The LCLS-II HE High Q and Gradient R Program
Daniel Gonnella, Sebastian Aderhold, Daniel Bafia, A. Burrill, Mattia Checchin, Mingqi Ge, Anna Grassellino, G. Hays, Matthias Liepe, Martina Martinello, Ari Palczewski, Sam Posen, Tor O. Raubenheimer, Charles Reece, Alexander V. Romanenko, Marc C Ross · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2019
The LCLS-II HE project is a high energy upgrade to the superconducting LCLS-II linac. It consists of adding twenty additional 1.3 GHz cryomodules to the linac, with cavities operating at a gradient of 20.8 MV/m with a Q₀ of 2.7·10¹⁰. Performance of LCLS-II cryomodules has suggested that operations at this high of a gradient will not be achievable with the existing cavity recipe employed. Therefore a research program was developed between SLAC, Fermilab, Thomas Jefferson National Accelerator Facility, and Cornell University in order to improve the cavity processing method of the SRF cavities and reach the HE goals. This program explores the doping regime beyond what was done for LCLS-II and also has looked to further developed nitrogen-infusion. Here we will summarize the results from this R\ program, showing significant improvement on both single-cell and 9-cell cavities compared with the original LCLS-II cavity recipe.