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Plasma in a Magnetic Field

  1. Feb 8, 2012 #1
    I was wondering, if plasma moves moves in the same direction as a magnetic field when placed in a magnetic field, it seems that plasma would be in a perpetual state of motion if suspended inside a torus created by ring magnets, such as a tokamak. Wouldn't this violate the laws of thermodynamics, because you would essentially be creating perpetual motion? Or am I missing something?
  2. jcsd
  3. Feb 8, 2012 #2


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    Staff: Mentor

    The magnets don't cause the plasma to move. The particles themselves are in motion due to thermal motion (heat). The magnetic fields merely confine and guide the plasma. If the plasma cools down too far the ions will combine with the electrons and the plasma will cease to be a plasma and turn back into a normal gas.

    Particles will spiral around the magnetic field lines and will be repelled by a gradiant in the field, but other than that they magnets don't do much else.
  4. Sep 20, 2012 #3
    You're talking about a ferromagnetic fluid yes? It'd have to be a particle suspension that could respond to an array of different charges to follow the magnetic field. A simple non-magnetic fluid would not move much because of heat unless there was a phase change involved.
  5. Sep 22, 2012 #4
    It's confusing terminology. Perpetual motion is perfectly OK -- the Earth more or less does this as it orbits the sun, for 9 billion years any way. Superflow is a perpertual flow and is also possible. A perpetual motion machine implies that it is producing more energy than it consumes, which is not possible. So they aren't the same thing.

    In a tokomak there is a lot of energy going in to the electromagnets. It can't be built in such a way as to not lose energy. Pull the plug and it will cool down.
  6. Sep 23, 2012 #5
    sequenced magnetic disturbance + ferromagnetic fluid +torus or spherical shaped design = fun science.
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