  The superconducting RF linac for LCLS-II calls for 1.3 GHz 9-cell cavities
with an average intrinsic quality factor Q0 of 2.7x10^10 at 2 K and 16 MV/m
accelerating gradient. Two niobium 9-cell cavities, prepared with
nitrogen-doping at Fermilab, were assembled into the Cornell Horizontal Test
Cryomodule (HTC) to test cavity performance in a cryomodule that is very
similar to a full LCLS-II cryomodule. The cavities met LCLS-II specifications
with an average quench field of 17 MV/m and an average Q0 of 3x10^10. The
sensitivity of the cavities' residual resistance to ambient magnetic field was
determined to be 0.5 nOhm/mG during fast cool down. In two cool downs, a heater
attached to one of the cavity beam tubes was used to induce large horizontal
temperature gradients. Here we report on the results of these first tests of
nitrogen-doped cavities in cryomodule, which provide critical information for
the LCLS-II project.
