1. Spoke Resonators at Fermilab
TTC 2011, Milan
L. Ristori
Serena Barbanotti, Evgueni Borissov, Ivan Gonin, Timergali Khabiboulline, Robyn Madrak, Frank McConologue, Tom Nicol, Joe Ozelis, Ronak Patel, Youriy Pischalnikov, Warren Schappert, Robert Wagner, Robert Webber, et al.

2. 325 MHz SSR1 1st prototype Zanon, Italy 2nd prototype Roark, USA
Quantity
Original Values  CW machine
Beampipe, shell ID
30 mm, 492 mm
Epeak/Eacc
2.56
Bpeak/Eacc
3.87 mT/(MV/m)
G, R/Q0 , βg
84 , 242 , 0.21
RF structure
1 ms, 9 mA  CW, 1 mA
Loaded BW
388 Hz  43 Hz
He temp, pressure
4.4 K, 900 torr  2.0 K, 20 torr
He press variation
12.9 torr   .25 torr
Accel. Grad., Eacc
10 MV/m  12 MV/m
Q0 at Eacc
> 0.5x109  >1x1010?
LFD co. (jacketed)
3.8 Hz/(MV/m)2  Non-issue
df/dp (jacketed)
-210 Hz/torr  25 Hz/torr
1st prototype
Zanon, Italy
2nd prototype
Roark, USA
FNAL & ANL:
Eacc = Tot acc voltage /Leff 
Leff = Liris = (2/3) = 135 mm
If using:
 Leff *=  = 202.5 mm
Eacc* = 0.67 Eacc
L. Ristori - TTC 2011, Milan

3. RF design of SSR1
The dimensions were varied in MWS to optimize the RF design.
Surface electric (left) and magnetic (right) fields in SSR1.
The field strength increases as the color changes from green to yellow to red.
L. Ristori - TTC 2011, Milan

4. SSR1 Fabrication (Niowave & Roark, USA)
Beam Pipe port
SST Cu Nb
10 resonators currently in production
Spoke with collars
Power Coupler port
L. Ristori - TTC 2011, Milan

5. SSR1 trimming & tuning F trims weld tune 324.8 Goal before processing
50.4
324.8
gaps F
trims
tune
weld
Goal before processing
Chemistry +100 kHz
Cool down +500 kHz
Tune – 150 kHz
Preload – 150 kHz
L. Ristori - TTC 2011, Milan

6. Chemistry and HPR of unjacketed cavities at ANL G150
BCP: two 80 minute sessions
Between sessions, flip top to bottom and replace acid.
Remove 120 microns at 15-16C
Frequency shifts +300 and +70 kHz
HPR: 6 ultra-pure water jets, two each at +40, 90, and -40
2 hrs water time with cavity in 6 different orientations.
L. Ristori - TTC 2011, Milan

7. CW tests bare cavities Cavity 1 – 4th test Cavity 2 – 1st test
During cool down, a 7 hr hold at 100 K produced a large Q0 drop, confirming Q disease.
Subsequently baked SSR1-01 at 600 C for 10 hours at Jlab.
Cavity 2 – 1st test
Effects of Q disease should not appear on first cooldown.
X-rays increase at MP barriers, then disappear after punch through.
L. Ristori - TTC 2011, Milan

8. Jacketing of SSR1-01 and preparation for CW and Pulsed tests in cryostat
10 hr, 600  C vacuum bake for hydrogen degassing at Jlab
Adjust cavity tune at room temperature: fixture to inelastically stretch or compress at beam pipes (capable of  250 kHz).
Weld on the helium vessel: argon purge and temperature and frequency monitoring.
Degreasing, flash BCP (20 min at 13 C) and HPR.
L. Ristori - TTC 2011, Milan

9. Prototype tuner
Two piezo actuators “in series” with slow tuner arms (pivot with 5:1 mech. advantage).
Stepping motor with harmonic drive,1:100 ratio (0.9 Hz/step).
Present tests with a tuner on each end.
Low profile along beam required due to close proximity to solenoid.
dF/dL ~ 540 Hz/um
Max stroke 3 mm
L. Ristori - TTC 2011, Milan

