How do magnetic fields provide thermal insulation

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Discussion Overview

The discussion centers around the role of magnetic fields in providing thermal insulation in fusion power experimental reactors, particularly in tokamaks, where plasma is contained at extremely high temperatures. Participants explore the mechanisms of heat transfer and the engineering challenges involved in maintaining the integrity of reactor walls.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that magnetic fields in tokamaks contain plasma by holding it away from reactor walls, rather than providing thermal insulation.
  • Others argue that heat transfer mechanisms, including convective and conductive heat transfer, require a medium, which is absent in the vacuum of the tokamak.
  • A participant mentions the Lorentz force and its effect on ionized particles, suggesting that the motion of these particles is influenced by the magnetic field.
  • Concerns are raised about the potential for the reactor core to melt due to the high temperatures of the plasma, questioning how heat transfer is managed.
  • It is noted that the plasma does not ideally touch the walls of the tokamak, which may contribute to thermal management.
  • One participant suggests that the plasma radiates heat primarily from its surface, indicating that the emissivity of the reactor walls plays a role in heat transfer dynamics.

Areas of Agreement / Disagreement

Participants express differing views on the role of magnetic fields in thermal insulation, with some emphasizing the containment aspect and others discussing heat transfer mechanisms. The discussion remains unresolved regarding the specifics of how thermal insulation is achieved in this context.

Contextual Notes

There are limitations in understanding the magnitude of radiative heat transfer from plasma and the specific emissivity of reactor walls, which may affect the overall discussion on thermal insulation.

Ian_Brooks
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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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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.
 
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.
 
then what stops the core from melting? I'm certain plasma would be quite hot
 
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.
 
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.
 
Ian_Brooks said:
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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