1. Explosive Events during V.T. in KEK ECFA LCWS13@DESY (2013/5/30) 1

2. 2 Sequence of cavity process Optical inspection f 0 & Field flatness measurement surface treatment (bulk EP ∼ 100 μ m) annealing pre-tuning V.T. as received from a vendor Optical inspection surface treatment (light EP ∼ 2-20 μ m, Degreasing, HPR) Cryomodule test failure success ☠ F.F. > 96%

3. ECFA LCWS13@DESY (2013/5/30) 3 MHI-14

4. ECFA LCWS13@DESY (2013/5/30) 4 Q 0 -E acc Curve for MHI #14 @1.8K & 4.2K 9.1MV/m power limit 26.0MV/m  14.1MV/m 15.0MV/m Cell #8 heating

5. ECFA LCWS13@DESY (2013/5/30) 5 Radiation Level in π mode measurement @2K

6. ECFA LCWS13@DESY (2013/5/30) 6 Iris between Cell#8-#9 278°

7. ECFA LCWS13@DESY (2013/5/30) 7 At this time, we didn’t believe this defect was problematic. Then, we did the same surface treatment, not local grinding.

8. ECFA LCWS13@DESY (2013/5/30) 8 Q 0 -E acc Curve for MHI #14 @1.8K & 4.2K 9.0MV/m power limit 25.9MV/m  12.4MV/m 13.0MV/m Cell #8 heating

9. ECFA LCWS13@DESY (2013/5/30) 9 Radiation Level in π mode measurement @2K

10. ECFA LCWS13@DESY (2013/5/30) 10 History of Iris 280° between Cell#8-#9 EP1 後 よく見ると兆候はある 1 st V.T. 後 2 nd V.T. 後 Still there!

11. ECFA LCWS13@DESY (2013/5/30) 11 At this time, we believe this defect was problematic. Then, we did the local grinding for the removel.

12. ECFA LCWS13@DESY (2013/5/30) 12 Q 0 -E acc Curve for MHI #14 @1.8K & 4.2K 8.5MV/m power limit 36.5MV/m Power limit 36.6MV/m Power limit

13. ECFA LCWS13@DESY (2013/5/30) 13 Radiation Level in π mode measurement @2K

14. ECFA LCWS13@DESY (2013/5/30) 14 MHI-15

15. ECFA LCWS13@DESY (2013/5/30) 15 Q 0 -E acc Curve for MHI #15 @1.8K & 4.2K 9.5MV/m power limit Q t = 6.81 x 10 10 → 6.42 x 10 10 32.3MV/m He pressure 33.5MV/m  18.4MV/m Explosive event occurred 18.1MV/m Self-pulse

16. ECFA LCWS13@DESY (2013/5/30) 16 Radiation Level in π mode measurement @2K

17. ECFA LCWS13@DESY (2013/5/30) 17 3-4 iris, θ=261~262° 8-9 iris, θ=277~286°

18. ECFA LCWS13@DESY (2013/5/30) 18 Type II: Defect on bead of Iris MHI-06, 09, 14, 15, 18, 19, 20, 22 and HIT-02 were limited by Type II. MHI-14MHI-15MHI-18 MHI-22MHI-20MHI-09 When a cavity has such a defect at iris region, the heavy field emission certainly occurs. 20.8MV/m (explosion) 18.1MV/m (explosion) 9.7MV/m 9.0MV/m 31.5MV/m 27.0MV/m (explosion)

19. ECFA LCWS13@DESY (2013/5/30) 19 What is different between DESY and KEK? ① In KEK, only EP process is used, never BCP. ② Problematic defect appears suddenly after EP. ③ It can not be removed by only EP (HPR), because of the mechanical structure. I doubt the BCP as one possibility.

20. ECFA LCWS13@DESY (2013/5/30) 20 Thank you for your attention.