1. Rongli Geng Jefferson Lab & GDE
Cavity Gradient
Rongli Geng
Jefferson Lab & GDE
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

2. GDE SCRF Meeting, Beijing
Charge by SCRF PM
Scope for improving gradient
Production yield and variations assumed
Degradation after cavity string assembly
Scope for 1 TeV
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

3. GDE SCRF Meeting, Beijing
Scope for improving gradient
Production yield and variations assumed
Degradation after cavity string assembly
Scope for 1 TeV
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

4. Scope for Improving Gradient
Continue standard processing and testing in CY12
Resource limitation likely to impact data generation rate
JLAB: 12 GeV CEBAF upgrade project and TEDF transition
DESY
How many XFEL production cavities expected?
How many “non-project” cavities expected?
KEK:
FNAL: should we add FNAL’s data in yield analysis?
Continue cavity repair and testing
Cavity candidate and head count
Will Cornell continue?
Complete testing 10(?) cavities by using CBP for bulk removal at FNAL
Can one anticipation CBP will be inserted into the TDR recipe?
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

5. Scope for Improving Gradient
Continue automatic cavity optical inspection at DESY
Continue alternate cavity effort
JLab:
build a 9-cell LSF cavity
test DESY seamless 9-cell Z163, Z164 and BL
process and test large-grain 9-cell cavities
Process and test ICHIRO8
Cornell: continue re-entrant cavity processing and testing
KEK: what’s next for ICHIRO cavity?
IHEP: Low-loss cavity
Continue vendor qualification
FNAL
AES qualified
More to come: Niowave-Roark, Pavac
KEK
MHI qualified
More to come: Toshiba, Hitachi
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

6. Scope for Improving Gradient
EBW optimization
KEK pilot plant
Cavities count?
Scope?
EBW porosity?
JLab welding sample study
Aim at understanding of porosity in bulk
Plan to collaborate with KEK for material/sample exchange
X-ray imaging of EBW joint
KEK detector validation and system design
when the first result is expected
FNAL will continue
Material inspection and correlation
FNAL new procedure and spec based on EBSD?
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

7. GDE SCRF Meeting, Beijing
Scope for improving gradient
Production yield and variations assumed
Degradation after cavity string assembly
Scope for 1 TeV
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

8. ILC Cavity Gradient Design Values
Average operational 31.5 MV/m
Allowable spread up to ±20% (25.2 – 37.8 MV/m)
Average vertical test qualification 35 MV/m
Acceptable spread up to ±20% (28 – 42 MV/m)
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

9. Baseline Cavity Fab. & Proc. Recipe
High purity sheet Nb forming and machining
Electron beam welding
Light BCP
Bulk EP
(KEK: defect identification and preventive correction)
Vacuum furnace heat treatment
Rinsing
Field flatness tuning
Final light EP
Post-EP cleaning and high pressure water rinsing
Clean room assembly, evacuation and leak check
In-situ low temperature bake
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

10. R&D Results since RDR - I
RDR goal: achieve ≥35 MV/m with 80% production yield
R&D results since RDR and understanding
~ 20% of cavities will fail at 20 MV/m or lower due to fabrication/material defect (bad news)
Yield after one pass processing (or the typical definition of production yield) demonstrated on a global basis
at ≥35 MV/m is ~ 30%
at ≥28 MV/m, ~ 70%??? (Present global yield plot does not contain yield information at ≥28 MV/m – this should be fixed because 28 MV/m is an important number, i.e. the minimum acceptable gradient for vertical test)
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

11. GDE SCRF Meeting, Beijing
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

12. Cost Analysis of the Over Production Model
RDR assumes 25% over production (OP), based on assumption of 80% production yield (i.e. the yield after one pass processing) at ≥35 MV/m
Total number of cavities need N
Total number of cavities produced 1.25*N
Total cavities accepted 1.25*N*0.8=1.00*N=N
Ideal model for mass production
Tolerate 25% produced cavities being “thrown away”
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

