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

Abstract

We present a conceptual design for a novel continuous wave electron-linac based high-intensity high-brightness slow-positron production source with a projected intensity on the order of 10 10 e + /s. Reaching this intensity in our design relies on the transport of positrons (T + below 600 keV) from the electron-positron pair production converter target to a low-radiation and low-temperature area for moderation in a high-efficiency cryogenic rare gas moderator, solid Ne. This design progressed through Monte Carlo optimizations of: electron/positron beam energies and converter target thickness, transport of the e + beam from the converter to the moderator, extraction of the e + beam from the magnetic channel, a synchronized raster system, and moderator efficiency calculations. For the extraction of e + from the magnetic channel, a magnetic field terminator plug prototype has been built and experimental results on the effectiveness of the prototype are presented. The dissipation of the heat away from the converter target and radiation protection measures are also discussed.

Proposal for a slow positron facility at Jefferson National Laboratory

“…There was some concern expressed by the attendees that there is a long path from 100 MeV to 1 eV and while many have attempted it, none have succeeded in getting 10 10 slow e + /s in a useful beam diameter and energy. This concern was met by consideration of the proposal from NCCU [17] of a way to use the highly efficient solid Ne moderator [8] to get slow positron intensities much greater than 10 10 slow e + per sec. Another concern was that the Jefferson Lab has no onsite history, expertise, or leadership in slow positron physics.…”

“…(1) The primary solid Ne moderated slow positron source will be based on the proposal by S. Golge, B. Vlahovic, and B. Wojtsekhowski [17] and will be implemented by collaborators at JLab.…”

Project for a Source of Polarized Slow Positrons at ELI-NP

“…Bright γ-sources from electron bremsstrahlung in a target or from nuclear reactors are used successfully to generate intense positron beams (for a review of the positron sources worldwide see [3]). Spin-polarized positrons from radioactive sources provide a new, atomic scale view on the magnetism and electronic structure of magnetic materials [4].…”