1. Rongli Geng ILC Cavity Group Meeting October 25, 2011
Cost Analysis of Cavity Production/Processing Strategies Based on Recent Gradient R&D Results
Rongli Geng
ILC Cavity Group Meeting
October 25, 2011
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

2. 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)
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

3. Baseline Cavity Fab. & Proc. Recipe
High purity sheet Nb forming and machining
Electron beam welding
Light BCP
Bulk EP
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
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

4. 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)
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

5. ILC 36th Cavity Group Meeting
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

6. 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”
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

7. ILC 36th Cavity Group Meeting
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?
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

8. ILC 36th Cavity Group Meeting
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

9. ILC 36th Cavity Group Meeting
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
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

10. ILC 36th Cavity Group Meeting
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
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

11. R&D Results since RDR - II
R&D results since RDR and understanding
A second pass re-treatment or re-processing is found effective in raising gradient and yield (good news)
100% yield at ≥ 31 MV/m is possible if a data-driven second pass re-treatment/re-processing is allowed (next slide)
Three main procedures (all in hand now) for second pass
Re-HPR, when cavity is field emission limited after 1st pass
Re-EP, when cavity reaches ≥ 25 MV/m but quench limited after 1st pass
Repair (local grinding or mechanical barrel polishing of entire inner surface), when cavity is quench limited below ~20 MV/m after 1st pass
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

12. 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
Rongli Geng
LCWS11, 9/26-30, 2008

13. ILC 36th Cavity Group Meeting
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
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

14. ILC 36th Cavity Group Meeting
Cost Benefit Analysis
Significant cost saving benefit
by allowing 25% 2nd pass re-treatment
or re-processing as compared to
allowing 25% over production
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

15. 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
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting

16. Next Step and Required Inputs
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
10/25/11, R.L. Geng
ILC 36th Cavity Group Meeting