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-   -   how do TOKAMAK's provide thermal insulation (http://www.physicsforums.com/showthread.php?t=320593)

Ian_Brooks Jun17-09 10:05 PM

how do TOKAMAK's provide thermal insulation
 
For current fusion technology the method for containing the plasma is with magnetic fields. However the plasma reaches temperatures of 100,000 degrees+ that would melt anything on earth -

so how do these super concentrated magnetic field provide thermal insulation?

Monocles Jun20-09 03:54 PM

Re: how do TOKAMAK's provide thermal insulation
 
The plasma reaching such high temperatures is really just because of our macroscopic definition of temperature. A 100 million degree tokamak plasma isnt going to melt stuff the same way a 100 million degree lump of normal material would, it just means that very energetic neutrons will occasionally hit the walls of the reactor. Making a material that can stand such collisions for a long period of time is currently an active area of research.

Astronuc Jun20-09 04:14 PM

Re: how do TOKAMAK's provide thermal insulation
 
Quote:

Quote by Ian_Brooks (Post 2241747)
For current fusion technology the method for containing the plasma is with magnetic fields. However the plasma reaches temperatures of 100,000 degrees+ that would melt anything on earth -

so how do these super concentrated magnetic field provide thermal insulation?

Charged particles move in small circular trajectories around magnetic field lines when their velocities are perpendicular to the magnetic fields. The magnetic fields are imposed on the outside of the plasma, and the plasma excludes the magnetic fields by virtue of the rotating particles producing magnetic fields opposite the fields which cause them to rotate. Therefore the magentic field is lower and the particles (ions and electrons) tend to preferentially move to the interior. Neutral atoms do pass through magnetic fields, but their flux is kept as low as possible.

The plasmas has very low density ~ 1014 ions-electrons/cm3, as compared to solid materials with atomic densities on the order of 1022/cm3. The energy leaking to the confinement chamber is very low.

Energy is also radiated in the form of photons via cyclotron radiation, recombination, and bremsstrahlung, so the first wall needs to be cooled.


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