02 oct 2013

1. Design and operation of a piezo-based cold tuning system Unité mixte de recherche CNRS-IN2P3 Université Paris-Sud91406 Orsay cedex Tél. : +33 1 69 15 73 40 Fax : +33 1 69 15 64 70 http://ipnweb.in2p3.fr 02 oct 2013

2. Outline • Introduction on cavity tuning Why a tuner ? How to tune ? • Case of a spoke deformation tuner Slow tuner principle Fast tuner principle • Operation Setup diagram Optimized adaptive control system Hardware

3. ! Why a tuner ? ? f0 G(dB) Properties from SC cavities : 1/ Narrow bandwidth due to very high quality factor 0 f(Hz) 2/ Resonant frequency (f0) is dependent and very sensitive to the shape of the cavity body  Highly vulnerable to mechanical perturbations such as LHe bath pressure variations, Lorentz forces, thermal shrinks, vibrations (microphonics), etc.

4. How to tune ? Mostly, two ways: 1/ By moving/inserting a SC volume inside the cavity : The plunger tuner 2/ By stretching the cavity : The deformation tuner Spiral2 B-type cryomodule tuner for 88 MHz QWR Blade tuner on the MAX 700 MHz elliptical cavity

5. Case of A spoke deformation tuner Simple Spoke cavity from Orsay, f0= 352 MHz

6. Case of A spoke deformation tuner • Spoke Cavity parameters : • Resonance : 352 MHz • Sensitivity : 700 kHz/mm • Bandwidth : ~250 Hz • Stiffness : 4 kN/mm • CTS requirements : • Fine resolution : < 1/20 of ΔBP • Large tuning range : ~1 mm • High stiffness : several times the cavity stiffness • Hostile environment : • Vacuum : ~10-6mbar • Cold temperature : down to 2K

7. Slow tuner principle Cavity beam pipe flange as support A ball screw system driven by a stepper motor acts on a double lever arm mechanism to provide a significantly reduced displacement of the cavity flange along the beam axis. Lever armD/d=8 Pushing action through 4 rods d D Stepper motor • Design recommendations : • Avoid magnetic materials near the cavity body. Use AISI 316 L stainless steel is a good solution. • Mechanical tuner must properly provide a submicronic motion : preload as much as possible to prevent backlash, take benefit from the cavity as a big spring • Make nice and robust mechanics, avoid friction, avoid hyperstatism as possible. Ball screw

8. Fast tuner principle • Mostly used : Piezo actuators • Apply an electric field, it will expand. • Small stroke (few µm) but very fast action (response time < 1ms) • The things to now : • Stroke is strongly reduced at low temperatures • Brittle : handle with care and if it is possible, make an encapsulation • Avoid absolutely : Torsion, shear and bending forces • Must be properly preloaded (dynamic operation) dV ++++++++ dx - - - - - - - - Piezo actuators (x2) Piezo actuators location : easy access, externally preloaded (thanks to the banana frame) 6.8 µm 6.8 µm 10 µm Static analysis showing additional action provided by the piezos to the cavity (black profile is the initial position)

9. Setup diagram (fast tuner only) Since we operate the cavity resonator inside its bandwidth, we can assume that the phase shift value between forward and transmit RF signal is proportional to the frequency detuning. (phase detector is not represented on the diagram but exist) So, the idea is to regulate this phase value to a defined setpointϕcons Fast tuner controller Loop ϕ Fast Tuner Piezoelectric actuators Fast tuner controller ϕcons - + • Perturbations: • Lorentz Force Detuning (LFD) • Microphonics • LHE bath pressure fluctuations + + Mechanical action DLLRF Loop Cavity Cavity PA DLLRF VcIcons, VcQcons + - VcI, VcQ

10. Room temperature tests

11. OPTIMIZED ADAPTIVE control SYSTEM SP PV ADEX CONTROLLER NOTCH FD NOTCH FD NOTCH FD OUT PERT

12. OPTIMIZED ADAPTIVE control SYSTEM Frequency shift of a 352 Hz cavity at roomtemperature when excited by a square wave: Frequency shift of a 352 Hz cavity at roomtemperature when excited by a square wave filtered with Notch frequency dampers:

13. OPTIMIZED ADAPTIVE control SYSTEM SP PV ADEX CONTROLLER NOTCH FD NOTCH FD NOTCH FD PERT OUT - PASSBAND FILTER CHEBYSHEV FILTER 1 SP-PV CHEBYSHEV FILTER 2 + CHEBYSHEV FILTER 3

14. OPTIMIZED ADAPTIVE control SYSTEM CHEBYSHEV FILTER 1 PROCESS SP PASSBAND FILTER + G - PV

15. OPTIMIZED ADAPTIVE control SYSTEM Final Strategy: SP ADEX CONTROLLER PV NOTCH FD NOTCH FD NOTCH FD NOTCH FD NOTCH FD NOTCH FD OUT PERT - CHEBYSHEV FILTER 1 SP-PV CHEBYSHEV FILTER 2 + CHEBYSHEV FILTER 3

16. Hardware CTS Controller Theory of operation :1- An ADC & DAC control board acquires the phase error signal of the cavity 2- Information is sent from a dsPIC to the DE0 board for digital filtering and returns the result to the main controller3- Main controller (Delfino) receives and processes the digital filtered signal and returns the output signal to the DACs of the Control board via the DE0 board. Main controller ADEX adaptive-predictive algorithm TI Delfino DSP DE0 board Digital filters Quick diagnostics Microchip 16bits DSP Cyclone 3 FPGA Serial interface to host computer 16 bits Parallel interface ADC & DAC Control board Analog I/O distribution Data acquisition & supervision Phase error signal Output analog signal to high voltage amplifier

17. Thanks for your attention Pleasefeel free to askany questions.

18. Small displacement during a test @4K Motor steps Equivalent to 15 nm Equivalent to 0.43 µm Frequency shift 300 Hz