THERMAL CYCLE TESTS OF RF WINDOWS IN STF INPUT COUPLERS

THERMAL CYCLE TESTS OF RF WINDOWS IN STF INPUT COUPLERS 2010/12/07 Masato Satoh (KEK)

CONTENTS • STF-1（Cryomodule tests with 4 cavities） • Input coupler（structure and specifications） • Vacuum leak at low temperature • S1-Global • Detail of vacuum leak(sniffer & color check) • Thermal cycle tests with sample windows • Summary

STF-0.5, STF-1(2007～2008) Cryomodule tests STF-0.5(2007) : 1 cavity STF-1(2008) : 4 cavities S1-G(now on)：8 cavities

STF-1: CM test for 4 cavities Input Coupler located from 300K to 2K supplies RF power into SC-cavities. Cross-section of CM Input Coupler Warm Side 2.0K Nb-cavity Warm window(300K) Cold Side Cold window(80K)

Input coupler Warm window Warm window Cold window 5E-7 Pa(IP) 1E-6 Pa Choke： To protect brazing part from strong electric field, and to match impedance at RF window Cold Window Cold window Coaxial ceramic disk Input power in ILC Eacc = 31.5MV/m Beam current = 9mA Pin = 300 kW Cu Brazing Between ceramics and Cu

The cooling tests • STF-0.5 : cryomodule tests for １cavity • Cooling: 2007/10/3 ~ 2007/11/22 • STF-1: cryomodule tests for 4 cavities • 1st cooling: 2008/5/21 ~ 2008/7/25 • ２Ｋ　Low power test • 2nd cooling: 2008/9/9 ~ 2008/12/19 • ２Ｋ　High power test No.2 coupler　・・・　3 thermal cycles No.1, No.3, No.4 couplers　・・・　2 ones

Vacuum leak at cold windows Warm Window Cold Window 4 warm window at 300Koccurred vacuum leak Cold window : RT～80K 3 couplers  vacuum leak 1 coupler  no leak 2×1 0-4 Pa m3 /s Vacuum leak was caused by thermal cycles.  One potential reason might be bonded between different materials. Pin :130~270kW(20~30MV/m)

Confirmation of vacuum leak（1st : vacuum leak check） 2 cold couplers were installed in vacuum chamber Leak detector Vacuum pump

Sniffer test（ｓｎｉｆｆ：嗅） Cut down choke part Sniffer probe No vacuum leak on outer brazing Sensitivity:5E-8 Pam^3/s φ6 0 deg Result of sniffer check Vacuum leak on inner brazing for all the 3 couplers 2.0E-04 Scan pitch:3mm

Results of color check (No.1,No.3) There were color reactions and cracks！ No.1 Coupler No.3 Coupler 239° 65° C1 C2 R12

Linear Thermal Expansion Coefficient of Cu, Ceramics, Mo Actual shrinking amount : - Δ length=length×∫LTEC dT Thermal cycles  NG Cool down  OK 16.6×10-3 2.7×10-3 7.46×10-3 0.65×10-3 5.39×10-3 0.89×10-3 Some measures against the thermal strain Cu pipe can absorb the thermal strain ! The original was designed by Noguchi san and Toshiba.

Mo-Ring（Toshiba） To reduce the strain of different material bonding It was developed for Tristan input couplers in 1988 300K 1200K 300K 1200K  300K Al2O3 Al2O3 Al2O3 Mo Cu Mo-ring is brazed with ceramic disk at the same time Cu Cu

Need to improve inner brazingSample windows#1,#2 2009/Sep.～ Oct. (S1-G already running) The design was changed by Noguchi & Kako Sample windows Mo-ring #2 #1 (ratio =0.8) （t1.0） Cu-Pipe Stress∝（厚度）３ Ratio３＝0.8３　～0.5 ：to make stress half

300K  77Kcooling process Thickly cover Samples by Al foil(16P) Indivisually put 3 TC on Samples 4 1 5 2 6 3 8 #2 #1 #2 #1 Leak Check after Cooling Temperature Change

Results of thermal cycles Type-#1 was adopted in S1-Global Sample #1, #2 (2009 Sep ～Oct) #1: Mo,0.25t #2: Mo,0.20t Sample #3, #4 (2010 Apr ～Jun) #3 and #4 same as #1 have been exposed in 22 thermal cycles  No vacuum leak

The improved ones are installed in S1-Global, and they have no trouble by now.

Summary • STF-0.5&1 cryomodule tests were carried out, -Vacuum leak happened on 3 cold windows which had Cu Pipe= 1.0t, Mo = 0.25t • Samples #1,#2 were made, and applied 6 thermal cycles - #1Cu Pipe= 0.8t , Mo =0.25t hadNo vacuum leak Type-#1 was adopted for S1-G cryomodule test #2 Cu Pipe = 0.8t , Mo =0.20t happened Vacuum leak • Sample #3, #4 same as #1 No vacuum leak against 22thermal cycle tests

THERMAL CYCLE TESTS OF RF WINDOWS IN STF INPUT COUPLERS