RE: starship-design: Staged Fusion Power

["L. Parker" <lparker@cacaphony.net>]

Hi Timothy,

Try this table:

Table I:  Fusion Reactions Among Various Light Elements
D+D   -> T (1.01 MeV) + p (3.02 MeV) (50%)
      -> He3 (0.82 MeV) + n (2.45 MeV) (50%)  <- most abundant fuel
      -> He4 + about 20 MeV of gamma rays (about 0.0001%; depends
                                           somewhat on temperature.)
      (most other low-probability branches are omitted below)
D+T   -> He4 (3.5 MeV) + n (14.1 MeV)  <-easiest to achieve
D+He3 -> He4 (3.6 MeV) + p (14.7 MeV)  <-easiest aneutronic reaction
                                     "aneutronic" is explained below.
T+T   -> He4 + 2n + 11.3 MeVHe3+T -> He4 + p + n + 12.1 MeV (51%)
      -> He4 (4.8) + D (9.5) (43%)
      -> He4 (0.5) + n (1.9) + p (11.9) (6%)  <- via He5 decay

p+Li6 -> He4 (1.7) + He3 (2.3)      <- another aneutronic reaction
p+Li7 -> 2 He4 + 17.3 MeV (20%)
      -> Be7 + n -1.6 MeV (80%)     <- endothermic, not good.
D+Li6 -> 2He4 + 22.4 MeV            <- also aneutronic, but you
                                              get D-D reactions too.
p+B11 -> 3 He4 + 8.7 MeV <- harder to do, but more energy than p+Li6
n+Li6 -> He4 (2.1) + T (2.7)        <- this can convert n's to T's
n+Li7 -> He4 + T + n - some energy

As you can see from the table D+He3 is a good candidate for the second stage
if you use D+D as the first stage and then somehow manage to fuse the He3
produced before it can escape. Of course you also have to worry about
neutrons from the D+D reaction. Too bad we can't use the gamma rays produced
in the D+D reaction though... As you said, your notation is a little
different but it is understandable. Where did you get the 18.4 MeV though?

Notice that most of the reactions in this table produce He4 as a by-product.
My first choice would be a straight single stage D+Li6 or p+B11 using
antimatter catalysis or muon catalysis to start the reaction.

Lee