Re: Fusion

The quoted bits are all taken (without permission) from ``Nuclear Fusion''
by Keishiro Niu (pub. CUP)...

``
         1          4
        4 H +2e   =  He + 27.05 Mev
         1          2                   (with a 7% mass decrease)

  The sun continuously shines because of this nuclear fusion.  However
from a small power station on earth (by contrast to the giant sun) the
fusion energy released cannot be obtained because of the very low reaction
rate.''

This reaction has a slow rate (10e-24 of the ``cross-section'' of the
Deuterium-Deuterium reaction) because of the small chance of a colliding
proton decaying into a neutron + positron + neutrino.   But maybe Traveller
fuel plants could use this reaction with the aid of a nuclear damper in decay
rate increase mode ?

Keishiro then goes on to describe three ``generations'' of fusion reaction
(each requiring higher temperatures).

1st Generation:
``      2    3     4     1
         D +  T =   He +  n   + 17.6MeV
        1    1     2     0
has the greatest possibility of being utilised.''

``The half life of T is 12 years so none exists naturally.''
But it can be synthesised as an intermediate stage of
        6    2     4
         Li + D = 2 He + 22.4 MeV
        3    1     2

[Lithium has never been mentioned in conjunction with trav plants, so scratch
this one].

2nd generation:
``Hydrogen found on earth includes Deuterium in the mass ratio of 1:5000''

                   3     1
                    He + n + 3.27MeV
                   2     0
        2    2
         D +  D =     OR [with about even probability]
        1    1
                   3    1
                    T  + H  + 4.03MeV
                   1    1

``An oilcan full of heavy water will supply enough energy to run a car for a
lifetime if the car has a fusion engine.''

Yup !  Looks like Trav fusion engines are massively inefficient.
This reaction also outputs neutron radiation and the evil radioactive hydrogen
isotope tritium: half life 12 years, diffuses through anything, gets into
water, organic compounds, YOU!

3rd generation reactions:
``
        1    11       4
         H +   B  =  3 He + 8.7MeV
        1     5       2

        1     6       3    4
         H +   Li =    He + He + 4.0MeV
        1     3       2     2
''
Nice because it outputs nothing but helium (but requires Lithium and/or
Boron again, so forget this one for Trav).


Effieciency of Trav power plants
- - ---------------------------------
The prescence of neutrino detectors in MegaTrav, and the fact that 1 ton of
gas giant atmosphere from your refuelling shuttle can be refined
into 1 ton of fuel, not just 0.2kg of Deuterium, is strong evidence that the
proton-proton reaction is somehow used in Trav power plants.
The reactor will probably incorporate sort of weak-interaction rate
increaser (a nuclear damper related device or other handwaving).

1MeV = 1.6e-13 Joules

Avogadro's Number: 6e23 per mole

          1 2
1 Mole of  H  weighs 0.002kg
          1

          1 2
1 Mole of  H  releases 0.5 * 6*10^23 * 27.05*1.6*10^-13 = 1.3*10^12 J
          1

          1 2
1 Ton of   H  releases 1000/0.002 * above = 6.6*10^17 J
          1

Striker
- - -------
  A TL15 fusion plant outputs 6MW, using 1.5l/hour fuel.
  1l fuel weighs 0.07kg = 7*10^-5 tons.
  Energy out (according to book) = 6*10^6 * 3600             = 2.2*10^10 J
  Energy out if 100% efficient   = 1.5 * 7*10^-5 * 6.6*10^17 = 6.9*10^13 J
  => Efficiency 0.032%    (about 0.01% at TL9).

MegaTraveller
- - -------------
  A (large enough) TL15 reactor outputs 18MW using 9l/hour.
  This is 3 times as much as a Striker reactor, but needs 6 times as much fuel
  => Efficiency 0.016%

TL16 plants are marginally better.  And then at TL17 antimatter plants appear
(Hmm... wonder why there aren't many TL17 planets around :^)

If Trav plants were using the D-D reaction, they would be 7.4 times
more efficient... about 0.25%.

You can think of any number of excuses for poor inefficiency.  Just how
do you extract useable energy from a fusion reactor anyway ?  Apparently it is
somehow theoretically possible to extract electric current directly; this would
be so useful you might not be too bothered about efficiency.
Current power stations need huge amounts of cooling water.  Can you radiate
off waste heat fast enough from a small starship ?  Possibly the vast majority
of the fuel (99.984%) is just vented off as cooling.

It's a shame there isn't a bit more variety in Trav fusion plants over the
tech levels, especially considering that low tech chemical fuel power plants
about double in efficiency every two tech levels.

+-----------------------------------------------------------------------------+
  Tim Day        [email removed]       | If I knew how starship drives really
  Department of Insanity and Surveying | worked, I'd be writing to the patent
  [address removed]                    | office, not the Traveller mailing list
+-----------------------------------------------------------------------------+

PS Orca's original 0.0000002% was based on H-H fusion being 4*10^6 times better
than it really is due to c being wrong, and the calculated energy release
should have been per 4 moles of H, which corrects it to  0.8% efficiency.
Where did you get the amount of fuel used from ?  Are maneuver drives more
efficient than power plants ?