XPost: sci.energy.hydrogen, sci.physics.fusion   
   From: g_d_pusch_remove_underscores@xnet.com   
      
   "Paul F. Dietz"  writes:   
      
   > Gordon D. Pusch wrote:   
   >   
   >> Unfortunately, we do =NOT= have the _FAINTEST_ clue as to how to build   
   >> a fusion reactor that could burn the stuff without a net _LOSS_ of energy.   
   >> It takes temperatures and plasma densities more than an _ORDER OF MAGNITUDE   
   >> HIGHER_ than D/T fusion to "ignite" even the "easiest" He3-burning reaction,   
   >> and it is not clear that such a reactor could =EVER= "break even," since   
   >> its bremsstrahlung loss rate likewise exceeds its energy generation rate   
   >> by more than an order of magnitude. Trying to "burn" He3 is like trying   
   >> to burn soaking wet paper --- it costs more heat than you get out of it.   
   >   
   > Where does this 'exceeds its energy generation rate by more than an order   
   > of magnitude' come from?  The ideal situation I recall (optimal plasma   
   > conditions, 'hot ion mode') was 19% of the energy goes into bremsstrahlung.   
      
   That's not what I remember from Art Carlson's (sadly defunct) webpage   
   summarizing the Rider Thesis. What I remember was that bremsstrahlung   
   losses exceed energy generation by a factor of 15; I will have to dig out   
   the copy of the Rider Thesis Jim Logajan kindly loaned me and see if I can   
   find the exact figure, but I'm pretty sure that a factor of 15 is correct.   
      
   Note also that one of Rider's main claims was that fancy "non-equilibrium"   
   concepts such as "hot ion mode" don't work: =ALL= "reactor-type" fusion   
   plasmas relax to thermodynamic equilibrium FAR faster than they generate   
   fusion energy, and attempts to _keep_ them far from equilibrium will   
   always cost more additional energy than they will produce.   
      
      
   >> Furthermore, it would be cheaper to _MANUFACTURE_ He3 on the Earth by   
   >> "breeding" Tritium and waiting for it to decay than to mine it on the   
   >> Moon and ship it back to Earth. So quite bluntly, this lunatic idea   
   >> is pure moonshine.   
   >   
   > A contained, underground 1 MT explosion could produce several kilograms   
   > of tritium (and ultimately 3He).   
      
   If you're willing to do that, then you might as well go whole hog and build   
   a PACER system for power generation --- but not in _my_ backyard !!!  >8-(   
      
      
   > The biggest problem with lunar 3He is that the energy required to extract   
   > it from the regolith is substantial; even if this energy does not exceed   
   > the fusion energy content of the gas, it will be a significant fraction   
   > of it.  You don't want to have to build a 100 MW powerplant on the moon   
   > in order to fuel a 1 GW powerplant on earth; the cost of the former would   
   > dwarf the cost of the latter.   
      
   Agreed.   
      
      
   -- Gordon D. Pusch   
      
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