1. Performance of Superconducting Cavities for the European XFEL
Detlef Reschke – DESY for the EU-XFEL Accelerator Consortium
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2. Outline European XFEL Linear Accelerator Cavity Production
Vertical Acceptance Test
Cryomodule Test
Injector commissioning: GHz Injector Module GHz Third Harmonic System
cw R&D on XFEL Cryomodules

3. The European XFEL Built by Research Institutes from 12 European Nations
Headline
first level
second level
third level

4. Accelerator Complex for 17.5 GeV
accelerator modules
808 accelerating cavities
1.3 GHz / 23.6 MV/m
RF stations 5.2 MW each

5. Cavity production: Preparation Phase
Define final cavity design => TESLA design with minor design changes
Establishing surface treatment recipes => based on app. 50 prototype cavities
Industrialization of main Electropolishing surface treatment => set up of EP facilities at 2 companies
Single-cell cavity R&D program (several aims)
Preparation of detailed specifications => mechanical fabrication, surface treatment, HT integration, transport concept
Finalize a concept for documentation and data transfer
Qualification + selection of Nb / NbTi material vendors => 2 new companies
Concept for fulfilling PED requirements
Establishing “Long pulse” vertical acceptance test => protect HOM feedthroughs
R&D on Large Grain Nb material
Courtesy W. Singer

6. Cavity production
Contract allocated to Research Instruments (RI, Germany) and E.Zanon (EZ, Italy) in equal shares end 2010:
560 series cavities
24 cavities w/o He-tank for QC and further R&D (EU funded: “ILC-HiGrade”)
Option: 240 series cavity => Order allocated end 2012/beginning in equal shares
All Nb / NbTi material provided by DESY (~ pieces) => includes ordering, PED-applicable QC + parts tracking, shipment
Order placed following “Build-to-Print” strategy:
Production has to follow specifications precisely => close supervision by expert team + frequent visits + regular reporting (no resident expert at vendor)
No performance guarantee by vendors

7. Cavity Surface Preparation
Two schemes for the final surface treatment: - E. Zanon: Final 10µm BCP (“BCP Flash”) - Research Instr.: Final 40µm EP
Successful mechanical production and surface preparation at both vendors!
No performance guarantee resulted in DESY taking responsibility for:
the risk of unexpected low gradient or field emission
retreatment (good cooperation/agreements with both vendors)
Final EP
BCP Flash

8. Quality Management + Documentation
Key technical documents: Technical Specifications + Change Reports
Quality Process based on Quality Control Plan (also for PED) including:
Vendor internal QA, QM system
Microsoft Project Plan for tracking of progress + schedule
Non Conformity Reports NCR: Documentation of all NC’s including a proposal for correction procedure
Stepwise release of production (Acceptance Levels 1, 2, 3)
All production documents (specifications, protocols, PED data, etc.) recorded electronically in data management system (EDMS)
Data analysis in cavity data base
Request Tracked communication (“tickets”)
- RF test system - direct file transfer - (manual entry)
TUPOW001
Courtesy W. Singer

9. Transportation + Incoming Inspection9
Transportation + Incoming Inspection
Transportation:
“Cavity ready for test” requires well-defined transport concept
Transport under vacuum => avoid particle transport
Dedicated boxes for horizontal transport by truck (Vendor => DESY => Saclay)
No performance degradation observed
Incoming inspection at DESY
Basic mechanical, electrical, RF checks + final vacuum leak check before test
Idea: Check for damages during transport
Found: - Assembly errors + contaminations - Mechanical + electrical damages - Few leaks
Incoming Inspection is mandatory
Remark:
Additional and comprehensive information about NC‘s + experiences with QC concept during production extend this talk => aware that this is missing
=> 54 Cv‘s back to vendor

