1 Unité mixte de recherche CNRS-IN2P3 Université Paris-Sud 91406 Orsay cedex Tél. : +33 1 69 15 73 40 Fax : +33 1 69 15 64 70 http://ipnweb.in2p3.fr 02 oct 2013 Design and operation of a piezo- based cold tuning system
2 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 ? ! f(Hz) G(dB) f0f0 0 Properties from SC cavities : 1/ Narrow bandwidth due to very high quality factor Highly vulnerable to mechanical perturbations such as LHe bath pressure variations, Lorentz forces, thermal shrinks, vibrations (microphonics), etc. 2/ Resonant frequency (f 0 ) is dependent and very sensitive to the shape of the cavity body
4 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
6 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 -6 mbar Cold temperature : down to 2K
7 Cavity beam pipe flange as support Pushing action through 4 rods Ball screw Lever arm D/d=8 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. d D Stepper motor 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.
8 Static analysis showing additional action provided by the piezos to the cavity (black profile is the initial position) 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) Piezo actuators location : easy access, externally preloaded (thanks to the banana frame) ++++++++ - - - - dx dV
9 DLLRF Loop Fast tuner controller Loop PA DLLRF Cavity V cI cons, V cQ cons V cI, V cQ Fast tuner controller ϕ cons + - Fast Tuner Piezoelectric actuators ϕ + + - + Perturbations: -Lorentz Force Detuning (LFD) -Microphonics -LHE bath pressure fluctuations Mechanical action 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 setpoint ϕ cons
12 Frequency shift of a 352 Hz cavity at room temperature when excited by a square wave: Frequency shift of a 352 Hz cavity at room temperature when excited by a square wave filtered with Notch frequency dampers:
16 Output analog signal to high voltage amplifier Serial interface to host computer 16 bits Parallel interface ADC & DAC Control board Analog I/O distribution Data acquisition & supervision CTS Controller Cyclone 3 FPGA TI Delfino DSP DE0 board Digital filters Quick diagnostics Main controller ADEX adaptive- predictive algorithm Microchip 16bits DSP Phase error signal 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 controller 3- 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.