thermal cycle tests of rf windows in stf input couplers
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THERMAL CYCLE TESTS OF RF WINDOWS IN STF INPUT COUPLERS
2010/12/07Masato Satoh
(KEK)
1
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
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STF-0.5, STF-1(2007 ~ 2008)
STF-0.5(2007) : 1 cavitySTF-1(2008) : 4 cavities
S1-G(now on) : 8 cavities
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Cryomodule tests
STF-1: CM test for 4 cavities
Cold window(80K)
Cold Side
Warm SideInput Coupler
Nb-cavity2.0K
Warm window(300K)
Input Coupler located from 300K to 2K supplies RF power into SC-cavities.Cross-section of CM
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Input coupler
Cold window
5E-7 Pa(IP)1E-6 PaWarm window
Cold Window
Coaxial ceramic disk
Cu
BrazingBetween ceramics and Cu
Choke :To protect brazing part from strong electric field, and to match impedance at RF window
Eacc = 31.5MV/mBeam current = 9mAPin = 300 kW
Input power in ILC
Warm window Cold window
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The cooling tests• STF-0.5 : cryomodule tests for 1 cavity– 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 cyclesNo.1, No.3, No.4 couplers ・・・ 2 ones
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Vacuum leak at cold windows
Cold window : RT ~ 80K3 couplers vacuum leak1 coupler no leak
Vacuum leak was caused by thermal cycles. One potential reason might be bonded between different materials.
4 warm window at 300K occurred vacuum leak
Warm Window Cold Window
Pin :130~270kW(20~30MV/m)
2×1 0-4 Pa m3 /s
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Confirmation of vacuum leak( 1st : vacuum leak check )
Vacuum pump
Leak detector
2 cold couplers were installed in vacuum chamber
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Sniffer test (sniff:嗅)φ6
No vacuum leak on outer brazing
Vacuum leak on inner brazing for all the 3 couplers
Scan pitch:3mm
0 deg
Sensitivity:5E-8 Pam^3/s
Cut down choke part
2.0E-04
Sniffer probe
Result of sniffer check
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Results of color check (No.1,No.3)
No.1 Coupler No.3 Coupler
R12
C1 C2
There were color reactions and cracks !
65°
239°
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0 500 1,000 1,5000.0E+005.0E-061.0E-051.5E-052.0E-052.5E-053.0E-05
Al2O3 Cu Mo
Temp/K
LTEC
Linear Thermal Expansion Coefficient of Cu, Ceramics, Mo
Cu pipe can absorb the thermal strain !
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300
1200)( dTTLTEC
80
300)( dTTLTEC
16.6×10-3
7.46×10-3
5.39×10-3
0.65×10-3
2.7×10-
3
0.89×10-
3
Actual shrinking amount : - Δ length=length×∫LTEC dT
The original was designed by Noguchi san and Toshiba.
Cool down OKThermal cycles NG
Some measures against the thermal strain
Mo-Ring ( Toshiba )300K 1200K 300K 1200K 300K
CuAl2O3
Cu
Al2O3Cu
Mo
To reduce the strain of different material bondingIt was developed for Tristan input couplers in 1988
Mo-ring is brazed with ceramic disk at the same time
Al2O3
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Need to improve inner brazingSample windows #1,#2 2009/Sep. ~ Oct. (S1-G already running)
#2 #1
Mo-ring
( t1.0)Stress∝ (厚度)3 Ratio 3 = 0.8 3 ~0.5: to make stress half
(ratio =0.8)
The design was changed by Noguchi & Kako
Cu-Pipe
Sample windows
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300K 77K cooling process
#2 #1 #1
4 1 5 6 2 3
#2
Indivisually put 3 TC on Samples
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Leak Check after Cooling
Thickly cover Samples by Al foil(16P)
Temperature Change
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Results of thermal cycles
#1: Mo,0.25t#2: Mo,0.20t
#3 and #4 same as #1 have been exposed in 22 thermal cycles No vacuum leak
Sample #1, #2 (2009 Sep ~ Oct)
Sample #3, #4 (2010 Apr ~Jun)
Type-#1 was adopted in S1-Global
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The improved ones are installed in S1-Global, and they have no trouble by now.
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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
- #1 Cu Pipe= 0.8t , Mo =0.25t had No 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 22 thermal cycle tests
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