Phase-space dynamics of metastable helium atoms in a 180-degree semicircular magnetic hexapole guide

Metastable helium (He) atoms travelling in pulsed supersonic beams have been magnetically transported through a 180-degree semicircular magnetic hexapole guide. This device had a radius of curvature of 0.6 m. The supersonic beam discharge source used to generate the metastable He was operated at a temperature of 35 K, resulting in beams with mean longitudinal speeds of ~600 m/s. The magnetic guide into which these beams were injected comprised sixty-one 25-mm-long permanent magnet Halbach arrays, mounted on a curved rail. These arrays had an open inner diameter of 6 mm. Atoms transmitted through the guide were detected using a time-gated position-sensitive microchannel plate detector. This enabled the measurement of longitudinal and transverse phase-space properties of the transported beams, which are in good quantitative agreement with the results of numerical particle trajectory calculations. In addition to operating efficiently to transport metastable He, this device is also suitable for magnetic transport of atomic hydrogen isotopes, e.g., H, D, and T. Integration in the future with a second similar 180-degree section could enable the realization of a magnetic storage ring for these species. The confinement of cold high-purity gases of T atoms in a storage ring of this kind, is of interest for next generation laboratory measurements of the absolute neutrino mass [1-3].

[1] B. Monreal and J. A. Formaggio, Phys. Rev. D 80, 051301(R) (2009)

[2] A. A. Esfahani et al., J. Phys. G: Nucl. Part. Phys. 44, 054004 (2017)

[3] A. A. S. Amad et al., New J. Phys. 27, 105006 (2025)