Title :
Q disease on 350-MHz spoke cavities
Author :
Tajima, Tsutomu ; Edwards, R.L. ; Liu, J. ; Krawczyk, F.L. ; Schrage, D.L. ; Shapiro, A.H.
Author_Institution :
Los Alamos Nat. Lab., NM, USA
Abstract :
Q disease, i.e., an increase of RF surface resistance due to hydride precipitation, has been investigated with 350-MHz spoke cavities. This phenomenon was studied extensively in the early 1990s with cavities at frequencies >1 GHz. This is possibly due to the fact that the lower-frequency cavities were believed to show insignificant effect. However, early 500-MHz KEK elliptical cavities and JAERI 130-MHz quarter wave resonators have shown significant Q degradation, suggesting that this disease can be a serious problem with lower-frequency cavities as well. Since there were no quantitative data with 350-MHz cavities, we decided to measure our two spoke cavities. Our spoke cavities were made of RRR∼250 niobium and were chemically polished ∼150 microns. A few series of systematic tests have shown that our spoke cavities do not show any Q0 degradation after up to ∼24 hours of holding the cavity at 100 K. However, it starts showing degradation if it is held for a longer time and the additional loss due to the Q disease increases linearly. It was also found that our spoke cavity recovers from Q disease if it is warmed up to 150 K or higher for 12 hours.
Keywords :
Q-factor; accelerator RF systems; accelerator cavities; beam handling techniques; superconducting cavity resonators; surface resistance; 100 K; 12 hour; 130 MHz; 350 MHz; 500 MHz; Q degradation; Q disease; RF surface resistance; elliptical cavities; hydride precipitation; lower-frequency cavities; niobium; quarter wave resonators; spoke cavities; Chemicals; Degradation; Diseases; Hydrogen; Niobium; Radio frequency; Surface resistance; Surface treatment; System testing; Temperature distribution;
Conference_Titel :
Particle Accelerator Conference, 2003. PAC 2003. Proceedings of the
Print_ISBN :
0-7803-7738-9
DOI :
10.1109/PAC.2003.1289700