  The off-frequency detune method is being considered for application in the
LCLS-II-HE superconducting linac to produce multi-energy electron beams for
supporting multiple undulator lines simultaneously [1]. Design of the tuner has
been changed to deliver roughly 3 times larger frequency tuning range. Working
requirements for off-frequency operation (OFO) state that cavities be tuned at
least twice a month. This specification requires the in-crease of the tuner
longevity by 20 times compared with LCLS-II demands. Accelerated longevity
tests of the LCLS-II HE dressed cavity with tuner were conducted at FNAL's HTS.
Detail analysis of wearing and impacts on performances of the tuner's piezo and
stepper motor actuators will be presented. Additionally, results of longevity
testing of the dressed cavity bellow, when cooled down to 2 K and compressed by
2.6 mm for roughly 2000 cycles, will be presented.
