tuner overview concepts and examples focus: fast piezo
TRANSCRIPT
Cavity Tuners
Oliver Kugeler
Outline
ERL workshop 2009, Cornell
Outline
Tuner overview
Concepts and examples
Focus: Fast piezo tuners for ERLs
Advanced piezo tuning
Objectives for tuners
• Tune cavity resonance to operating frequency after cool-down
• De-tune cavity on purpose to bypass operation
• Find resonance after RF-field loss
• Compensate slow frequency drift
• Compensate Lorentz force detuning (in pulsed machines)
• Compensate microphonics (in CW-machines)
• Design issues
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
• Design issues
− long lifetime
− tuner resolution
− compact
− low hysteresis / backlash
− limit range to avoid plastic deformation of the cavity
− limit cross-talk to neighboring cavities
− limit cryo-heatload
− provide serviceability
2
Tuning concepts
Tuner Type Comments
Very slow
Quasi-static, pre tuning only
Niobium plunger Penetration into RF space
Three stub tuner Also coupling changed
Pneumatic bellows Few moving parts
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Slow tuning – niobium plunger
• High RRR 3 cm niobium plunger into the cavity rf
space
• 1100 Hz/mm tuning sensitivity; 90 kHz tuning window
• 11% additional rf loss at 6.5 MV/m; mostly on SS
flange and bellows
used at Spiral-2
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Pneumatic Tuners
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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• used at ATLAS• flexible bellow moved by 0...1atm gHe• tuning range ~ 100 kHz• pro: low parts count
Tuning concepts
Tuner Type Comments
Very slow
Quasi-static, pre tuning only
Niobium plunger Penetration into RF space
Three stub tuner Also coupling changed
Pneumatic bellows Few moving parts
< 1 Hz, compensation of Helium pressure fluctuations
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Slow Warm motor + lever + tuning plate Large size, good serviceability
Cold motor driven lever Small size
ELBE tuner
� Dual spindle lever system� Motor outside the vacuum� Good serviceability
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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“Slow” Tuner at Triumf
External motor drive
Internal
preloaded
precision ball nut
Brushless
servomotor
Double pre-
Twin opposing
angular contact
bearing block
� Precision servo-motor and ball screw on top of
cryomodule
� Actuator extends (through bellows) to a lever
mechanism to the tuning plate
� Relatively fast response time, up to 30 Hz
� Tuner sensitivity 0.04 Hz/step; corresponds to 5nm/step
� Tuner accurately tracks induced helium pressure
fluctuations (lower right)
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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0
Double pre-
loaded linear ball
bearing
Precision 2mm
lead ball screw
Tuner actuator
shaft
Pressure
Tuner Position
630
800
850
900
Pre
ssure
(Torr
)Time (min)
Tuning concepts
Tuner Type Comments
Very slow
Quasi-static, pre tuning only
Niobium plunger Penetration into RF space
Three stub tuner Also coupling changed
Pneumatic bellows Few moving parts
< 1 Hz, compensation of Helium pressure fluctuations
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Slow Warm motor + lever + tuning plate Large size, good serviceability
Cold motor driven lever Small size
Fast
Microphonics compensation, LF compensation
None / overcoupling Simple, high RF power needs
Variable reactance Low cost, limited applicability
Mechanical with piezo Development required
Variable reactance (VCX) tuner at Argonne
• Based on a set of 10 parallel 77 K PIN diodes
• Coupled directly to the cavity fields through an inductive
loop mounted on a cavity coupling port
• Diodes are switched on and off; switching the cavity
between two frequency states in order to adjust cavity phase
• Reliable, inexpensive
• Only developed for f<150 MHz; limited switching power; a
fast mechanical tuner is desired for future ATLAS upgrades
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Brian Rusnak et al
Fast electrical tuning - VCX tuner at Argonne
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Brian Rusnak et al
Demanding requirements for ERL machines
Use high-energy, high-Q0 cavities
High amplitude and phase stability ( ∆A/A = 0.0001, ∆φ=0.02° )
Minimizing of microphonics even more important thanin other linacs due to energy recovery process
