Recent Developments and Future Plans for the Accelerator Based Slow Positron Facilities at AIST

Abstract

We describe the recent installation of a new slow positron beamline at AIST and our plans to develop a dedicated superconducting accelerator for positron production. The new positron beamline is already installed and should be operational by the end of this fiscal year (March 2012). Initially positrons will be generated using a 70 MeV electron beam from the existing accelerator directed onto a newly installed converter and moderator assembly. The beamline has two experimental ports both dedicated to positron lifetime spectroscopy, one port with a focused beam (diameter ~ 30 microm) and the other unfocussed (~ 10 mm). A superconducting accelerator for positron production is currently under development. When completed, it will deliver a high frequency (~ MHz), high current (~ mA), short pulse length (< 100 ps) beam to the positron production target. We investigate the possibility of transporting the positron pulses thus produced directly onto samples for lifetime measurement. Such a scheme would remove the necessity for pulse stretching and chopping which is required with the existing LINAC and should allow for greatly increased slow positron transport efficiency.