How do magnetic fields provide thermal insulation


by Ian_Brooks
Tags: fields, insulation, magnetic, provide, thermal
Ian_Brooks
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#1
Jun18-09, 03:52 AM
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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?
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mgb_phys
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Jun18-09, 08:13 AM
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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.
Bob S
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Jun18-09, 10:29 AM
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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.

Ian_Brooks
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Jun18-09, 10:53 AM
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How do magnetic fields provide thermal insulation


then what stops the core from melting? i'm certain plasma would be quite hot
Topher925
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Jun18-09, 11:12 AM
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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.
mgb_phys
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Jun18-09, 11:15 AM
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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.
Bob_for_short
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#7
Jun18-09, 11:16 AM
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Quote Quote by Ian_Brooks View Post
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?
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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