Research, development and commissioning of a novel bitter-coil quadrupole for atomic fountain studies at TRIUMF

While studying the fundamental building blocks of the universe, high precision is required to characterise matter and antimatter systems, such as hydrogen and antihydrogen. On-going experiments, such as ALPHA at CERN, have measured antihydrogen energy levels to high precision, and started probing gravitational properties of antimatter. However, it is likely that these experiments will eventually be limited by systematic errors, prompting the question: how can these measurements be improved? The Hydrogen-Antihydrogen Infrastructure at Canadian Universities (HAICU) aims to address this by employing quantum sensing techniques, such as Raman and Ramsey interferometry. These approaches have the potential to offer superior precision and help reduce systematic uncertainties. A key goal of HAICU is to implement atomic fountain techniques, which enable high-precision measurements in near-zero magnetic field regions. Hydrogen is initially used as a proxy to demonstrate the feasibility of these methods for antihydrogen. Realising such a fountain system requires sig nificant research and development, particularly for the magnetic minimum trap. To this end, a novel Bitter-coil–based magnet system is being developed. Unlike traditional superconducting magnets, this design offers improved optical access and operational robustness, without the need for cryogenic systems. At the core of the trap is a quadrupole composed of four identical packs, which radially confine cold (< 50 ms-¹) hydrogen atoms. These quadrupole packs operate alongside axial coils to shape the magnetic field geometry for capturing and cooling hydrogen atoms. As part of the R & D effort, a single quadrupole pack was constructed and subjected to extensive testing, including an 8-hour thermal load trial and magnetic field mapping. The pack sustained a stable field of (127.8 ± 6.4) mT at 15 mm from its surface, with temperature increases of (2.9–4.6◦C) relative to the inlet water, under a 1200 A current. These results matched simulation predictions and set the benchmark for the remaining packs. This work establishes a robust testing framework and construction standard for the phase 1 magnetic minimum trap, in coordination with the axial coils, Zeeman decelerator, and detection systems

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