Cryogenic Positron-beam System for Atomic Physics

Trapped positron plasmas are routinely used to generate beams that can be used for a wide variety of experiments, such as studies of positron annihilation on molecules.\footnote{Gribakin, Young, and Surko, {\it Rev. Mod. Phys.} {\bf 82}, 2557 (2010).} While current beam generation techniques are sufficient, for example, for the measurement of positron-molecule binding energies, more detailed studies are limited by beam energy resolution. Described here is a new method of positron beam formation using a buffer gas cryogenically cooled to 50 K. Simulations of the beam formation process\footnote{Natisin, {\it et. al.}, AIP Conf. Proc. {\bf 1521}, 154 (2013).} are discussed and used to predict an energy resolution of $\approx 9$ meV FWHM; a factor of 5 improvement over current techniques. Various possible physical measurements using this technique are discussed, including the ability to resolve individual vibrational mode features in the molecular annihilation spectra.\footnote{Jones, {\it et. al.}, {\it Phys. Rev. Lett.} {\bf 110}, 223201 (2013).}