13. GDE SCRF Meeting, Beijing
Consideration of the Over Production Model for the Present Cavity Gradient and Spread Design Choice
Current ILC design gradient and spread for vertical test acceptance: average 35 MV/m with allowable spread of up to ±20% (28 – 42 MV/m)
This is equivalent in stating that cavities qualified to ≥ 28 MV/m are all acceptable
Even though the present yield at ≥ 28 MV/m is less than 70% on a global bases, one may expect a yield of 80% at ≥ 28 MV/m can be achieved (next slide)
Then the question arises: can we stick to the 20-25% over-production model in line with the RDR?
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

14. GDE SCRF Meeting, Beijing
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

15. GDE SCRF Meeting, Beijing
Consideration of the Over Production Model for the Present Cavity Gradient and Spread Design Choice (continued)
Cost of an accepted cavity: C = Cf + Cp
Cf: Fabrication cost
Cp: Processing cost
Normalize cost to Cf
Typical ratio of Cp/Cf=0.2
Based on cost analysis of “production style” ILC cavity processing at JLab (spread sheet available) and typical present day fabrication cost of 9-cell cavities based on small orders
For future high-volume production, both Cf and Cp may go down due to value engineering, but the Cp/Cf ratio likely to stay ~0.2
So C=1.2*Cf
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

16. GDE SCRF Meeting, Beijing
Consideration of the Over Production Model for the Present Cavity Gradient and Spread Design Choice (continued)
C=1.2*Cf
25% over production
Total number of cavities produced 1.25*N
Total cost to get needed cavities
TC_OP=1.25*N*1.2*Cf = 1.50*N*Cf
Reminder: tolerate 25% of produced cavities are “thrown away” after one pass processing
Ultimately one needs to know the Gradient Distribution Probability (GDP) to verify whether the current ILC gradient spread choice is compatible with the ILC average gradient choice
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

17. GDE SCRF Meeting, Beijing
Effective gradient yield improvement if a 2nd pass RT/P is allowed 16 9-cell cavities based on recent results from US ART groups
94%
JLAB + FNAL + Cornell
Average gradient 39 MV/m
100% yield at ≥31 MV/m
Average gradient 39 MV/m
AES6 after CBP
At FNAL ✔
AES5 After
Mechanical
Polishing
at Cornell
ACC15 after
at FNAL
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

18. GDE SCRF Meeting, Beijing
Consideration of the Re-treatment Model for the Present Cavity Gradient and Spread Design Choice
Reminder: realistically assuming 80% yield at ≥ 28 MV/m after 1st pass
Reminder: 100% yield at > 28 MV/m if a data-driven second pass re-treatment/re-processing (RT/P) is allowed
Cost analysis if 2nd pass RT/P is allowed
Total number of cavities produced N
Same as the total number of cavities needed
80% of cavities acceptable after 1st pass
20-25% need 2nd pass RT/P to become acceptable
Total cost to get needed cavities (assuming 25% RT/P)
TC_RT/P=N*(Cf+Cp)+0.25*N*Cp = N*Cf+1.25*N*Cp=N*Cf+1.25*N*0.2*Cf
TC_RT/P= 1.25*N*Cf
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

19. GDE SCRF Meeting, Beijing
Cost Benefit Analysis
Significant cost saving benefit
by allowing 25% 2nd pass re-treatment
or re-processing as compared to
allowing 25% over production
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

20. Additional Benefit from RT/P
Further analysis requires knowledge of gradient distribution of probability p(G) p
RT/P tends to push p(G) upward, hence higher average gradient 1 G Gr Gu
Gr: Rejection limit, below which cavity not acceptable
Gu: ultimate limit, above which physically not possible
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

