Tests cryomodules B @ lIPN
Unit mixte de recherche CNRS-IN2P3Universit Paris-Sud
91406 Orsay cedexTl. : +33 1 69 15 73 40Fax : +33 1 69 15 64
70http://ipnweb.in2p3.fr
02 oct 2013Design and operation of a piezo-based cold tuning
system
NIntroduction on cavity tuningWhy a tuner ?How to tune ?
Case of a spoke deformation tunerSlow tuner principleFast tuner
principle
OperationSetup diagramOptimized adaptive control
systemHardwareOutlineNWhy a tuner ??
!f(Hz)G(dB)f00Properties 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 (f0) is dependent and
very sensitive to the shape of the cavity bodyNHow to tune ?Mostly,
two ways:1/ By moving/inserting a SC volume inside the cavity : The
plunger tuner2/ By stretching the cavity : The deformation
tuner
Spiral2 B-type cryomodule tuner for 88 MHz QWR
Blade tuner on the MAX 700 MHz elliptical cavityN
Case of A spoke deformation tuner
Simple Spoke cavity from Orsay, f0 = 352 MHzNCase of A spoke
deformation tuner
Spoke Cavity parameters :Resonance : 352 MHzSensitivity : 700
kHz/mm Bandwidth : ~250 HzStiffness : 4 kN/mm
CTS requirements :Fine resolution : < 1/20 of BPLarge tuning
range : ~1 mmHigh stiffness : several times the cavity
stiffness
Hostile environment : Vacuum : ~10-6 mbar Cold temperature :
down to 2KNSlow tuner principle
Cavity beam pipe flange as supportPushing action through 4
rodsBall screwLever armD/d=8Design 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. dDStepper motorA 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.NFast tuner principle
10 m6.8 m6.8 mStatic analysis showing additional action provided
by the piezos to the cavity (black profile is the initial
position)Mostly used : Piezo actuatorsApply an electric field, it
will expand.
Small stroke (few m) 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)
Piezo actuators (x2)++++++++- - - - - - - -dxdVN8Setup diagram
(fast tuner only)DLLRF LoopFast tuner controller Loop
PADLLRFCavityCavityVcIcons , VcQconsVcI, VcQFast tuner
controllercons+-Fast TunerPiezoelectric
actuators++-+Perturbations:Lorentz Force Detuning
(LFD)MicrophonicsLHE bath pressure fluctuationsMechanical
actionSince 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 cons NRoom temperature tests
NOPTIMIZED ADAPTIVE control SYSTEMADEX
CONTROLLERNOTCHFDNOTCHFDPVOUTPERT
NOTCHFDSPNOPTIMIZED ADAPTIVE control SYSTEM
Frequency shift of a 352 Hz cavityat room temperature when
excited by a square wave:Frequency shift of a 352 Hz cavityat room
temperature when excited by a square wave filtered with Notch
frequency dampers:NADEX CONTROLLERNOTCHFDNOTCHFDNOTCHFD-PVCHEBYSHEV
FILTER 1CHEBYSHEV FILTER 2CHEBYSHEV FILTER 3+SP-PVOUTPERTPASSBAND
FILTERSPOPTIMIZED ADAPTIVE control SYSTEMNCHEBYSHEV FILTER
1PASSBAND FILTERPROCESSGSPPV+-
OPTIMIZED ADAPTIVE control SYSTEMNFinal
Strategy:NOTCHFDNOTCHFDNOTCHFDADEX
CONTROLLERNOTCHFDNOTCHFDNOTCHFD-PVCHEBYSHEV FILTER 1CHEBYSHEV
FILTER 2CHEBYSHEV FILTER 3+SP-PVOUTPERTSPOPTIMIZED ADAPTIVE control
SYSTEMNHardware
Output analog signal to high voltage amplifierSerial interface
to host computer16 bits Parallel interfaceADC & DAC Control
board Analog I/O distribution Data acquisition & supervisionCTS
ControllerCyclone 3 FPGATI Delfino DSPDE0 board Digital filters
Quick diagnosticsMain controller ADEX adaptive-predictive
algorithmMicrochip 16bits DSPPhase error signalTheory of operation
: 1- An ADC & DAC control board acquires the phase error signal
of the cavity2- 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.NThanks for your
attentionPlease feel free to ask any questions.NSmall displacement
during a test @4K
Equivalent to 0.43 mEquivalent to 15 nm300 HzMotor
stepsFrequency shiftN
