Speaker
Description
Positron and proton sources, and traps have played a pivotal role for the antimatter research taking place both in Vienna and at CERN as part of the ASACUSA collaboration.
At home in Vienna, we have designed and constructed a positron beamline which uses a conventional $^{22}$Na source and Ne moderator to produce a beam which is trapped and conditioned for experiments in a Surko-type positron trap [e.g. 1,2]. This beamline is currently being commissioned after final safety clearances for operation to use the source in a residential area. We first aim to use the positron pulses from this trap to observe molecules containing positronium, such as PsH [3] and PsO [4] via collisions in gases such as methane and carbon dioxide. By using a high-resolution ion mass spectrometer to detect fragments from dissociation, a precise measurement of their binding energy will be performed.
We have also designed, built and characterised a proton source [5] for the ASACUSA collaboration with the aim of performing matter mixing experiments when antiprotons are not available. Using electron impact ionisation, protons are created via dissociative ionisation of H$_2$ gas. A rotating wall electric field destabilises the unwanted H$_2^+$ and H$_3^+$ generated during the dissociative ionisation process, while concentrating the protons in the centre of the trap. The source produces bunches of protons with relatively low ion contamination (5.5 % H$_2^+$ and 15.5 % H$_3^+$), with energy tuneable from 35 to 300 eV, and has already been used to transfer protons into the ‘Cusp’ trap at CERN.
[1] J. P. Sullivan, A. Jones, P. Caradonna, C. Makochekanwa, and S. J. Buckman , "A positron trap and beam apparatus for atomic and molecular scattering experiments", Review of Scientific Instruments 79, 113105 (2008).
[2] J. Clarke, D.P. van der Werf, B. Griffiths, D.C.S. Beddows, M. Charlton, H.H. Telle, P.R. Watkeys, Design and operation of a two-stage positron accumulator, Review of Scientific Instruments. 77, 063302 (2006).
[3] D.M. Schrader, F.M. Jacobsen, N.-P. Frandsen, U. Mikkelsen, Formation of positronium hydride, Phys. Rev. Lett. 69 (1992) 57–60.
[4] X. Cheng, D. Babikov, D.M. Schrader, Binding-energy predictions of positronium-atom systems, Phys. Rev. A. 85 (2012) 012503.
[5] A. Weiser, A. Lanz, E. D. Hunter, M. C. Simon, E. Widmann, D. J. Murtagh; A compact low energy proton source, Review of Scientific Instruments 94, 103301 (2023)
