The Surko buffer-gas-trap and generation of high-resolution positron beams.

The Surko buffer-gas-trap (BGT), based on the Penning-Malmberg trap, has been highly effective in generating pulse, high-energy resolution positron beams for wide range of studies, including atomic and molecular scattering, annihilation processes, antihydrogen production, and positronium formation [1,2]. The trap obtains positrons from a ²²Na radioisotope source and solid Ne moderator. A three stage buffer-gas-trap facilitates efficient trapping and cooling at room temperature through inelastic collisions with molecular gases N₂ and CF₄. The positron beams are then extracted from the trap by careful control of the confining potentials, with ultimate energy resolution of △ε ≃ 40 meV and time width of △t ∼ 2 µsec. The current UCSD setup has an additional cold trap with CO as buffer gas and can give an enhanced beam resolution of △ε < 20 meV [3]. The BGT traps have been employed in a wide range of positron-matter annihilation studies, providing high-resolution beams for positron binding energy measurements, annihilation spectral analysis, positronium studies, materials science, astrophysics, and many other applications [4,5] to be discussed.

[1] C. M. Surko et al., J. Phys. B: At. Mol. Opt. Phys. 38, R57 (2005).

[2] G. F. Gribakin et al., Rev. Mod. Phys. 82, 2557 (2010)

[3] M. R. Natisin et al., Appl. Phys. Lett., 108, 024102 (2016)

[4] D. B. Cassidy, Eur. Phys. J. D 72, 53 (2018)

[5] J. R. Danielson et al., Rev. Mod. Phys. 87, 247 (2015)