XPost: sci.energy.hydrogen, sci.physics.fusion   
   From: dietz@dls.net   
      
   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.   
      
      
   > 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).   
      
   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.   
      
   	Paul   
      
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