10. Commissioning 325 MHz Spoke Cavity Test Facility(SCTF)
Cooling to 4.5 K. (2 K upgrade is planned).
Primary (secondary) pressure relief of 10 (5) psig. Operation near 5 psig.
200 W solid state supply for CW.
2MW Klystron for pulsed tests (used only 50kW).
Digital LLRF with GUI interface screens .
Locks to cavity frequency for CW operation.
Room temp B shield just inside cryostat wall.
80 K thermal shield. Robyn (runs the place).
Jacketed cavity with tuner. Test magnets.
X-ray detectors along beam line:
Diodes ~10 cm from beampipe flanges
Foxes and Chipmunks ~50 cm outside cryostat.
CW: Drive antenna with Qext = 1.5 x 108
L. Ristori - TTC 2011, Milan

11. Q0 .vs. Eacc scan in first cooldown and Q disease test
Scan in first cooldown compares well with first cooldown of bare SSR1-02 in VTS at 4.4 K.
Maximum Eacc of 27 MV/m is a bit higher.
Within 5% measurement uncertainty, scan was unchanged after a second 3 hour cooldown.
Third cooldown of 11 hours through sensitive region (150 K to 70 K): Much milder case of Q disease than before degassing: At 10 MV/m, Q0 decrease of 20% versus 87% for 7 hour hold at 100 K in last VTS test of bare SSR1-01.
However, 20% decrease at ~4.5 K is about a factor of three decrease at 2 K
L. Ristori - TTC 2011, Milan

12. SSR1 Pulsed Tests at SCTF
These are the first cold tests of the SSR1 with a Power Coupler suitable for accelerator operations.
Cold section with antenna was installed onto cavity port at the MP9 clean room.
Warm section attached through the cryomodule port at the SCTF cave.
The warm section has its own vacuum pump.
36.5 MV/m with a 1.5 ms flat top without quenching.
measured how high one could run as a function of flat top length. It looks like it may level out at about 36 MV/m for CW operation, but this is obviously a large extrapolation.
peak surface B field at Eacc = 36 MV/m is 139 mT (from Ivan's simulation).
L. Ristori - TTC 2011, Milan

13. Tuner tests on jacketed SSR1-01
Microphonics (He pressure fluctuation)
compensation
dF/dP
Pressure, torr
SSR1 Static Lorentz Force Detuning
Coefficient
LF detuning coefficient KLF  (DF=-KLF*Eac2);
KLF[Hz/(MV/m)2] = -1,5
(Predicted -3.8)
DF,Hz
L. Ristori - TTC 2011, Milan

14. SSR1 RF Pulse Mode Operation Lorentz Force Detuning Compensation
Fill=1ms
Flat-Top=1ms
LFD during Flat-Top
Eacc Piezo OFF Piezo On (ApiezoV)
20MV/m 450Hz Hz V(18%)
34MV/m Hz Hz V(40%)
Piezo On
Detuning, Hz
20MV/m
2000Hz
Piezo OFF
DF=-kEacc2
LFD during 1ms Flat-Top
Time
27-34MV/m
K~1,2Hz/(MV/m)2
Detuning, Hz
Piezo On
2000Hz
Piezo OFF
L. Ristori - TTC 2011, Milan

15. Round end walls proposed to avoid “donut rib”
SSR0
SST/Nb braze joints
SSR0 parameters
Aperture
30 mm
F(MHz)
325
βoptimal
0.115
Dcavity,mm
406.84
R/Q, Ω
109.2
G, Ω 51
Emax/Eacc
5.66
Hmax/Eacc
(mT/MV/m)
6.83
Deff(2*βoptλ/2),mm
106
Bolted Nb/SST connections
SST He vessel
E fields
B fields
Round end walls proposed to avoid “donut rib”
One bellow
L. Ristori - TTC 2011, Milan

16. Df/dP, free and locked at beam pipe
dF/dP ~ 14 Hz/torr
Locked
dF/dP ~ Hz/torr
Total deformation: between 0 and 55 µm
BP: below 10 µm
The actual df/dp of cavity + tuner will fall in this range with average of -6 Hz/torr
L. Ristori - TTC 2011, Milan

17. Range of Piezos 100 N on ½ piezo surface (diameter 10 mm)
Max deformation 23 µm
Max stresses 24 MPa (very localized)
Frequency shift ~ 1 kHz for 4 piezo
Frequency shift ~ 250 Hz for 200 N applied by 1 piezo
L. Ristori - TTC 2011, Milan