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How do magnetic fields provide thermal insulation

  1. Jun 18, 2009 #1
    some Fusion power experimental reactors use tokamaks to contain plasma using strong magnetic fields. However this plasma is at a sizzling 1M Kelvin so how is this level of thermal insulation engineered, using magnetic fields?
     
  2. jcsd
  3. Jun 18, 2009 #2

    mgb_phys

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    The magnetic field doesn't provide insulation it simply holds the electrically charged plasma away from the walls.
    Heat isn't the same as temperature, the sparks from a sparkler are at >1000 deg C but don't contain very much heat.
     
  4. Jun 18, 2009 #3
    The plasma is primarily ionized particles. The Lorentz force is
    F = q(E + v x B)
    where q is particle charge, v is particle velocity, and B is magnetic field. The v x B term causes the ionized particles to move in orbits perpendicular to the magnetic field, similar to ions in a cyclotron.
     
  5. Jun 18, 2009 #4
    then what stops the core from melting? i'm certain plasma would be quite hot
     
  6. Jun 18, 2009 #5
    What stops the core from melting is that heat doesn't transfer at a high enough rate form the plasma to the core. Convective and conductive heat require a medium for transport. I'm not sure about the magnitude of radiative heat transfer from plasma though but I would assume the walls of the reactor would have a very low emissivity.
     
  7. Jun 18, 2009 #6

    mgb_phys

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    The tokamak is a donut shape. The plasma is in a ring inside the donut in a very high vacuum it doesn't (ideally) touch the inner or outer walls.
     
  8. Jun 18, 2009 #7
    Strong magnetic field provides physical separation of the plasma tore and TOKAMAK walls. Plasma itself at these densities and temperatures is not quite transparent for the "light" - it radiates mostly from its surface.

    Bob_for_short.
     
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