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
Tuning critical because of desire to increase external Q
� Best solution so far: Cold motor tuner with piezo
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Coaxial ball screw tuner and slide jack tuner (KEK)
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Renascence tuner (JLAB)
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Tuner Planned for MSU Re-accelerator
Niobium push-pull tuning plate with convolutions and cuts
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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� Based on a warm linear stepper motor plus
piezo electric stack
� Force applied through to a tuning rod to a tuning plate
on the bottom of the cavity
� ~20 kHz tuning range (+/- 25 mm) using stepper motor
300 Hz full range with piezo
with convolutions and cuts
Saraf tuner developed by ACCEL
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Soreq
Fast tuners
Saclay I tuner
spindle
piezo
lever system
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Modified piezo holder frame:Higher wall thickness
flexure tank
Fast tuners – Saclay II tuner
piezo
eccentric spindle
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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flexuretank
Fast tuners - Blade tuner
use for booster/gun where RE gradient is vital
2 piezos on opposite sites
� compensate vertical oscillations
1st DESY prototype (Kaiser, Peters)
Latest version tested at HoBiCaT
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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modified version
(Peters, Pagani)ILC version (Pagani)
Saclay tuners
-6000
-5000
-4000
-3000
-2000
-1000
0
1000
150
200
250
300
350
400
ph
as
e (
°)
am
pli
tud
e (
Hz)
amplitude (Hz)
phase (°)
-3000
-2500
-2000
-1500
-1000
-500
0
500
60
80
100
120
140
160
amplitude (Hz)
phase (°)
Saclay I Saclay II
-20
0
20
40
60
80
100
-0.1 0 0.1 0.2 0.3 0.4 0.5Time (s)
Fre
q S
hift
(Hz)
0
20
40
60
PZ
T D
rive
(V
)
Cavity Frequency Shift (Hz)
Piezo Drive Voltage (V)
80
100
50
60Cavity Frequency Shift (Hz)
Piezo Drive Voltage (V)
Piezo step response, meas. by Tom Powers
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Saclay I Saclay II
Excitation amplitude 22.5 Hz 19 Hz
Maximum cavity response 340 Hz 150 Hz
-9000
-8000
-7000
-6000
0
50
100
0 200 400
am
pli
tud
e (
Hz)
frequency (Hz)
-4500
-4000
-3500
-3000
0
20
40
0 200 400
frequency (Hz)-20
0
20
40
60
80
-0.02 0 0.02 0.04 0.06 0.08 0.1Time (s)
Fre
q S
hift
(Hz)
0
10
20
30
40
50
PZ
T D
rive
(V
)
Piezo Drive Voltage (V)
10
15
20
am
plitu
de (H
z)
-60
-40
-20
0
ph
ase (°)
10
15
20
am
plitu
de
(H
z)
-100
-50
0
50
ph
as
e (
°)
amplitude (Hz)
phase (°)
Group delay:
360µs 150µs
ϕd
Transfer functions
Saclay I Saclay IIDouble resonance
BW BW
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
0
5
10 20 30 40 50 60 70 80 90 100
frequency (Hz)
-100
-80amplitude (Hz)
phase (°)0
5
10 20 30 40 50 60 70 80 90 100
frequency (Hz)
-200
-150
ω
ϕτ
d
d=
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Saclay I Saclay II
Group delay at low frequencies 361 µs (290 µs for starting position) 150 µs
Lowest resonance at 40 Hz single double structure
cavity is blind to higher frequency microphonics
���� try to increase lowest resonance
���� make tuner stiffer, increase wall thickness
Stiffening the cavity
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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difference in transfer function
after correction
almost no difference
Fast piezo tuner comparison
Design Saclay I Saclay II Blade Tuner
Motor tuning range 750 kHz 500 kHz 550 kHz
Motor hysteresis satisfying backlash problems at lowamplitudes
Piezo tuning range 840 Hz 1420 Hz 1400 Hz
Group delay 360 µs 150 µs 650 µs
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Group delay 360 µs 150 µs 650 µs
Stiffness lower higher Lowest
Lowest resonance 40 Hz 40 Hz 35 Hz
Microphonics compensation with Saclay I tuner
ΣΣΣΣFFT
w/o feedback
with feedback
with feedbackand feed-forward
compensation
time (s)
detu
nin
g(H
z)
frequency (Hz))
detu
nin
g(H
z)
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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σσσσf = 2.52 Hzσσσσf = 0.89 Hzσσσσf = 0.36 Hz
time (s)
detuning (Hz))
frequency (Hz))
Microphonics measurementsdone at HoBiCaT
Is this the limit?What is the piezo resolution?
