Positronic Fuel Safer?

pete wrote:

Well, if you collect positrons
in a trap, while adding electron charge to the housing, it might work...

You *could* store a neutral electron/positron plasma, but for a useful
lifetime the density must be very low. This might be useful in space,
where a very large but dilute plasma could be stored in a dipole
magnetic field (say). Since for non-relativistic e-/e+, the annihilation
cross section is inversely proportional to velocity, the rate of
annihilation will be independent of the temperature of the plasma.
And, since the mass of the magnet is proportional to the stored magnetic
energy, which in turn (at fixed beta) is proportional to plasma
pressure, you want as cold a plasma as you can get, down the
point where the magnetic field is too weak to remain substantially
unaffected by the solar wind.

Positronium in excited states would also be useful for making
antihydrogen, since the reaction

pbar + positronium* -- Hbar* + e-

conserves energy and momentum without the need for emission
or absorption of a photon.

Paul