Fermilab, Batavia
The local magnetic field will enhance at the edge of pits demonstrated by simulation results. Although cavity optical inspection systems provide a huge amount of information about surface features, the amount of topographic information is somewhat limited. Here, we report the use of two components silicone-based RTV for replicas that show increased details of topographic data associated with the optical cavity images. We show profilometry scans for replicas, which yield interesting details associated with equator welds and weld pits. The replicas provide contour information that can be used to evaluate mechanisms by which pits and other features limit RF performance. We also show that application of the replica followed by rinsing does not adversely affect the cavity performance.
Fermilab, Batavia
Past oxygen diffusion measurements were mostly conducted with commercial grade niobium. RRR measurement of furnace treated niobium samples showed the oxygen diffusion rate in high purity niobium can be much higher than past measurements. Samples were baked in furnace at various temperatures and subsequently etched incrementally before RRR measurement. Compared to the oxygen concentration of reference niobium sample, a new O diffusion constant can be estimated by the RRR method.
Fermilab, Batavia
Series of single cell and 9-cell cavities have been processed at ANL/FNAL facility. Those cavities represented major cavity and niobium material vendors. All cavity defects are characterized by temperature mapping and replica technique. Most of the defects are located in or next to the electron beam weld zone. Majority of the cavities reached high gradient despite of the defects located in high magnetic field region.
ANL, Argonne
Fermilab, Batavia
A system for electropolishing of 1.3 GHz elliptical single- and nine-cell cavities is in operation at the joint ANL/FNAL cavity processing facility located at Argonne. The system is one peice of a larger 200 m2 complete single cavity processing and assembly facility which also includes clean rooms and high-pressure rinsing. Recently, the electropolishing system has been used to process a series of single and nine-cell cavities. For single cell cavities a good set of EP parameters has been demonstrated based on more than a half dozen complete processing and cold test cycles at ANL/FNAL. The lastest six single cell cavities each exceed EACC=35 MV/m and, at this gradient, have Q in the range 6 109 - 1 1010. The first nine cell cavities electropolished at ANL have not yet reached similar fields (~23 MV/m-26 MV/m) and ongoing activities are focussed on demonstrating >30 MV/m in these cavities. Suitable nine cell EP parameters using the ANL/FNAL EP system including acid/water temperatures, flow rates, current, voltage, air flow etc. are all substantially different than for single-cell cavities and are discussed here.