The SRF cavity gradient achieved in the European XFEL Cryomodule XM59.
The orange bars show individual cavity vertical test results reaching ~ 35
MV/m and the blue bars show the cavity string (cryomodule) test results
reaching 31 MV/m, with just limited by the operation limit at the test facility,
and with keeping further performance possibility. Both measurement results
are given as operational gradient as defined for the European XFEL: quality
factor Q0 >1E10 (ten billions) at 23.6 MV/m, and field emission below 1E-2
mGy/min (10 micro-Gray per minute).