Fundamental Research in SRF at TRIUMF

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Studies to optimize and understand rf performance have been focused on elliptical 1.3GHz cavities for electron acceleration. A new wave of hadron SRF linear accelerators are being developed that would operate with continuous wave (cw) rf power. The cavities for hadron accelerators are non-elliptical structures utilizing the TEM accelerating mode and must accelerate a wide range of particle velocities from 5% to ~80% the speed of light and with rf frequencies ranging from 100MHz to 700MHz typically. ******Our work has convinced us that an understanding of the performance of new processes and new materials requires the ability to study both the microscopic behaviour of materials as well as the performance of full resonator structures. The PI on this proposal has used a previous Discovery grant and RTI funds to support students and equipment to install an rf induction oven, to source two coaxial cavities for rf cryogenic testing at multiple frequencies and to explore the performance of Nb and new materials with muSR (T. Junginger et al. PRAB 2018 21, 032002). In addition RTI funds have been used to purchase equipment for a new betaNMR beamline to further study SRF materials. All the equipment is geared to support student based research programs. ******The funds requested here will allow us to continue to explore materials at the microscopic level utilizing the expertise and equipment at TRIUMF and the University of British Columbia and materials sourced both internally and through external collaborators. In particular we will continue muSR measurements for testing in the bulk and complete the new spectrometer to the -NMR facility to allow testing field suppression at the surface. The facility would allow measurements of the magnetic field penetration in the sample near the limits of the Meissner state as a function of depth through the London layer. The beta-NMR depth profile diagnostic would offer a test infrastructure unique in the world for providing important answers to the effectiveness of layered structures and open new opportunities in SRF research.******Our program of full resonators study will focus mainly on optimizing the performance of non-elliptical coaxial cavities (TEM). The cavities are sized to allow bulk heat treatments including doping in the rf induction oven. During the course of this study we propose to outfit the coaxial resonators with an H-map system and T-map system and the cryostat with multi-axis Helmholtz coils to study flux expulsion in the coaxial geometry. The rf induction oven would also allow development of Nb3Sn coatings on samples then single cell elliptical and TEM mode cavities. The latter would enable testing the effectiveness of Nb3Sn as a function of rf frequency and rf field. ******The funds are requested to enable discovery science. During the quest students and young professionals will be trained while pursuing ground breaking questions. ********