21. Conclusion and Next Step
Cost benefit analysis favors Re-Treatment/Processing (RT/P) model over Over Production (OP) model
Get GDP from the available data
This allows to calculate average gradient
Needed for “gradient margin” analysis
Get breakdown table of RT/P fractions
Needed for refined cost benefit analysis
Useful for RT/P strategy to be reflected in TDR
Get cost spread sheet for CBP
Needed for analysis of cost saving potential to insert CBP into baseline processing recipe
Question: does it make sense to allow 3rd RTP?
What experiment is needed?
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

22. GDE SCRF Meeting, Beijing
Scope for improving gradient
Production yield and variations assumed
Degradation after cavity string assembly
Scope for 1 TeV
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

23. GDE SCRF Meeting, Beijing
First order of business: categorize and improve understanding
Lots of discussion this morning
Data set still too small
All labs should start quantify the degradation
Field emission onset from vertical testing to horizontal testing
Collaboration with TTC
Cryogenic radiation detection
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

24. GDE SCRF Meeting, Beijing
Scope for improving gradient
Production yield and variations assumed
Degradation after cavity string assembly
Scope for 1 TeV
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

25. GDE SCRF Meeting, Beijing
From the point view of site AC power, pushing gradient beyond 35 MV/m requires raising Q0
45 MV/m at Q0 2E10 for 1 TeV ILC
Is this a worthy goal?
Key questions for moving forward
Path way?
Large-grain + new shape (LL, RE, LSF)
Nb-Cu clad material (seamless forming)
How to include coating of new material?
Field emission?
New technology beyond HPR?
HOM?
Lorentz force detuning?
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

26. GDE SCRF Meeting, Beijing
Backup Slides
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

27. Yield Definition – 1st-Pass
First-pass processing following “ILC recipe”
If cavity qualified (35 Q0≥8E9) by first-pass, stop further proc.
Different from “tight-loop” (earlier S0 approach)
Qualified cavity move on for S1
Failed proc./test due to known facility error excluded
If cavity not qualified by first-pass then 2nd-pass
ILC Processing & Testing Recipe (major steps)
Heavy EP
Vacuum furnace heat treatment
Light EP
Post-EP cleaning
HPR and clean room assembly
In-situ bake 120Cx48hr
Cool down to 2K
RF test
(Further test with T-mapping)
(Optical inspection for defect)
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

28. Yield Definition – 1st-Pass Yield
# of cavities passing Eacc
at 1st-pass processing
N(Eacc)
FPY(Eacc) =
N_tot
1st-pass yield at Eacc
# of cavities counted for yield
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

29. Yield Definition – 2nd -Pass
First-pass test result drives second-pass processing (including treatment other than just EP)
If cavity qualified by second-pass, stop further proc.
Qualified cavity move on for S1
Failed proc./test due to known facility error excluded
If cavity still not qualified by 2nd-pass then further decision
Possible second-pass treatments:
For FE limited cavity in 1st-pass
Re-HPR
Re-EP + 120cx48hr
For quench limited cavities in 1st-pass
Re-EP +120cx48hr
Local grinding + re-EP +120cx48hr
Tumbling + re-HT + re-EP + 120Cx48hr
Local e-beam re-melting (+ re-EP +120Cx48hr)
Local laser re-melting (+ re-EP +120Cx48hr)
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

30. Yield Definition – 2nd -Pass Yield
# of cavities passing final gradient
of Eacc up to 2nd-pass proc.
2nd-pass yield at Eacc
N2,1(Eacc)
SPY(Eacc) =
N_tot – N_no_spp
# of cavities
counted for yield
# of cavities requiring 2nd –pass proc.
but 2nd-pass processing not done yet
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing

31. Data Cut for Yield Analysis
No ACD cavities
LL/RE
Large-grain
No BCP processing
For damage layer
Or for final chemistry
Only cavities manufactured
by experienced vendors
ACCEL/RI
ZANON
AES
MHI
Despite these cut, still known large variability in fab and proc
Large number of cavities required to reduce statistical error
Some variability may be facility specific
12/8/11 Rongli Geng
GDE SCRF Meeting, Beijing