Rare gas moderated electrostatic positron beam

Abstract

An electrostatically guided positron beam which is variable in energy from 0 to 60 keV is described. A frozen inert gas (Ar, Kr, and Xe) is used as the positron moderator. The efficiency, ε, defined as the ratio of the number of slow positrons at the target to the number of positrons emitted by the source has been measured; the values obtained for Ar, Kr, and Xe were ε∼ 2.5×10−4, 1.6×10−4, and 1.1×10−4, respectively. We estimate a source/moderator efficiency of εm∼7.6×10−4, 4.7×10−4, and 3.0×10−4 for Ar, Kr, and Xe, respectively, which includes source effects, grid transmission, geometrical losses, and beam transport. These values are comparable to the best reported values for thin metal foil moderators. The measured εm is specific to the electrostatic system; significantly higher values for the same moderator should be attainable in magnetically guided beams, where higher transmission for moderators with large energy spreads is usually obtained.

Experimental progress in positronium laser physics

“…45. Ps BEC critical temperature as a function of density as given by equation (55). Also indicated is the density at which Ps-Ps interactions have been observed, and the approximate Ps laser cooling recoil limit.…”

“…In 1986 the solid neon moderator was introduced [53], and this methodology still underpins the state-of-the-art in slow positron beam production using radioactive isotopes today [54][55][56][57][58][59][60][61]. The availability of positron beams has facilitated a great deal of work on experimental atomic positron and Ps physics [62][63][64][65], and positron-gas scattering measurements have informed the development of positron buffer-gas traps [66][67][68][69].…”

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

“…After the moderation, slow positrons will be extracted from the moderator by electrostatic 43 or magnetic 44 focusing methods depending on the experimental needs. As it is known that the energy bandwidth of the emitted slow e + from an RGM is higher than a W moderator, the resulting beam brightness will be lower but the brightness can be significantly enhanced with brightness enhancement methods to develop a positron microprobe.…”

Antimatter plasmas and antihydrogen

“…Neon has the highest moderation efficiency, although argon, krypton, and xenon perform reasonably well. 91,93 We have recently demonstrated the use of a two-stage refrigerator for the production of neon moderators, 94 which require temperatures of Ͻ8 K. This results in a considerable cost-saving over the three-stage units that were previously required to reach this temperature. Moderation efficiencies ͑as defined above͒ of about 0.006 are commonly obtained for krypton and neon.…”