Tuner overview Concepts and examples Focus: Fast piezo

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


3

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


4

Pneumatic Tuners


5

• 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





< 1 Hz, compensation of Helium pressure fluctuations


6

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


7

“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)


8

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





< 1 Hz, compensation of Helium pressure fluctuations


9

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


10

Brian Rusnak et al

Fast electrical tuning - VCX tuner at Argonne


11

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


Tuning critical because of desire to increase external Q

� Best solution so far: Cold motor tuner with piezo

12

Coaxial ball screw tuner and slide jack tuner (KEK)


13

Renascence tuner (JLAB)


14

Tuner Planned for MSU Re-accelerator

Niobium push-pull tuning plate with convolutions and cuts


15

� 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


16

Soreq

Fast tuners

Saclay I tuner

spindle

piezo

lever system


17

Modified piezo holder frame:Higher wall thickness

flexure tank

Fast tuners – Saclay II tuner

piezo

eccentric spindle


18

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


19

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 step response, meas. by Tom Powers


20

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

)


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


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=

21

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


22

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


23

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)


24

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


> operating voltage � bipolar operation possible� double stroke

coercitive voltage,stroke = 0polarisation = 0

nascent curvevoltage = 0remanent polarisationremaining stroke

butterfly cyclenegative polarisation,positive stroke

25

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


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


27

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:


28

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


dynamic piezo response

29

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


no sparks

V/

p*d/(pd)min

30

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


31

• 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,


32

B. Rusnak

… and many others I have „borrowed“ transparencies from

SRF 2009 Conference

Invitation

SRF 2009 conferenceheld at Helmholtz-ZentrumBerlin (formerly BESSY)


33

Sept 20th – 25th

srf2009.helmholtz-berlin.de

293 K

Hysteresis effects on detuning compensation


4 K

34

New/prototype Fast Tuners

26 cm

Magnetostrictive tuner – ANL/Energen

Piezo fast tuner – ANL


35

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


36

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


37

– Piezoelectric, Magnetostrictive: need further investigation– Cavity stiffening: mechanical engineering design and cost challenge


38

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


39

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

39

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


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


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

Documents

Tuner overview Concepts and examples Focus: Fast piezo