LCLS II SRF Cavity Tuner (developed by FNAL) DESIGN OPTIMIZATION Mechanical size limitations must fit on the “short-short” cavity (DESY tuner can fit only on “short-long” ). Location of the piezo. Piezo stroke translate directly to the cavity (At DESY design only ½ of piezo stroke going to cavity). Piezo preloaded inside encapsulation. Robust/Low cost tuner frame design. Features that must prevent loosening of the tuner part during 20 years operation (20 thermo-cycles). Design elements that allow to replace active elements of tuner without dis-assembly tuner. NEW ACTIVE COMPONENTS: Electromechanical actuator (stepper/gear/spindle) designed by Phytron per FNAL specs (LVA 52-LCLS II-UHVC-X1) Piezo tuner- encapsulated piezo-stack designed by PI per FNAL specs (PI-885.51) Y. Pischalnikov et al., “Design and Test of Compact Tuner for Narrow Bandwidth SRF Cavities.” In Proc. IPAC2015, Richmond, VA, USA. Y. Pischalnikov et al., “LCLS II Tuner Assembly for the Prototype Cryomodule at FNAL.” In Proc. NAPAC2016, Chicago, IL, USA.

LCLS II SRF Cavity Tuner TUNER PARAMETERS OPTIMIZATION Slow tuner range >600kHz Small hysteresis (45Hz) and backlash 30(steps) for slow tuner Slow tuner sensitivity - 1.3Hz/step

LCLS II SRF Cavity Tuner (FNAL) (3) TUNER PARAMETERS OPTIMIZATION Fast (piezo) tuner range is ~3kHz (at Vnominal=120V) Measured piezo resolution ~0.15Hz (limited by noise in HTS) Lowest mechanical resonances of the tuner/cavity system is 170Hz with major resonance at 235Hz Piezo tuner range will not changed with cavity tuned up to 600kHz

Y. Pischalnikov et al., “Reliability of the LCLS II in SRF Cavity Tuner.” In Proc. SRF2015, Whistler, BC, Canada. Reliability of Electromechanical and Piezo actuators Summary of ALT (accelerated lifetime tests) and Rad-hardness study. Cold/ insulated vacuum test (ALT) of Piezo Actuators at FNAL facilities for equivalent 30 years of operation. Cold/ insulated vacuum test (ALT) of Phytron Actuator at FNAL&JLAB facilities for equivalent 100 years of operation at accelerator – NO FAILURE. Several Piezo successfully tested (ALT) for 20 years of LCLS II operation. Warming up piezo for LCLS II operation less than DT=1K. But for pulse operation like XFEL (or PIP II) piezo will warm up to DT=20K-40K that can decrease life time of piezo drastically Radiation Hardness tests of the Electromechanical Actuator (up to 5*108 Rad) Radiation Hardness tests (up to 5*108 Rad) There was no any degradation in the electromechanical actuator components: Windings of the stepper motor Limit switches Traveling nut PIEZO STROKE decreased only on ~10% from nominal value.

Resonance Control: Tuner Development: Future plans in Resonance Control and Tuner development in the frame of PIP II project at the same time relevant for ILC Resonance Control: continue to improve FNAL’s Adaptive Feed Forward LFD compensation algorithm (successfully deployed during S1Global program) Tuner Development: continue collaboration with Phytron in reducing cost of electromechanical actuators without compromising parameters and reliability of actuators continue collaboration with PI (Physik Intrumente) in developing piezo- capsules for SRF cavities tuners. Major objectives- to build large stroke, large blocking forces capsulated preloaded piezo that can operate without overheating with large operational amplitude and frequency inside cold insulated vacuum enviroment