Positron and Positronium

A snapshot of the pulsed positron beam. The flagship of the LPPP and motor for various high precision low energy positron and positronium experiments. The long cylinder is a buffer gas trap which allows to store large amounts positrons and emits spatially collimated positron bunches of short duration and little energy spread. On the left the laser excitation chamber for positronium spectroscopy is visible.

The Laboratory for Positron and Positronium Physics facility consists of two low energy positron beamlines operating in the 0-20 keV energy range. The first is a continuous beam with a secondary electron tagging system and time buncher, and is equipped with a positron annihilation lifetime spectrometer, high purity Ge detector for Doppler broadening spectroscopy, and fast sample changeover capabilities for material science studies. In addition, this beamline is also used to supply tagged positrons for the EPIC experiment, searching for invisible decays of positronium, and was used in recent positronium laser spectroscopy measurements.

The second beamline is a pulsed mode beam, capable of delivering short (~1 ns), intense positron pulses to a target in an electromagnetic field-free chamber. The pulses are generated using a buffer gas trap technique, where positrons are confined in a potential well through inelastic scattering with a gas, and then periodically released. This beamline is equipped with a time buncher, single gap accelerator and various scintillating detectors and beam profiling detectors. It is used in ongoing positronium spectroscopic studies.