10. Vertical tests at AMTF

11. Statistics of Cavities + Vertical Acceptance Tests11
Statistics of Cavities + Vertical Acceptance Tests
Cavity production finished with last delivery in Mar 2016:
(800 + extra 4) Series Cavities
24 ILC “HiGrade”-Cavities (w/o He-tank; QC)
8 since equipped with He-tank and used for XFEL
16 Cavities for infrastructure commissioning
4 since used for XFEL
=> 816 cavities available and vertically tested for XFEL
Analysis of vertical acceptance tests includes
Series Cavities
ILC “HiGrade”-Cavities (w/o He-tank)
NO infrastructure commissioning tests
Stable average vertical test rate ~40 tests/month achieved
1225 vertical tests (few additional tests due to returns from string assembly possible)
- updated

12. VT-CM comparison: USABLE GRADIENT
Vertical Test – min of
Maximum gradient (quench, RF power)
FE limit (top/bottom X-ray)
Q0 limit (= 1010)
Cryomodule – min of
Maximum gradient (quench)
FE limit (front/back X-ray)
RF power limit at 31 MV/m
Acceptance criteria for “Usable gradient” in vertical test
INITIAL: > 26 MV/m (10% margin to required average design operating gradient)
NOW (after analysis of retreatment results in May 2014): > 20 MV/m (for optimized number of retreatments and retests)
No update necessary

13. Results: Usable Gradient “As received”
re-treat & retest
accept for module
Both vendors well above Spec
RI shows ~ 3MV/m in average more than EZ: a) final EP b) low gradient quenches at EZ
Several cavities with < 20 MV/m accepted “as received”, especially if a) limitation = “bd“ + b) no FE
Average Q-values for both vendors: Q0(4 MV/m) = 2.1·1010 Q0(23.6 MV/m) = 1.3·1010
Missing ~90 cavities “as received”?
updated

14. Good stability of average usable gradient over full production period
Trend of Usable Gradient “As received”
Good stability of average usable gradient over full production period

15. Retreatments
Why cavities w/o “as received” test? (“as received”: first test after delivery to DESY + cavity conform to Spec)
Three main categories for retreatment (rework):
Non-Conformities after delivery from vendor (~ 90 Tests) (mechanical, vacuum, defects, …) => retreatment/rework at DESY or vendor depending on NC-type
Performance (~160 Tests) (acceptance criteria for gradient or Q-value not met) mainly by field emission (+ “Quench”, “low Q”) => first + successful retreatment High Pressure Ultrapure Water Rinse <Eacc, usable>: 19 MV/m => 26 MV/m <Q0(4 MV/m)>: 2.1 · 1010 => 2.4 · 1010
Non-Conformity during string assembly (21 Cv)
- Categories for test purpose + formalized decisions according to test result

16. Analysis of Cavity Results16
Analysis of Cavity Results
Fully statistical approach; (nearly) no individual cavity analysis => simplified vertical test procedure at 2K: - Q0(Eacc), - fundamental mode spectra, - HOM-check (partially)
Work in progress: Analysis and possible correlations for Eacc,max, Q-value + x-rays
Nb-material: Vendor dependency
Cavity with vs. without He-tank
Surface treatment (not vendor)
Dependence on test infrastructure (RF test stand, cryostat, test inserts, …)
Cool down procedure => no special procedure applied, bad instrumentation, …
“Processing” vs. degradation in case of field emission; degradation after quench
Optical inspection, local repair …
Error analysis
- updated
WEPMB007

17. Finally: “Send to Saclay“17
Finally: “Send to Saclay“
(nearly) all cavities shipped to CEA Saclay for string assembly
average usable gradient: ~ 30 MV/m
includes cavities for three modules below 20 MV/m
Mainly low gradient quenches => retreatment not successful => retreatment would run out of schedule
Consequence of missing performance guarantee
> 810
- updated

18. Cryomodule Test at AMTF18
Cryomodule Test at AMTF
April, 20: 90 modules arrived with ~87 modules rf tested (XM-3 excluded)

