Innovative Tuner Designs for Low-ββββ SRF Cavities
Zachary A. Conway
Argonne National Laboratory
Physics Division-Linac Development Group
Outline
2
� Why use a tuner?
� Cavity mechanical properties
� Low-β cavity tuner examples
Tuner Requirements
3
CW Pulsed
Fast Tuning
Slow Tuning � Center Cavity Frequency
� Microphonics
� He Pressure
Fluctuations
� Resonant Vibrations
� Over Couple –
Additional RF Power $$$
Operating Mode
� Lorentz Detuning
� Over Couple –
Additional RF Power $$$
� Center Cavity Frequency
Why use a tuner?
� Accelerator cavities must be operated with a stable phase and amplitude
� High beam loading – Reduced dependence on RF frequency errors
4
Mechanical Considerations
� Design to minimize microphonics (can be extremely effective if
considered early)
– Decoupled the RF accelerating mode from common mechanical vibrations
• cw operation - helium pressure fluctuations (M. Kelly, THIOB04, QWR)
• pulsed operation - Lorentz detuning (W. Schappert, FRIOA01)
– Do as much as you can then use a tuner and overcouple to control RF field
� For example
– cw operation – balance contributions to ∆f
– pulsed operation - fabricate with a high rigidity
5
xdxExHfV
32
00
2
00 )()(∫∆
−∝∆ rrrr
εµ
Slater Perturbation Theorem
Cavity Mechanical Design
6
ββββ = 0.5 345 MHz Triple-Spoke Cavity
7
measured ∆∆∆∆f/∆∆∆∆P = -12.4 Hz/torr∆∆∆∆f/∆∆∆∆P = -6.3 Hz/torr
∆∆∆∆f/∆∆∆∆P = -2.5 Hz/torr∆∆∆∆f/∆∆∆∆P = -0.5 Hz/torr
Room temperature test results
Z.A. Conway, SRF2005, TUA06T. Schultheiss & J. Rathke, AES, Modeling
1)
4)
2)
3)
ββββ = 0.077 72MHz Quarter-Wave Cavity
8
Z
Displacement (mm) 0 0.25 0.5 1
Δfp-p (Hz) 0.2 15 33 66
Peak-to-Peak Frequency Deviation For A Center Conductor Offset From Electrical Center Along Z.
Frequency Shift Due To Pendulum-Like Oscillations of Center Conductor
X
Possible to eliminate microphonics due to pendulum mode if done correctly. (J.R. Delayen 1987)
Types of Tuners In Use/Development Today
� Mechanical
– Course slow tuners
• Control The Applied Force
• Control The Applied Displacement
– Fine fast tuners
• Piezo electric
• Magnetostrictive
� Electromagnetic: Voltage Controlled Reactance (VCX)
– Limited application range without further R&D
• Stored Energy < 25 J
• Frequency < ~100 MHz
– No plans to use in future accelerators
9
Tuners Which Control The Applied Force
� Tuner compresses cavity by squeezing at the
beam ports
� This design separates the mechanically
compliant course tuner from the rigid fast tuner
� ANL approach has essentially no direct
interaction with the clean assembly10
Tuning BarsWire Rope Bellows
Fast Tuner Aperture
Helium Gas Input
Helium Gas Actuated Slow Tuner Performance
11
Am
plitu
de (d
B, a
rb)
Pha
se S
hift
(Deg
rees
)
Slow Tuner Response
Slow Tuner Transfer Function
The pneumatic tuner is quite fast >2500 Hz/sec
Zinkann et al, PAC’05, WPAT082
Piezoelectric Fast Tuner
Fast Tuner Cross SectionNb Ring and Button Welded To Cavity
17 c
m
Nb Wall Helium JacketWith 6.75” CF Flange
Belleville Washers
G-10 Thermal Breaks
Piezo Actuators
Differential Screw
Nb RingNb Button
12
Fast Tuner On HWR Cavity
Liquid Nitrogen Out
Kelly et al, LINAC2010, THP057
-180
-135
-90
-45
0
45
90
135
180
0 20 40 60 80 100 120 140 160 180 200
Re
spo
nse
Re
lati
ve
Ph
ase
Sh
ift
(De
gre
es)
Vibration Frequency (Hz)
Fast Tuner Performance on HWR
13
0
10
20
30
40
50
60
70
0 20 40 60 80 100 120 140 160 180 200
RF
Fre
qu
en
cy V
ari
ati
on
Am
pli
tud
e (
arb
.)
Vibration Frequency (Hz)
Examples of Low-ββββ Tuners For CW Operation
14
Tuner Examples
15
ISAC-II Cryomodule @ TRIUMF
760
800
840
880
920
5:19:41 PM 5:21:07 PM 5:22:34 PM 5:24:00 PM 5:25:26 PM
Time, h-m-s
Pre
ssu
re, T
orr
-27000
-23000
-19000
-15000
Tu
ner
Po
siti
on
, ste
p
PressureTuner Position
630
800
850
900
Pre
ssur
e (T
orr)
Time (min)
� Lever connected to tuning plate
� Tuner resolution = 0.04Hz/step
(5nm/step)
� Laxdal et al, SRF2011 THIOB06
Bottom View Of Cavity
Tuner Examples
16
352 MHz β = 0.17 Halfwave
EURISOL R&D
at 293 K.110 kHz tuning range68 kHz/mm
For a similar β = 0.31 cavity at 293 K.150 kHz tuning range227 kHz/mm
Facco et al, PRST-AB 9, 110101 (2006)
Plunger Tuners
17
Spiral2IPN-Orsay
� Can in principle be used on nearly
any cavity with a properly placed
port.
� Moveable niobium rod
� Cooled with helium bath
� Large tuning range = 90kHz
High RRR Niobium PlungerOlry, SRF09, THOBAU04
Example of Low-ββββ Tuner For Pulsed Operation
18
FNAL’s Single Spoke Cavity Tuning
� FNAL developed spoke cavities for a pulsed
high-intensity proton accelerator
� The cavities are reinforced, increasing their
rigidity and minimizing Lorentz detuning, I.
Gonin (FNAL)
� G. Apollinari, SRF’05, TUP34
19
325 MHz Single-Spoke
FNAL’s Single Spoke Cavity Tuner
20
TFlat-Top=1ms
Eacc=30MV/m
TFill=1,2ms
Detuning, Hz
Time
Piezo OFF
Piezo ON
Schappert, Pischalnikov, FRIOA01
Summary
� When designing your cavity it pays to couple your
electromagnetic with your mechanical simulations
Majority of frequency detuning effects can be minimized or
even eliminated by design (neglect can lead to an unusable
system)
� Tuner designs should be tailored to applications; many
designs work but vary in cost, complexity and flexibility
21
Thank You
22
� Scott Gerbick, Mark Kedzie, Mike Kelly, Peter Ostroumov,
Sergey Sharamentov Ken Shepard, and Gary Zinkann (ANL)
� Jean Delayen (ODU)
� Alberto Facco (MSU/INFN-LNL)
� Robert Laxdal (TRIUMF)
� Yuriy Pischalnikov and I. Gonin (FNAL)
� John Rathke and Tom Schultheiss (AES)
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