[ RadSafe ] Tokomak, Fusion, etc.

[JPreisig at aol.com]

Hmmmmmm,

     This is from:    jpreisig at aol.com     .

      Howdy Radsafers,

           As usual, Franz is the demanding one and wants to hear about 
      tokomaks, fusion and the like.  OK, I will try to comply briefly.
      A fairly recent book with fusion discussions is Emilio Segre's book
      on Nuclear  and Particle Physics.  

           Tokomaks are ring-like structures (a torous or donut shape) which 
use magnetic fields to contain the eventual hot plasma gas.  The NSTX at 
Princeton
(PPPL) is like a tokomak whose outside radius has been shrunk so that
the donut shape approaches a more spherical torous shape.

          The basic fusion reactions are deuterium on deuterium and/or
   deuterium on tritium.  The second reaction produces 15 MeV
   neutrons.  These 15 MeV neutrons can interact with the fusion reactor
   assembly (metals and other materials) and neutron activate such
   materials.  Such neutron activation is described in the book Accelerator
   Health Physics by Patterson and Thomas and in a more dedicated book on
   activation, which is probably listed in Patterson & Thomas' references.

         The energies to make the fusion reactions go is typically 10 to 50
   keV.  So, if you put in 10 to 50 keV and can get 15 MeV out (via the
   neutrons), then you gain energy by making fusion reactions happen.
   You have to contain the fusion plasma with magnetic fields or else the 
    plasma will interact with the fusion reactor (material) walls and destroy 
the
    fusion reactor structure.

          The TFTR at PPPL was a tokomak of sorts, I believe.

         You can breed tritium by allowing the fusion neutrons to interact 
with a
    blanket of Lithium, as alluded to by other persons posting to radsafe.

          The fusion reaction must achieve a sufficient temperature for the 
    reaction to go, and must have a density of D and T ions sufficient to 
    have a significant number of fusion reactions occur.  Also one wants to 
    keep the plasma "together" for a useful amount of time to get net energy
    out.  If the D and T particles are indeed ions, then these ions repell
    each other electromagnetically.

          Clearly  D,T fusion occurs all the time in neutron generators.  But 
    the reaction is not occuring on a large (spatial) scale.

          Tokomaks work to confine plasmas because plasmas leaking from
    one section of the tokomak leak only into other regions of the tokomak.
    The fusion reaction is always contained by magnetic fields.

          On and On,  Blah, Blah, Blah.

         The deutrium for the fusions was supposed to come from ocean
water.  As stated earlier, tritium can be bred in a fusion reactor.

          Franz, if you have more specific questions, just ask them and I will
   try to answer.  If the question is beyond me, I will just say so.

          Regards,             Joseph R. (Joe) Preisig,  Ph.D.