I wonder if there is a way to stabilize and store positronium in a way that the mass of storage device is negligible to the antimatter fuel
It is known that excited Ps atoms with high n (rydberg or rydberg-like) have estimated lifetimes of the order of years. Since positronium seems to be quite reactive (di and tri-positronium molecules have already been observed) I've been wondering if it could be possible to grow large crystals from positrons and electrons in a simple cubic lattice, where Na and Cl in the lattice being replaced by $e^{+}$ and $e^{-}$.
Question: is possible that positronium can have a crystalline bulk phase with enough ion distances to avoid annihilation?
The reason why I'm interested in positronium and not antihydrogen, which looks relatively easier to manipulate, is that proton-antiproton annihilation is extremely messy, with more than half of the mass-energy decaying into end products like neutrinos, which won't contribute anything to kinetic energy. In contrast, positronium decays in relatively soft gamma rays of 511 KeV (and 380 KeV for orthopositronium) that in theory we could reflect with extremely low grazing angles with efficiencies up to 90%
As an addendum to the larger question of positronium storage methods, I can't avoid mentioning that there have been other ways proposed over the years to keep the antimatter from touching the walls. If we want to store positron and electron separated, we have to deal with the Brillouin density limit that affects all existing and future Penning traps ($10^{12} e/cm^{3}$ for a field of 1 Tesla), so a simple calculation shows that a cylindrical container with weight ratio of 1 between container and antimatter masses, with 100 Tesla and 10 cm of thickness will have to have a radius of $10^{12}$ meters, roughly the radius of Neptune orbit! so in order to explore more viable alternatives, we are forced to consider only neutral antimatter (unless we find materials able to sustain over large regions magnetic fields 5-6 orders of magnitude higher than the current state of the art)
This report gives a nice overview of some of the alternatives that have been explored, the most interesting is paraelectricity (which is an effect where induced electric fields create virtual mirror charges on the wall that repels charges and possibly dipoles). Quantum reflection between antimatter BEC and wall is also mentioned, but I have reservations toward this one, since even if positronium BEC will form theoretically at higher temperatures (roughly 1-10 Kelvin), it is still complex to keep a large mass of BEC isolated enough from the environment (think of accelerations on a hypothetical ship) to make this a viable alternative. Basically if you sneeze, you and your ship will become a mininova.
There is one patent online proposing using photonic bandgap crystals to disallow the decay band of Rydberg positronium, but it seems to me that requires cavities that are of the order of one wavelength of the decay radiation, which put us again in a scenario with low ratios of container-fuel masses
PS: Glad I've finally written this down, hopefully I'll be able to take my mind off a bit from this subject
Best Answer
Practically speaking there is currently no way to stabilize and store positronium in a way that the mass of storage device is negligible to the antimatter fuel. If you are pioneering this research I recommend investigating the face centered cubic crystal lattice structure as a first choice.