A new high field spectrometer has been built to extend the capabilities of the β-detected nuclear magnetic resonance ( β-NMR) facility at TRIUMF. This new beamline extension allows β-NMR spectroscopy to be performed with fields up to 200 mT parallel to a sample’s surface (perpendicular to the ion beam), allowing depth-resolved studies of local electromagnetic fields with spin polarized probes at a much higher applied magnetic field than previously available in this configuration. The primary motivation and application is to allow studies of superconducting radio frequency (SRF) materials close to the critical fields of Nb metal, which is extensively used to fabricate SRF cavities. The details of the design considerations and implementation of the ultra-high vacuum (UHV) system, ion optics, and beam diagnostics are presented here. Commissioning of the beamline and spectrometer with radioactive ions are also reported here. Future capabilities and applications in other areas are also described.

We report depth-resolved measurements of the Meissner screening profile in several surface-treated Nb samples using low-energy muon spin rotation. In these experiments, implanted positive muons, whose stopping depths below Nb's surface are adjusted between approximately 10 nm and 150 nm, reveal the field distribution inside the superconducting element via their spin precession (communicated through their radioactive decay products). We compare how the field screening is modified by different surface treatments commonly used to prepare superconducting radio-frequency cavities used in accelerator beamlines. In contrast to an earlier report [A. Romanenko et al., Appl. Phys. Lett. 104, 072601 (2014)], we find no evidence for any "anomalous" modifications to the Meissner profiles, with all data being well described by a London model. Differences in screening properties between surface treatments can be explained by changes to the carrier mean free paths resulting from dopant profiles near the material's surface.