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- K.E. McGee, K. Elliott, A. Ganshyn, W. Hartung, S.H. Kim, P.N. Ostroumov, J.T. Popielarski, L. Popielarski, A. Taylor, T. Xu
FRIB, East Lansing, Michigan, USA
- G.V. Eremeev, F. Furuta, M. Martinello, O.S. Melnychuk, A.V. Netepenko
Fermilab, Batavia, Illinois, USA
- B.M. Guilfoyle, M.P. Kelly, T. Reid
ANL, Lemont, Illinois, USA
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High-Q0 medium-velocity (beta opt = 0.6) 5-cell elliptical cavities for superconducting linacs are critical technology for advancing current and future projects such as the Proton Improvement Plan II linac and the proposed energy upgrade of Michigan State University’s Facility For Rare Isotope Beams linac, FRIB400. Previous work established the validity of the novel geometry of the FRIB400 prototype 644 MHz 5-cell elliptical β = 0.65 cavities for future high Q0 development. In collaboration with FNAL, two leading-edge high-Q0 recipes, N-doping and Mid-T baking, were tested in the 5-cell format. 2/0 N-doping + cold electropolishing was successful at achieving FRIB400 and PIP-II Q0 requirements, achieving an unprecedented 3.8 x 1010 at 17.5 MV/m, satisfying the FRIB400 Q0 requirements by 1.75 times in a low-gauss environment. Mid-T baking exceeded FRIB400 Q0 requirements by 1.4 times, and benefitted from decreased residual resistance compared to the N-doped cavity test. Systematic ultrasonic thickness measurements in single-cell revealed bulk (150 microns) EP with the modified EP tool is consistent across the inner surfaces of the cavity walls.
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