19. Statistics of Cryomodules + Cryomodule Tests19
Statistics of Cryomodules + Cryomodule Tests
Cryomodule assembly at CEA Saclay (=> see SRF2015, O. Napoly)
Analysis of cryomodule tests: April 20, 2016 (~87 cryomodules)
Improved and optimized test procedure since June => typical test duration reduced to < 15 days (assuming no non-conformities!!!)
Non-conformities (causing significant delay): - cryogenic + vacuum leaks (mainly at temporary connections to test stand) - warm coupler part (“push rod” bellow leaks, assembly NC’s, …)

20. Cryomodule – Vertical Test Comparison: MAX GRADIENT
individual cavity comparison of max gradient
(upper limit due to 31 MV/m limit in module test)
we lose between vertical and cryomodule test
average VT: 30.3 MV/m (clipped at 31 MV/m) average CT: 28.7 MV/m (includes limit at 31MV/m)
Ideal case VT:CM = 1:1
Update necessary: average gradients to be checked

21. Vertical Test - Cryomodule Comparison: USABLE / OPERATIONAL GRADIENT
Vertical Test – min of
Maximum gradient (quench)
FE limit (top/bottom X-ray)
Q0 limit (= 1010)
RF power limit at ~200 W
Cryomodule – min of
Maximum gradient (quench)
FE limit (front/back X-ray)
not available
RF power limit at 31 MV/m P
(P)
when making comparisons, ?

22. Vertical Test - Cryomodule Comparison: Average cryomodule gradients
CM: upper limit due to 31 MV/m limit by RF power VT: clipped at 31 MV/m
Average VT performance met within <4%

23. Vertical Test - Cryomodule Comparison: Q0-values at ~20-23MV/m
estimated error of cryomodule Q-value: ~30%
Update of average Q-values necessary
Average Q0-value at ~20-23 MV/m: vertical ~1.4 x cryomodules ~1.4 x 1010

24. Cryomodule Operation in the Injector
Cold module operation started Dec 2015
More about “Commissioning of the European XFEL Injector” see F. Brinker & W. Decking: TUOCA03

25. Injector Module Performance: First “cold” 1.3 GHz module A1 (XM29)
=> not cavity limited
Courtesy D. Kostin
No cavity limitation during injector operation (up to 160 MeV beam energy)

26. 3.9 GHz Cavity Performances
VT of undressed cavities before integration and module assembly successful: Spec: <VT>: 20.8 > 109
Horizontal RF test of one fully equipped GHz cavity up to 24 MV/m: => Cavity package validated (tuner, coupler, WG tuners)
String assembly:
Courtesy P. Pierini

27. Third Harmonic module in XFEL injector
AH1 (3.9 GHz module) operating since the start of the Injector commissioning
Beam dynamics requirements: up to approx 30 MV
Successful tunnel operation: tested >45 MV tunnel RF test environment much less accurate (C7 is the first cavity to reach quench limit above VS setpoint of 45 MV)
Spare module in fabrication (with plans for CW tests)
Regular closed loop operation on beam since Dec 2015, typically at 20 MV
Cav
Eacc (MV/m)
XTIN VT C1
18.1
21.0 C2
17.6
20.0 C3
18.7
20.8 C4
17.1
22.0 C5
18.2 C6
19.6 C7
17.7 C8
17.3
21.8
First evidence of linearization effect
AH1 off
AH1 on
Courtesy P. Pierini
TUPOW005

28. cw R&D on EU-XFEL Cryomodules
EU-XFEL and FLASH originate from the TESLA collider and therefore they nominally operate (FLASH) and will operate (EU-XFEL) in so called short pulse (sp) mode
RF-pulses
Max RF DF [%]
Max RF pulse length incl. rise time [µs]
Rep. Rate [Hz]
1400 10
1.40
Both accelerators are based on the SRF technology and thus have potential for much larger DF, up to 100% (cw).
Having additional cw and long pulse modes will allow for more flexibility in the time structure of the photon beams and will make both facilities even more attractive to the users.
- updated
Courtesy J. Sekutowicz

