PERFORMANCES OF HIGH PURITY NIOBIUM CAVITIES WITH DIFFERENT GRAIN SIZES

Conference · Mon Aug 21 04:00:00 EDT 2006

OSTI ID:895292

Ciovati, Gianluigi; Kneisel, Peter; Myneni, Ganapati; Chattopadhyay, Swapan

Grain boundaries have for some time been suspected of influencing the performance of RF cavities made from high purity niobium by limiting the temperature dependent BCS surface resistance to a residual resistance because of impurity segregation and by causing field limitations due to flux penetration. We have carried out a comparative study of the RF behavior of 2.2 GHz TM{sub 010} cavities of identical shape, fabricated from single crystal niobium, niobium of grain sizes of the order of several cm{sup 2} and standard poly-crystalline material. All the cavities were treated with buffered chemical polishing (BCP), post-purified at 1250 ?C and ?in-situ? baked at 120 C. This contribution reports about the results of the measurements of the temperature dependence of the surface resistance Rs(T) and the Q0 vs. Eacc behavior at 2 K. From the analysis of the Rs(T) data at low RF fields material parameters such as gap value, mean free path and residual resistance could be extracted. The dependence of the Q-value on RF field was analyzed with respect to the medium field Q-slope, Q-drop at high fields and the quench fields. The best performance resulted in a breakdown field of {approx}165 mT, corresponding to an accelerating gradient of E{sub acc} {approx} 38 MV/m.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA
• Sponsoring Organization: USDOE - Office of Energy Research (ER)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 895292
• Report Number(s): JLAB-ACC-06-588; DOE/ER/40150-4135
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
BREAKDOWN
CAVITIES
CHEMICAL POLISHING
GRAIN BOUNDARIES
GRAIN SIZE
LINEAR ACCELERATORS
MEAN FREE PATH
MONOCRYSTALS
NIOBIUM
PERFORMANCE
Q-VALUE
SEGREGATION
SHAPE
TEMPERATURE DEPENDENCE