Piezo Studies and Temperature Measurements

1. Piezo Studies and Temperature Measurements Ruben Carcagno May 11, 2005

2. Background • Fast tuners (e.g., piezo tuners) are needed to maintain high RF power efficiency in high gradient (e.g., 35 MV/m) SCRF cavities • Key component for cost reduction of ILC and Proton Driver • FNAL piezo tuner studies were done for the 3.9 GHz CKM deflecting cavity at A0. • Experience and results are transferable to 1.3 GHz cavities for the ILC and Proton Driver. R&D in these areas will continue at HPTF. Ruben Carcagno - AAC Review

3. Detuning and RF Power • RF power increase for field control due to detuning: Δf = cavity detuning (Hz) f1/2 = cavity bandwidth ~ 200 Hz for 1.3 GHz TESLA cavities ~ 65 Hz for 3.9 GHz CKM cavities • Detuning highly sensitive to small changes in cavity shape • Example: 13-cell, 3.9 GHz CKM cavity (from FEA) Ruben Carcagno - AAC Review

4. Detuning Sources • Fast, small changes in cavity shape are caused by two primary sources: • Lorentz Forces (electromagnetic): • Important for pulsed operation, high gradients (e.g., 35 MV/m) • Highly repetitive • Main detuning concern for ILC and Proton Driver • Piezo compensation demonstrated at the Tesla Test Facility • Microphonics (vibration sources) • Important for cw operation, narrow bandwidth • Random • Microphonics compensation less advanced than Lorentz • FNAL work at A0 contributed to advances in the state of the art of microphonics detuning compensation Ruben Carcagno - AAC Review

5. Detuning Compensation: Fast Tuners Fast tuners have been proposed for active detuning control by applying a counteracting force to the cavity • PIEZOELECTRIC ACTUATORS • Commercially available from multiple sources • Typically used at room temperature • Work at cryogenic temperatures with reduced stroke. Characterization important • Actuator of choice in other labs for detuning compensation studies • MAGNETOSTRICTIVE ACTUATORS • Being introduced as an alternative to piezoelectric actuators for SCRF fast tuning • Newer technology for this application, single source • Some labs are investigating this option Ruben Carcagno - AAC Review

6. Studies at 1.8 K3-cell 3.9 GHz CKM cavity • Microphonics Spectrum with pumps ON and OFF • Vibration measurements with piezo as a sensor • Piezo-RF detuning transfer function • Manual microphonics detuning piezo compensation • Quench and hot spot location using thermometry Temperature Rings Piezo Actuator P-206-40 from Piezosystem Jena Ruben Carcagno - AAC Review

7. Manual Detuning Compensation • Cavity system support was not optimized to minimize microphonics • Microphonics spectrum shows a strong detuning frequency at ~ 30 Hz • Detuning compensation at 1.8 K was attempted by manually adjusting the piezo frequency, amplitude, and phase • Detuning was reduced by more than a factor of three and maintained for several seconds • The result was reproducible, showing the feasibility of using a piezo actuator to compensate microphonics detuning Ruben Carcagno - AAC Review

8. Studies at Room TemperatureAutomatic Microphonics Detuning Compensation Piezo Automatic compensation with an adaptive feedforward control method demonstrated in a 13-cell CKM cavity at room temperature. For details, see: R. Carcagno, L. Bellantoni, T. Berenc, H. Edwards, D. Orris, A. Rowe, “Microphonics Detuning Compensation in 3.9 GHz Superconducting RF Cavities,” 11th Workshop on RF-Superconductivity SRF 2003. Ruben Carcagno - AAC Review

9. Detuning Compensation Results • Automatic compensation demonstrated for three induced frequencies (15 Hz, 27 Hz, and 45 Hz) • More than 20 dB attenuation • Mechanical Resonances quickly identified by driving piezo with white noise Ruben Carcagno - AAC Review

10. Piezo R&D – Next StepsILC and Proton Driver Support Capture Cavity 2 Tuner • Piezo R&D will continue with the HPTF Capture Cavity 2 test • Integrate piezo with cavity tuner • Start with DESY design • Studies at 2 K for ILC and Proton Driver: • Lorentz detuning compensation • Microphonic detuning compensation • Piezo characterization and reliability under operating conditions • Integrate piezo control with LLRF controls • Evaluate Alternatives (e.g., magnetostrictive actuators) • Increase collaboration efforts with other Labs and institutions (e.g., DESY, ANL, JLab, Saclay, etc) Two Piezos • Challenges • Piezo mechanical integration with tuner (preload, reliability) • Mechanical resonances (complicate control algorithms) • Cost/space reduction for mass production and industrialization (power amplifiers, piezo size) Ruben Carcagno - AAC Review

11. Fast Cavity Thermometry • Traditional Carbon Glass RTDs used in SCRF thermometry (e.g., Cornell system) too large for small 3.9 GHz CKM cavity geometry New system based on smaller CERNOX sensors was developed at FNAL Fast (10 kHz) temperature acquisition rate to study quench evolution Ruben Carcagno - AAC Review

12. Thermometry Results • Quench location clearly identified • Hot spot shifts 90 degrees with cw polarization mode • Increasing RF power resulted in quench at hot spot location Lambda point Ruben Carcagno - AAC Review

13. Conclusions • FNAL has already begun developing expertise in areas of piezo tuning and cavity thermometry • R&D in these areas has resulted in advances in microphonics detuning compensation and the ability to pinpoint quench location in small cavities • The focus of this work is now shifting towards ILC and Proton Driver support • Piezo tuning development work will continue with the HPTF Capture Cavity 2 test • Fast tuning (e.g., piezo) capability is critical for cost reduction efforts in high gradient SCRF machines (high RF power efficiency) Ruben Carcagno - AAC Review