they will specify it is a multi-species magnetized fluid). $\endgroup$ Commented Dec 18, 2023 at 21:57


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.