Vacuum leak

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THERMAL CYCLE TESTS OF RF WINDOWS
IN STF INPUT COUPLERS
2010/12/07
Masato 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
2
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
3
STF-1: CM test for 4 cavities
Input Coupler located from 300K to 2K
supplies RF power into SC-cavities.
Cross-section of CM
Warm Side
Input Coupler
2.0K
Nb-cavity
Cold Side
Warm window(300K)
Cold window(80K)
4
Input coupler
Warm window
Cold window
Input power in ILC
Eacc = 31.5MV/m
Beam current = 9mA
Pin = 300 kW
Warm window
1E-6 Pa
Cold Window
Cold window
5E-7 Pa(IP)
Choke:
To protect brazing part from strong
electric field, and to match
impedance at RF window
Coaxial
ceramic disk
Cu
Brazing
Between ceramics and Cu
5
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 cycles
No.1, No.3, No.4 couplers ・・・ 2 ones
6
Vacuum leak at cold windows
Warm Window
Cold Window
4 warm window at 300K
occurred 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)
7
Confirmation of vacuum leak
(1st : vacuum leak check)
2 cold couplers were installed in vacuum chamber
Leak detector
Vacuum pump
8
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
2.0E-04
Vacuum leak on inner brazing
for all the 3 couplers
Scan pitch:3mm
9
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
10
Linear Thermal Expansion Coefficient of Cu, Ceramics, Mo
Actual shrinking amount : - Δ length=length×∫LTEC dT
Thermal cycles  NG

Cool down  OK
 LTEC (T ) dT
300
80
LTEC (T ) dT
1200
300
3.0E-05
2.5E-05
2.0E-05
1.5E-05
1.0E-05
5.0E-06
0.0E+00
LTEC
2.7×10-3
16.6×10-3
Al2O3
Cu
Mo
7.46×10-3
0.65×10-3
5.39×10-3
0
0.89×10-3
500
Temp/K
1,000
1,500
Some measures against the thermal strain
Cu pipe can absorb the
thermal strain !
The original was designed by
Noguchi san and Toshiba.
11
Mo-Ring(Toshiba)
To reduce the strain of different material bonding
It was developed for Tristan input couplers in 1988
300K
Mo-ring is brazed
with ceramic disk at
the same time
Al2O3
Cu
1200K
Al2O3
300K
1200K  300K
Al2O3
Cu
Mo
Cu
12
Need to improve inner brazingSample windows #1,#2
2009/Sep.~ Oct. (S1-G already running)
Sample windows
The design was changed by Noguchi & Kako
Mo-ring
#2
#1
(ratio =0.8)
(t1.0)
Cu-Pipe
Stress∝(厚度)3  Ratio3 =0.83 ~0.5
:to make stress half
13
300K  77K cooling process
Thickly cover Samples by
Al foil(16P)
Indivisually put 3 TC on Samples
4
1
5
6
2
3
8
#2
#1
Temperature Change
#2
#1
Leak Check after Cooling
14
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
15
The improved ones are installed
in S1-Global, and they have no
trouble by now.
16
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
17
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