The SLAC National Accelerator Laboratory is currently constructing a major upgrade to its accelerator, the Linac Coherent Light Source II (LCLS-II). Several Department of Energy national laboratories, including the Thomas Jefferson National Accelerator Facility (JLab) and Fermi National Accelerator Laboratory (FNAL), are participating in this project.The 1.3-GHz cryomodules for this project consist of eight cavities produced by two vendors, Research Instruments GmbH in Germany (RI) and Ettore Zanon S.p.a. in Italy (EZ), using niobium cell material from Tokyo Denkai Co., Ltd. (TD) and Ningxia Orient Tantalum Industry Co., Ltd. (OTIC/NX).
The initial production cavities showed multiple deficiencies including manufacturing flaws from one vendor, high rates of field emission from both vendors and Qo reduction from a previously unknown flux trapping/pinning material dependence. Additional new cavities material from Tokyo Denkai (TD) has been purchased; TD showed the best flux expulsion and RF performance at the lowest heat treatment temperature from the original two niobium vendors (OTIC Ningxia being the other). Because there is still not a full understanding of the reason why the TD material performed better than the OTIC material, single-cell cavities from each new niobium heat treatment lot are being made with the standard 900°C annealing w/ 800°C doping recipe ahead of the 9-cell cavities. These single cells must be tested/analyzed prior to the 9 cells' (made from the same batch) heat treatment cycle. We will report on the single cell flux expulsion results and how they correlate to manufacture supplied material properties.