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Abstract

This thesis reports the implementation of a new spectrometer, which extends the capability of TRIUMF 𝛃-NMR facility with fields up to 200 mT parallel to the sample surface. The spectrometer is designed to allow nm-scale depth-resolved studies of superconducting RF (SRF) materials up to the critical field of Nb, the main material for SRF cavities. SRF cavities are the main technology behind high-energy and high-power linear accelerators worldwide. The accelerating electric fields along the cavity axis are accompanied by the radio frequency (RF) magnetic fields parallel to the cavity wall, which induce dissipation due to the penetrating magnetic fields within ~100 nm of the cavity surface. The ability of the SRF materials to screen magnetic fields and the maximum field limit are very sensitive to surface treatments. The magnetic field-dependent surface dissipation affects the operational cost of SRF cavities, and the maximum magnetic field that can be sustained ultimately limits the maximum accelerating gradient. Various surface treatment recipes using heat treatment and/or impurity diffusion have been developed which demonstrate enhanced performance of SRF cavities. Complete understanding of the underlying mechanism of this enhancement, however, requires a controlled study of the near surface. Depth-resolved measurements of the magnetic field screening below the surface are made possible with this new spectrometer, which combines local magnetic field measurements via spin-polarized radioactive ion beam produced at TRIUMF, and the spectrometer which allows high-parallel field and implantation depth-control of the ions. The magnetic field configuration parallel to the sample surface but transverse to the beam momentum deflects the beam vertically and requires compensation via electrostatic steering. The details of design, assembly, installation, and operations of the beamline and the spectrometer are all presented in this thesis. Depth-resolved measurements on two Nb samples with different surface treatments relevant to SRF cavities have been performed on the new spectrometer up to 200 mT. The results demonstrate the sensitivity of the 𝛃-NMR technique in characterizing the magnetic field screening and provide a working method for future studies. Outlook on future experiments on different SRF materials, as well as potential applications of the new spectrometer for other materials are proposed.