Fermilab, Batavia
Five 3.9 GHz 9 cell cavities have been measured for the DESY FLASH module. These cavities were BCP processed and reached gradients of typically about 25 MV/m with Q drop starting at about 20 MV/m. Recently one cell cavities have been processed with EP and at least one has tested to a gradient of 30 MV/m with Q drop starting at about 25 MV/m. We will compare the results and give an update to the thermal analysis in relation to global thermal breakdown at 3.9 GHz.
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
BNG, Würzburg
Fermi National Accelerator Lab is continuing to improve its infrastructure for research and development on the processing of superconducting radio frequency cavities. A single cell 3.9 GHz electropolishing tool built at Fermilab and operated at an industrial partner was recently commissioned. The EP tool was used to produce a single cell 3.9 GHz cavity that reached an accelerating gradient of 30 MV/m with a quality factor of 5 109. A single cell 1.3 GHz cavity was also electropolished at the same industrial vendor using the vendor’s vertical full-immersion technique. On their first and only attempt the vendor produced a single cell 1.3 GHz cavity that reached 30 MV/m with a quality factor of 1 1010. These results will be detailed along with preliminary tumbling results.