A CF$_{4}$ based positron trap

All positron buffer gas traps in use rely on N$_{2}$ as the primary trapping gas due to its conveniently placed a$^{1}\Pi $ electronic excitation cross section that is large enough to compete with positronium (Ps) formation in the threshold region. Its energy loss of 8.5 eV is sufficient to capture positrons into a potential well upon a single collision. The competing Ps formation, however, limits the efficiency of the two stage trap to 25 {\%}. As positron moderators produce beams with energies of several eV we have proposed to use CF$_{4}$ in the first stage of the trap, due to its large vibrational excitation cross section, where several vibrational excitations would be sufficient to trap the positrons with small losses. Apart from the simulations we also report the results of attempts to apply this approach to an existing Surko-type positron trap. Operating the unmodified trap as a CF$_{4}$ based device proved to be unsuccessful, due primarily to excessive scattering due to high CF$_{4}$ pressure in the first stage. However, the performance was consistent with subsequent simulations using the real system parameters. This agreement indicates that an efficient CF$_{4}$ based scheme may be realized in an appropriately designed trap.