Delivering hydrogen ions for use in precision matter / antimatter experiments The University of Manchester in United Kingdom

The ALPHA experiment at CERN performs precision atom physics experiments on trapped antihydrogen, having performed numerous first measurements on this exotic antimatter including the first measurement of the gravitational eIect on anti-atom motion and the first lineshape measurement of the 1S – 2S atomic transition [1,2]. Achieving the highest level of precision with these measurements will require direct comparison of hydrogen and antihydrogen measurements in the same machine. To this end, ALPHA is planning an ambitious campaign for developing equivalent hydrogen / antihydrogen measurements in its experiments. The first step in performing such measurements is the creation of trapped H atoms for use in experiments. The project proposes to develop a H-production based on recombination with protons in a manner which is inverse to the typically antihydrogen production used on ALPHA or threshold photodissociation of H-minus ions and subsequent magnetic trapping. The scheme utilises the ALPHA beamline infrastructure designed and developed by UoM / Cockcroft / RAL to guide hydrogen ions produced by a custom PELLIS ion source developed for ALPHA through collaboration of UoM, CI, RAL, ASTEC, JYFL [3,4]. The project first requires an additional beamline station to decelerate and transport the hydrogen ions to the existing ALPHA traps in order to trap proton and Hminus plasmas in Malmberg-Penning traps for use in hydrogen formation and trapping experiments.

Proposed Scheme of Work

The successful student project will aim to establish the first hydrogen production and trapping in the ALPHA experiment. The project includes simulation work to optimize the production, transport and capture of these ions in the ALPHA penning traps. Additionally, the project will explore requirements for an antiproton buncher to maintain the present beamline functionality with this additional ion source station. They will also help design and ultimately install and commission the source and beamline infrastructure at CERN. Further, they will carry out an experimental campaign to optimize transport, capture, manipulation and cooling of these ions in ALPHA, including sympathetic cooling techniques with positron and electron plasmas. The student will also aid in the design of hydrogen formation experiments, including detection schemes, and be uniquely positioned to perform the first hydrogen re-combination experiments in ALPHA. If successful, this would be the first production and use of a trapped H-minus plasma for fundamental physics measurements, as well as a serve as a novel laboratory source of hydrogen.

[1] ALPHA Collaboration, “Observation of the eIect of gravity on the motion of antimatter” Nature volume 621, pages 716–722 (2023)

[2] ALPHA Collaboration, “Characterization of the 1S–2S transition in antihydrogen” Nature volume 557, pages 71–75 (2018)

[3] ALPHA Collaboration, “Design and performance of a novel low energy multispecies beamline for an antihydrogen experiment” Phys. Rev. Accel. Beams 26, 040101 (2023)

[4] M.A. Johnson et al “Development and commissioning of a hydrogen ion source for the CERN ALPHA experiment” 2024 JINST 19 C01021