1. Update on activities of investigations for analysis of module cavity degradation
Degradation and possible sources
Statistic of resonators
Analysis of log books
Analysis of hard ware
Status of RF tests on degraded resonators
Test results
Conclusions
Axel Matheisen, Denis Kostin, Detlef Reschke
TTC Meeting Beijing Dec 2011

2. Degradation
Degradation between last Q(E) in vertical acceptance test and module test => lot of handlings, treatment + assembly
Degradation by a) enhanced field emission with lower usable / maximum gradient => typically explained by particle contamination during handling or improper venting condition b) reduced quench gradient => ???
In vertical acceptance tests degradation sometimes seen due to a) field emission activation during first power rise (Q(E)-curve) b) after quenches at high fields (>35 MV/m) by some MV/m (cure by warming-up => indication by one older single-cell test) c) after FE-processing ??

3. Handlings, treatments, assembly
From vertical test to module test: - cleanroom assembly of power coupler - cleanroom connection of string - partially exchange of flanges (e.g. HOM feedthroughs) - HPR - partially tank welding (cavity stays closed) - several pumping and venting cycles

4. * Recruited for analysis
Statistics of Degraded Cavities
Module
Cavity
Pos
Preparation
Gradient drop
Module Gradient
(MV/m) 3*
S32(X) 2
EP+BCP 8 19
3**
Z102(X) 6 EP 9 22
AC116(X) 7
BCP flash 12
3***
AC118(X) 5 23
AC148(X)
Z85
Z92
Z101(Y) 1
Z109
BCP+EP
Z108(Y) 3 10
Z88(Y) 4 28
Z104 27
PXFEL1
Z100 13
PXFEL2
Z133 * 11 16
PXFEL3
Z88 * 18
AC127 *
S1 global
Z108* 20
CM1
Z89 17
AC73 15
(Y): Field emission loaded (X): No data of field emission available
* Recruited for analysis

5. Position of degraded Cavities
Position of Cavity in modules P1
P 2
P 3
P 4
P 5
P 6
P 7 P8
No of cavities position 2 5 1 4
Statistic of position of resonators showing reduced performance in modules
=> Position 3 + 6: ???
Remark: Leak check during string assembly after P4

6. Analysis of Logbooks for Z88, Z108, AC127, Z133
Storage Z108; Z88; AC127: - non-standard storage (=> out of cleanroom) during cleanroom shut down (in respect to the other cavities of Module S1 global and PXFEL-modules) - stored closed under vacuum - cleaned manually (no US-cleaning due to assembled power coupler)
Assembly procedures Z133; AC127; Z88: - No differences to other cavities in line found in assembly log book in respect of - particulates loading - assembly times - leakage found - RGA - Z108 ? People on place did not report on irregularities.

7. Analysis of hard ware Vacuum Z88 AC127 Z108 Accessories DESY Equipment
Leak rate
Z88
AC127
Z108
RGA OK
P total before Module
Accessories
Power coupler cold part after dismounting
Clean no sparks top no oxidation
Wait for analysis
HOM Antennas after dismounting
OK no irregularity
Flanges gaskets
Ok no irregularity
DESY Equipment
Ultrasonic bath
Non homogeneity
top bottom; also in use for cavities not showing degradation
Flange cleaning*
manual cleaning due to installed power couplers for reentering cleanroom
*New test set up developed not applied on these cavities yet

8. Status of RF tests on degraded cavities#
Test mode
Antenna
type
HOM installed
AC127 gradient Eacc max (Fe onset )
Z88 gradient Eacc max (Fe onset )
Z133 gradient Eacc max (Fe onset ) 1
Vertical HQ No
27,6 (27)
30,4 (30)
27,3 (20,5) 2
Module PC
Yes
19,2 (19)
18,5 (18)
16,2 (?) 3
CHECHIA
20,4 (19)
19,9 (18)
---- 4
-----
12,8 (11)* 5
19,7 (14)
  ----- 6
17,7 (13)
Mode analysis HD ??
Remove tank 7
T map
variable
wait
HQ = high Q antenna long pulse mode RF test
PC = power coupler operated with Klystron in pulse mode
Var= Variable antenna installed fro T map
* Limitation by HOM coupler

9. Q(E)-measurements of Z88

10. Q(E)-measurements of AC127

11. Up to now: NO proveable explanation for degradation w/o FE
Conclusion
Up to now: NO proveable explanation for degradation w/o FE
Vertical test with T-mapping and subsequent optical inspection of Z88, Z108 + AC127 in preparation