29. cw R&D on EU-XFEL Cryomodules
Summary for series XFEL cryomodule in short pulse, long pulse (lp) and cw operation mode:
Courtesy J. Sekutowicz
Demonstrated Gradients
Mode sp lp cw
XM4 / FG
Max <Eacc> [MV/m]
31.8 19 15
Demonstrated Qo in lp/cw operation at 2K and 1.8K
Mode
lp (DF≈20%) cw
XM4 / FG
2.3E10 /
- updated
No quench was observed for cw/lp modes in all conducted tests.
Maximum demonstrated DHL was 71 W in cw mode at ~15 MV/m. Operation was very stable. This proves that the E-XFEL cryomodule helium supply and return system can handle at least 77W dissipation.

30. Summary + Outlook
Cavity production at both vendors successfully finished
Vertical acceptance tests finished and well above Spec
Accelerator cryomodule assembly and testing close to be finished
Cryomodule tests well above Spec (some degraded cavities after string assembly)
1.3 GHz injector cryomodule and 3.9 GHz third harmonic system in successful beam operation
Series 1.3 GHz cryomodule tested in cw / long pulse mode with excellent results
Detailed analysis of VT and CM tests for correlations in progress
EU-XFEL Linac commissioning in late 2016

31. Thanks to all colleagues of:
- IFJ-PAN Krakow (esp. J. Swierblewski, M. Wiencek)
- CEA Saclay
- INFN Milano (esp. L. Monaco)
- E. Zanon
- Research Instruments
- Daher Transkem
- Alsyom
- DESY (esp. V. Gubarev, J. Schaffran, L. Steder, N. Walker, M. Wenskat, S. Yasar)

