THERMAL CYCLE TESTS OF RF WINDOWS IN STF INPUT COUPLERS

2010/12/07Masato Satoh

(KEK)

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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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