# c
ounts
Piezo hysteresis stroke vs. voltage
Strain2
3
5
293 K
4 K
destructive
voltage limit
stroke
reduction
increased
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
> operating voltage � bipolar operation possible� double stroke
coercitive voltage,stroke = 0polarisation = 0
nascent curvevoltage = 0remanent polarisationremaining stroke
butterfly cyclenegative polarisation,positive stroke
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Voltage1
3
4
coercitive voltage
remanent
polarisation
reduction
= 1 : 9
1500
2000
2500
3000fr
equency c
hange (
Hz)
1500
2000
2500
3000fr
equency c
hange (
Hz)
Piezo hysteresis for blade tuner
piezo 1 & 2
both piezos
maximum
frequency
remanencemaximum
coercitive
voltage
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
0
500
1000
-20 0 20 40 60 80 100 120 140 160
frequency c
hange (
Hz)
piezo voltage (V)
0
500
1000
-20 0 20 40 60 80 100 120 140 160
frequency c
hange (
Hz)
piezo voltage (V)
26
1µm cavity strain
voltage
used semi-bipolar
voltage supply
Piezo relaxation
800
1000
1200
1400
1600
1800fr
equency
change
( H
z)
piezo - first cycle
piezo - second cycle
second ramp
stable behavior
viscoelasticdiscrepancy
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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0
200
400
600
800
-20 0 20 40 60 80 100 120 140
frequency
piezo voltage (V)
nascent curvepiezorelaxation
Hysteresis modeling
Assume that piezo behavior is fully deterministic
∫∞−
+=
t
t
s sduVYtuµtX )()()()(2
Voltage
Bouc –Wen model:
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Fast tuning algorithm needs to incorporate
previous history of piezo voltages.
How do we gain access to the history function Y(V(s,t)) ?
Stroke Voltage(Hooke‘s law)
Strain history
Piezo dynamic hysteresis behavior
amplitude resolved transfer function
amplitudefrequency
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
dynamic piezo response
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amplitude resolved transfer function
sparks
V/V
s,m
in
normalized Paschen curve
High voltage vs. low voltage piezos
HV vs. Multilayer piezo: Sparking voltage considerationsPaschen‘s law [F. Paschen, Wied. Ann. 37, 69 (1889)]
))/1ln(
ln(γ
Apd
BpdVs =
Literature:Helium: V , = 156 V
1000V
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
no sparks
V/
p*d/(pd)min
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Helium: Vs,min = 156 V
(pd)min = 4.0 torr/cm= 0.53 mbar/mm
1mm piezolayers: sparks at 0.5 mbar … 40 mbar0.1mm distance: sparks at 0.05mbar … 4 mbar
Can use HV piezos!
0.3 20
Outlook
Combined stepper motor and piezo tuning is the method of choice, but:
Most piezo tuners have been developed for pulsed operation
What could be improved in a CW-only tuner?