32. :
- Back-up

33. Installation Progress XTL
Please use Hyperlink to view pictures
76 Modules installed 1 RF-Station ready
15 RF-Station in preperation
Status: 33
Injector
Dogleg
BC0
DEMACO Cryo-connection
CS1 L1
A2.1.L1
L001
A2.2.L1
L002
A2.3.L1
L003
A2.4.L1
L004
BC1
CS2 L2
A3.1.L2
L005
A3.2.L2
L006
A3.3.L2
L007
A3.4.L2
L008
XM 5
XM 1
XM 2
XM -1
DEMACO Cryo-connection
XM 62
XM 61
XM 71
XM 76
Tentative amplification of the Rack Shielding
Girder in BC Sections uncovered
Supports with Magnets A2 x P P P
Cryo stage A3
Cryo stage CR
CS2 L2
A4.1.L2
L009
A4.2.L2
L010
A4.3.L2
L011
A4.4.L2
L012
A5.1.L2
L013
A5.2.L2
L014
A5.3.L2
L015
A5.4.L2
L016
BC2
XM 73
XM 57 50
XM59
XM 72
XM44
XM 43
XM47
XM42
DEMACO Cryo-connection
Girder in BC Sections uncovered
XBG‘s & other Magnets x CR CR x A4 A5
Cryo stage 32
Cryo stage P
CS3 L3
A6.1.L3
L017
A6.2.L3
L018
A6.3.L3
L019
A6.4.L3
L020
A7.1.L3
L021
A7.2.L3
L022
A7.3.L3
L023
A7.4.L3
L024
A8.1.L3
L025
A8.2.L3
L026
A8.3.L3
L027
A8.4.L3
L028
XM 7
XM 6
XM11
XM 3
XM 13
XM 9
XM 10
XM 19
XM 27
XM 18
XM 30
XM 20
SCB 1 P P P 51 52 53 A6 54
UV XTL-2AV 55 56 57 A7 58 59 60 61 A8 P 62 63
CS4 L3
A9.1.L3
L029
A9.2.L3
L030
A9.3.L3
L031
A9.4.L3
L032
A10.1.L3
L033
A10.2.L3
L034
A10.3.L3
L035
A10.4.L3
L036
A11.1.L3
L037
A11.2.L3
L038
A11.3.L3
L039
A11.4.L3
L040
XM 31
XM 28
XM 34
XM 14
XM 39
XM 37
XM 40
XM 41
XM 26
XM 38
XM 36
XM 35
SCB 2 P
< < < HF-Tests in CS > > > P 64 65 66 A9 67 68 69 70
A10 71 72 73 74
A11
<<< Cleaning Tunnel >>> P 75 76
CS5 L3
A12.1.L3
L041
A12.2.L3
L042
A12.3.L3
L043
A12.4.L3
L044
A13.1.L3
L045
A13.2.L3
L046
A13.3.L3
L047
A13.4.L3
L048
A14.1.L3
L049
A14.2.L3
L050
A14.3.L3
L051
A14.4.L3
L052
XM 56
XM 32
XM 25
XM 53
XM 17
XM 51
XM 15
XM 52
XM 45
XM 16
XM 33
XM 49
SCB 3 P
< < < Rack cabling > > > P 77 78 79 x
A12 80 81 82 83 x
A13 P 84 85 86 87 x
A14 88 89
CS6 L3
A15.1.L3
L053
A15.2.L3
L054
A15.3.L3
L055
A15.4.L3
L056
A16.1.L3
L057
A16.2.L3
L058
A16.3.L3
L059
A16.4.L3
L060
A17.1.L3
L061
A17.2.L3
L062
A17.3.L3
L063
A17.4.L3
L064
XM 64
XM 68
XM 70
XM 21
XM 69
XM 60
XM 63
XM 66
XM 12
XM 23
XM 58
XM 48
SCB 4 P
< < < Rack cabling > > > P 90 91 x
A15 93 94 95 96 x
A16 P 97 98 99 P
100 x
A17
101
102 P
CS7 L3
A18.1.L3
L065
A18.2.L3
L066
A18.3.L3
L067
A18.4.L3
L068
A19.1.L3
L069
A19.2.L3
L070
A19.3.L3
L071
A19.4.L3
L072
A20.1.L3
L073
A20.2.L3
L074
A20.3.L3
L075
A20.4.L3
L076
XM 78
XM 80
XM 81
XM 75
XM 77
XM 74
XM -2
XM 79
XM 4
XM 67
XM55
XM65
SCB 5
Welding Module connections
Cryo stage
Cryo stage
Cryo stage
Cryo stage
Cryo stage
Cryo stage
CS8 L3
A21.1.L3
L077
A21.2.L3
L078
A21.3.L3
L079
A21.4.L3
L080
A22.1.L3
L081
A22.2.L3
L082
A22.3.L3
L083
A22.4.L3
L084
A23.1.L3
L085
A23.2.L3
L086
A23.3.L3
L087
A23.4.L3
L088
Container for condensed water
325 ltr.
1.508 m
CS9 L3
A24.1.L3
L089
A24.2.L3
L090
A24.3.L3
L091
A24.4.L3
L092
A25.1.L3
L093
A25.2.L3
L094
A25.3.L3
L095
A25.4.L3
L096
A26.1.L3
L097
A26.2.L3
L098
A26.3.L3
L099
A26.4.L3
L100

34. Third Harmonic module in XFEL injector
AH1 (3.9 GHz module) operating since the start of the Injector commissioning
Beam dynamics requirements: up to approx 30 MV
Successful tunnel operation: tested >45 MV tunnel RF test environment much less accurate (C7 is the first cavity to reach quench limit above VS setpoint of 45 MV)
Spare module in fabrication (with plans for CW tests)
Regular closed loop operation on beam since Dec 2015, typically at 20 MV
Cav
Eacc (MV/m)
XTIN VT C1
18.1
21.0 C2
17.6
20.0 C3
18.7
20.8 C4
17.1
22.0 C5
18.2 C6
19.6 C7
17.7 C8
17.3
21.8
Courtesy P. Pierini
TUPOW005