1. C75 Cryomodule Project Outline
G. Ciovati
for the SRF Department
08/03/2017

2. Acknowledgments SRF R&D R. Rimmer, F. Marhauser, J. Guo Engineering
G. Cheng, E. Daly, F. Fors, C. Hovater
SRF Cavity Fab. Group
L. Turlington, B. Clemens, J. Henry, S. Williams
Machine Shop
D. Combs, R. Martin, J. Dail
SRF Cavity Prod. Group
A. Anderson, K. Davis, C. Dreyfuss, J. Follkie, D. Forehand, T. Harris, C. Johnson, R. Overton, T. Sessoms, A. Wildeson
SRF Test and Meas. Group
N. Brock, C. Wilson
SRF CM Assembly Group
J. Fischer, R. Legg, M. McCrea
Accel. Div. Management
A. Freyberger, A. Hutton, A. McEwen, G. Myneni

3. C75: a more efficient way to refurbish CMs
Minimal changes to current C50 module/process
Change cells to increase gradient and Qo
Preliminary Design Review on Jan 21st, 2016 endorsed the project

4. C75 draft specifications
Cavity Parameters
Unit
C75
Energy Gain
MeV 75
Number of cavity cells 5
Cavity active length m
0.4912
R/Q (β = 1) Veff2/(ω*W) Ω
525.4
Eacc
MV/m
19.07 ± 10%, spread
 21 MV/m max.
Maximum beam current μA
460
Beam loading kW
4.31 (4.74 max.)
Design 2.07 K
8e9
Pcav W
20.9 (25.3 max.)
Qext,opt – no microphonics
3.9e7
Peak-to-peak microphonics Hz
± 20
Qext,opt
2.8e7
Design Qext
1.8 – 4.3e7
Required forward RF power 6
(7.6 kW, ~ 1 dB added for klystron power)
~21 W/cavity, ~200 W cryomodule total heat load
<Total HL>C50 ~190 W

5. C75 cavity design
Cell shape is a “low-loss” type, designed for high-current FEL
Distance end-cell-to-FPC optimized for Qext ~2×107
Stiffening rings added to obtain the same stiffness as C50 cavity

6. E.-M. parameters C20/C50 cavity C75 cavity Cavity Parameters Unit
Original CEBAF/
Cornell (OC)
High Current (HC)
Cavity active length m
0.500
0.4912
R/Q*G/cell Ω2
26441
28961
Epk/Eacc
2.83
2.45
Bpk/Eacc
mT/(MV/m)
4.62
4.18
kcc %
3.15
+ 10%
- 13.6%
- 9.4% =
C20/C50 cavity
C75 cavity

7. Cavity material Cells made from Nb discs sliced from an ingot
Technology pioneered in 2004 at JLab through a CRADA with CBMM, Brazil
Medium purity (RRR= ) ingot is a good compromise between lower cost and performance
Many single- and multi-cell cavities built, processed and tested at JLab
quench field
1.5 GHz (OC shaped cavities)
C75 spec.
C75 spec.

8. Ingot Nb technology validation
Eleven 1.3 GHz 9-cell cavities built at RI, Germany. Processed and tested at DESY
7 cavities installed in Cryomodule XM-3 resulted in 45% lower RF heat load than standard fine-grain, high-RRR cavities
Nb from W.C. Heraeus, Germany, RRR ~
C75 spec.

9. Material for C75 prototype cavities
Cavity
Ingot SN
Supplier
RRR
Ta content
(wt. ppm)
5C75-001
2370-5
CBMM
118
1350
5C75-002
2667-5
114
670
5C75-003
NC-1654
Tokyo-Denkai
496 29
Prototype single-cell cavities test results
2370-5
2667-5
NC-1654
Medium purity Nb ingots
Ingot Nb disc

10. C75 prototype cavities
Standard fabrication techniques (deep-drawing, machining, electron beam welding)
Improved cleaning of parts in preparation for welding
Inside/outside equator welds
5C75-001
5C75-002
5C75-003
70 mm CBP
95 mm BCP 1:1:2
30 mm EP
35 mm EP
600 °C/ 3 h vacuum anneal
800 °C/ 3 h vacuum anneal
20 mm EP
HPR
RF Test
Local grinding
30 mm BCP 1:1:2