• Sacrifice tuning range for stiffness: use shorter piezos
• Shorter piezos also reduce hysteresis effects
• Use high voltage piezos for stiffness
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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• Use high voltage piezos for stiffness
• Use 2 piezos on radially opposing sites in order to access vertical vibrational
modes of the cavity
• Increase cavity wallsize to increase frequency of lowest tuner resonance
• Improve stability of microphonics compensation algorithms
• Incorporate piezo hysteresis into compensation algorithm in order to
effectively increase piezo resolution
• Use bipolar power supplies (and increase mechanical pre-stress on piezo)
• Increase cavity stiffness to increase frequency of lowest resonance
Summary and acknowledgements
Thanks are due to
A. Neumann, A. Bosotti, R. Papparella, M. Luong, G. Devanz
(measurements)
M. Kelly, T. Powers, J. Delayen, S. Simrock, Z. Conway, E. Daly,
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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B. Rusnak
… and many others I have „borrowed“ transparencies from
SRF 2009 Conference
Invitation
SRF 2009 conferenceheld at Helmholtz-ZentrumBerlin (formerly BESSY)
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Sept 20th – 25th
srf2009.helmholtz-berlin.de
293 K
Hysteresis effects on detuning compensation
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
4 K
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New/prototype Fast Tuners
26 cm
Magnetostrictive tuner – ANL/Energen
Piezo fast tuner – ANL
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Combination fast/slow tuner – SARAF/ACCEL
� No fast mechanical tuners of these types in routine operation with low-, mid-beta SRF linacs
KEK Slide Jack Tuner
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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Microphonics compensation
Approaches to Compensate Microphonic Detuning• Microphonic detuning is more a cost and implementation challenge than a technical “show stopper”• It comes down to where the effort and resources are placed:– Overcoupling: costly, wastes RF, but is effective– VCX fast tuning: efficient, needs further development– Piezoelectric, Magnetostrictive: need further investigation
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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– Piezoelectric, Magnetostrictive: need further investigation– Cavity stiffening: mechanical engineering design and cost challenge
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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tuner electrical mechanical purpose
slow
niobium plunger
���� penetrationinto rf space
lever/motor + tuning plate
pre-tuning
compensate He-pressure
fluctuations
< 1 Hz
cold motor driven
lever
pneumatic bellows
Tuning concepts
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
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fast
none / overcoupling
high rf power needs,
use stiffer cavitiesmechanical lever +
piezo
microphonics
compensation
Lorentz force
compensationvariable reactance,
limited applicability
limited range,simplicity
high range
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Feature list from ERL 2005 (by E. Daly)
• Coarse Tuning Mechanism
– Typically cold, must be reliable and maintainable � access ports
– Direct cavity drive reduces stiffness requirements on helium vessel
– Tuner/HV stiffness > 10x cavity
– Flexures exhibit reduced backlash
• Fine Tuning Actuators
– Piezo–operate in compression, warm range 5-10x > cold range, capacitive device, minimize
voltage, consider hysteresis
– MST –must operate cold, consider lead thermal design, inductive element, minimize
current, consider hysteresis
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
current, consider hysteresis
• Transmission Location (maintainability)
– Cold placement requires proper materials, cyclic life testing and access for repair or
replacement, electrical feedthroughs
– Warm placement requires cooldown/tuning compliance, access ports, bellows
• Testing (minimizes risk associated with reliability and availability)
– Perform accelerated life tests on critical components
– Feedback results into design prior to production
– Develop thorough acceptance tests to verify operation
40
1500
2000
2500
3000fr
equency c
hange (
Hz)
1500
2000
2500
3000fr
equency c
hange (
Hz)
Piezo hysteresis for blade tuner
piezo 1 & 2
both piezos
maximum
frequency
remanencemaximum
coercitive
voltage
Oliver Kugeler – Cavity Tuners – ERL09 workshop at Cornell, June 8th - 12th 2009
0
500
1000
-20 0 20 40 60 80 100 120 140 160
frequency c
hange (
Hz)
piezo voltage (V)
0
500
1000
-20 0 20 40 60 80 100 120 140 160
frequency c
hange (
Hz)
piezo voltage (V)
41
1µm cavity strain
voltage
used semibipolar
voltage supply only