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Question on energy conversion in MHD

  1. Sep 6, 2010 #1
    During the astrophyscial MHD class, I got a simple question on conversion of magnetic energy to plasma's kinetic energy and vice versa.

    When macroscopic magnetic force is exerted on a chunk of conducting fluid, we say work is done by B-field and magnetic potential energy is converted into fluid's kinetic energy.

    But in a microscopic point of view, there seems to be no physical agent that does work on charged particles because we ignore electric field in the pure MHD limit.

    The Lorentz force on each charged particle due to B-field just deflects particle's motion perpendicular to its direction of motion and hence does no work.

    How can I reconcile both concepts?

    My guess is that the electric field hidden behind the MHD equation plays a role in doing work on charged particles.

    And I think it is somehow related to the fact that the macroscopic electric current density vector j_e is not in general equal to the bulk motion of the fluid v.

    Could you give me a better explanation on this problem with a simple example?
    Thank you...
  2. jcsd
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