11. Prototype cavity performance
Single-cavity test
Cavity pair configuration (HOM elbows and load, dog-leg, RF window, top-hat)
Losses due to metallization in RF window
Cavity pair type
C50
C75
Lorentz force detuning [Hz/(MV/m)2]
~ ‒3
~ ‒5

12. HOM analysis No HOM issues
TE111 and TM110 Qs measured on cavity pair at 4 K
Results are conservative since dog-leg + top-hat is not as broadband as in the cryomodule configuration to damp modes below 1.9 GHz
= (R/Q)calc Qmeas
No HOM issues

13. Weld defects
The gradient performance of the prototype cavities was limited by weld defects
Malfunctioning components in the EBW machine have been replaced
1 mm
1 mm
1 mm
5C75-001, cell 4
5C75-002, cell 4
5C75-003, cell 4

14. Tuner The original tuner will be used
Machining the profile of the cell holder clamps to fit new cell shape
Replacement of some components with high remanent field
Installation of new magnetic shield (Cryoperm 10®, 1 mm thick)
Cell Holder Assy Swivel (Inside Yoke Assembly)
Cell Holder Clamp
New magnetic shield

15. Tuning sensitivity
Tuning sensitivity measured with tuner and magnetic shield assembled both on a C20/C50 and a C75 cavity
Linear stiffness of cavities also measured
C50
C75
Tuning sensitivity (kHz/mm)
370 ± 40
470 ± 80
Stiffness (klbf/in)
24 ± 2
22 ± 3

16. Microphonics
Simulations show the presence of mechanical modes of vibration of C50 cavities with swaying of HOM waveguides near 60 Hz
Supports were designed to restrain the HOM waveguides to tuner cell holder
Hammer tests performed on C75 pair showed higher mode damping with support brackets installed
Accelerometer
HOM support

17. FPC transition waveguide
Operation with up to 8 kW forward power
Thermal performance demonstrated in FEL module FL02
Analysis required to confirm heat loads and thermal strap size to handle higher dynamic heat load than for C50
Re-use copper-plated SS FPC transition waveguide from existing CM and change heat station location
Not done for C75 pair in C50-13

18. Reducing CWVF trips Low conductance Low H2 pumping
Courtesy of M. Drury

19. RF Power Identical to the operational R100 installation 8 kW Klystron
Upgraded HV Power Supply
8 kW Circulators
New HPA controls
Digital LLRF control for operation with higher Qext and LFD

20. unit cost (FY16 M$ Direct)
Presented at Director’s Review on Jan. 21st 2016 and JLab’s upper management on Feb. 5th 2016
All costs in FY16 DIRECT Dollars
From Accelerator "STAY Treat" July2015) - see Slide 6
# Cav
cells /cav
cav length m
Active Length m
fill factor % MV
volts /cav (MV)
gradient (MV/m)
klystron power
unit cost (FY16 M$ Direct) RF
Cost
Total Cost FY16 Direct
MV (gain)
V(gain) /$
C50 8 5
0.5 4
48.1 50
6.25
12.5 6
1.51 20
13.3
C75† 75
9.4
18.8‡
1.91 45
23.6
C100‡ 7
0.7
5.6
64.4
100
17.9‡ 13
4.77 70
14.7
Update - January 2016
*RF Cost
1.23
16.3
1.73
0.77
2.50
18.0
4.30
1.56
5.85
12.0
†New cells or new processing required to achieve higher Q’s and gradients
‡Digital LLRF required
What changed from August 2015 to January 2016 ?
Addition of RF to C100 & C75 (assumes C50 still usable)
Updated Rates (Budget Office ) & change TDIII to TD II (match AWP)
Improved estimate for Fabrication and other costs
What is not included ?
One time R&D costs
Wave Guide Vendor Development + 8 Wave Guides
Courtesy of A. McEwen

21. Issues and open questions
Achieving Q0-spec in cryomodule
Not successful in C50 program
Main issues:
Shielding from or eliminating remanent magnetic field close to the cavity
Reduce/eliminate losses from metallization of cold window
Degaussing equipment for components, up to 66 kA/m
Will try degaussing of fully assembled cryounit in FEL04
New magnetic shield close to the cavities added in C50-7B (aka C50-13)

