LCLS-II HE R&D ongoing results Background to recipe development Results - 2 of 12 test Ari Palczewski Monday, April 22, 2019

Background JLab LCLC-II HE R&D recipe 800°C 3N60 EP5/10/? This recipe (2N60 in 2015) showed one cavity quenching above 31MV/m with a reasonable Q0 for the material. This recipe should be tried on multiple cavities with multiple doping to verify statistics or abort, i.e. is this recipe actually good. Goal ~ 3e10 @ 21MV/m with Quench field >30MV/m on good flux expelling material JLab LCLC-II HE R&D plan – 12 tests Heat treat three cavities (3N60) at a time in furnace, and perform a 5 micron EP on each, test perform additional 5 micron EP, test Break point – good or bad or ? If good i.e they all meet the goal, reset all cavities and redo study for statistics If gradient bad but Q0 still good, 5 more micron EP and then evaluate If gradient and Q0 unacceptable, abort plan and reformulate

Background JLab LCLC-II HE R&D cavities Three prequalified single cell cavities need for the study All cavities must have gradient close to 24MV/m with a Q0@16MV/m ~3.5e10 SC-04, SC-07 and SC-08 made by RI for LCLS_II TD material batch qualification selected. All cavities quenched between 23 and 26MV/m. All cavities showed at least 80% flux expulsion @ 5K gradient across the cavity except SC-07 which only shows 70% and does not level out – next slide All cavities received additional 900°C 3Hr heat treatment and then 50 micron EP reset. – ready for the study

Flux expulsion baseline cavities

SC-08 results – Quench @ 36MV/m

SC-08 results – Quench @ 36MV/m cont.

Sc-07 results – quench @ 16.5MV/m Modern SRF cavity assembly and practices