22. Issues and open questions
Cavity manufacturing
New electronics and updated controls for EBW machine
Sent RFQs to cavity manufacturers
Critical spares: there are no spares HOM loads
New HOM prototype successfully designed and built
Need to build small inventory
Applies to C50 rework

23. Issues and open questions
Critical spares: FPC transition waveguide
Very limited number of spare FPCs in inventory, none released for production
Forced to re-use FPCs that are of fair or poor quality  contributes to 2 K dynamic heat load
Currently no suppliers available that can produce new copies of this assembly
Applies to C50 rework
Need to develop new suppliers
Vendor development + 8 WGs: $360k (direct, FY16)

24. Issues and open questions
Cryogenic operation
If Q0-spec will be met, the heat load of C75 CM will be within ~10% of that of a current C50 CM
No changes expected in terms of hardware (heaters) or controls (CHL heat management software)

25. Issues and open questions
Expectations for C75 pair from commissioning of C50-7B (aka C50-13):
Operation of one cavity at 19 MV/m
Verification of tuner operation
Verification of new magnetic shields (all cavities)
A decision is missing on next module rework
Disassembly of old module and fabrication of 8 cavities should start NOW to be able to deliver a C75 module in August 2018

26. References Cavity Shape Cavity Material
H. Wang, R. Rimmer and G. Wu, “Elliptical Cavity Shape Optimization for Acceleration and HOM Damping”, Proc. PAC’05, Knoxville, TN, 2005, p
Cavity Material
P. Kneisel et al., Nucl. Inst. Meth. Phys. Res. A 774 (2015) 133–150.
G. Ciovati, P. Dhakal and G. R. Myneni, Supercond. Sci. Technol. 29 (2016)
P. Kneisel, “Progress on large grain and single grain niobium - ingots and sheet and review of progress on large grain and single grain niobium cavities”, Proc. SRF’07, Beijing, China (2007) p. 728.
G. Ciovati, P. Kneisel and G. R. Myneni, “America’s overview of superconducting science and technology of ingot niobium”, in Proc. of the Symposium on the Supercond. Sci. and Technol. of Ingot Niobium, AIP Conf. Proc (2011) p. 25.
G. Ciovati, P. Dhakal, P. Kneisel and G. R. Myneni, “Summary of performance of superconducting radio-frequency cavities built from CBMM niobium ingots”, in Science and Technology of Ingot Niobium for Superconducting Radiofrequency Applications, AIP Conf. Proc (2015)
W. Singer et al., Phys. Rev. ST Accel. Beams 16, (2013).
J. Sekutowicz et al., Phys. Rev. ST Accel. Beams 18, (2015).

27. References Cavity Fabrication and Tests
G. Ciovati et al., “Experience with the fabrication, processing and testing of the prototype “C75” 5-cell cavities”, JLab Tech Note TN (2017).
R. Rimmer et al., “Upgraded cavities for the CEBAF cryomodule rework program”, presented at SRF’17, Lanzhou, China (2017).
Microphonics, tuning sensitivity
K. Davis and T. Powers, “Microphonics Evaluation for the CEBAF Energy Upgrade”, JLab Tech Note TN-05-40, 2005.
G. Ciovati et al., “Tuning sensitivity and stiffness of C20/C50 and C75 cavities”, JLab Tech Note TN (2017).
Low Q issue
M. Drury et al., “Summary report for the C50 cryomodule project”, PAC 11 Proc., pp (2011).
R. L. Geng et al., “Pursuing the origin and remediation of low Q0 observed in the original CEBAF cryomodules”, Proc. IPAC’14, Dresden, Germany (2014) p
G. Ciovati et al., IEEE Trans. Appl. Supercond. 27 (4) (2017)

28. Backup slides

29. RF Power
Imax = 460 µA (max, beam loading), target Q0 = 8e9, HC 5-cell cavity R/Q= Ω
Eacc = MV/m for 75 MeV
Existing klystrons work at 8 kW just as for R100
Allow waveguide losses and linear working regime (-1dB) = 6.4 kW
8 kW
6.4 kW
min.
Measured peak microphonics for SL20 in CEBAF ( Hz, avg Hz)
Qext,opt = 20 Hz
Qext,opt = 25 Hz
Qext,opt = 20 Hz
range: e7