IR Vacuum
From the first anomaly to the final
large helium leak
KEKB Accelerator Review
10-11 February 2003
K. Kanazawa

Location of vacuum gauges (L-side)

H-02A

Location of vacuum gauges (R-side)

The reading of H24 is about 1/10 of an
actual pressure due to the solenoid
field of Belle.

CCG_H01A
CCG_H02
CCG_H02A

CCG_H23
CCG_H23A
CCG_H24

DCCT:HER
DCCT:LER

30-31 Oct.
-410Abnormally highdynamic pressure

1st pressure burst

4000

10-6

3000

10-7

2000

10-8

10-9
10/30/2002
9:00:00

1000

10/30/2002
15:00:0010/30/2002
21:00:00
time

10/31/2002
3:00:00

010/31/2002
9:00:00

Beam Current [mA]

Pressure [Pa]

10-5

5000

In the earlymorning of 31Oct., anabnormalpressure wasnoticed at IP.
On therecord it was
found that theanomaly ofpressure
began the day
before.
From 9:30 of31 Oct., westarted theleak test for
the IR.

Detail of 31 0ct. 2h-4h.
CCG_H01A
CCG_H02

CCG_H23
CCG_H23A

CCG_H02A

CCG_H24

DCCT:HER
DCCT:LER

31 Oct. 02h - 04h-5

104000pressure spikePressure [Pa]

3000

2000
abnormal dynamic pressure
10-7step-wiseincrease ofthe basepressure-8

1010/31/2002
2:00:00

10/31/2002
3:00:00time

1000

010/31/2002
4:00:00

Beam Current [mA]10-6

Leak Test on 31 Oct.

•••

•

•

The outgassing around IP was oneorder higher than usual. But...
No leakage was detected by splaying
helium from outside.
A small helium peak (1/1000 of thehydrogen peak) was observed by RGA(left picture). The identification of thesource of this helium peak was notdone because it cannot explain a largepressure rise.
The amount of hydrogen was
gradually increasing during the leak
test, which seemed to correspond tothe gradual increase of the basepressure.
Conclusion––

No detectable leak.
The phenomena looks as if a fresh
surface appeared near IP.

CCG_H01A
CCG_H02
CCG_H02A

CCG_H23
CCG_H23A
CCG_H24Since noleakage wasfound, beam
scrubbing wastried.

DCCT:HER
DCCT:LER

31 Oct. - 1 Nov.
-4105000
Rough pump connected
Beam scrubbing

10-6

3000

10-7

2000

increase of the base pressure
10-81000
Leak Test

10-9
10/31/2002
9:00:00

10/31/2002
15:00:00

But there was
no improvement.

400010/31/2002
21:00:00
time

11/1/2002
3:00:00

011/1/2002
9:00:00

Beam Current [mA]

Pressure [Pa]10-5

Belle solenoid off
IP off
RGA onCCG_H01A
CCG_H02
CCG_H02A

CCG_H23
CCG_H23A
CCG_H24

Even after
NEG
conditioning,pressures did
not recover.

DCCT:HER
DCCT:LER

1-2 Nov.
-4

5000

10-5

4000

1010-6

3000

10-7

2000

10-8

NEG
Conditioning

10-9
11/1/2002
9:00:00

11/1/2002
15:00:00

Increase of the base pressure

11/1/2002
21:00:00
time

11/2/2002
3:00:00

1000

011/2/2002
9:00:00

Beam Current [mA]

Pressure [Pa]Still abnormal dynamic pressure

It wasdecided toinspect theinside of IPvacuum
chambers on 2Nov.

Inspection by CCD scope• Dark spots on Au plating of IP
chamber were found.
• But no other serious defects of
the inner surface of vacuum
chambers were not found.
• Without finding any measures,
we started pumping down of theIR in the afternoon of 4 Nov. andcontinued beam scrubbing till themorning of 7 Nov.

CCG_H01A

CCG_H23

CCG_H02

CCG_H23A

CCG_H02A

CCG_H24

DCCT:HER
DCCT:LER

10500010-5

400010-63000

10-7Beam scrubbing

10-8

10-9
11/5/2002
16:00:00

2000

1000

11/5/2002
22:00:00

11/6/2002
4:00:00
time

11/6/2002
10:00:00

011/6/2002
16:00:00

Beam Current [mA]

Pressure [Pa]5-6 Nov.
-4

CCG_H01A

CCG_H23

CCG_H02

CCG_H23A

CCG_H02A

CCG_H24

DCCT:HER
DCCT:LER

105000

10-5

4000

10-6

3000

10-7

Beam scrubbing
2000

10-8

10-9
11/6/2002
16:00:00

1000

11/6/2002
22:00:00

11/7/2002
4:00:00
time

11/7/2002
10:00:00

011/7/2002
16:00:00

Beam Current [mA]

Pressure [Pa]6-7 Nov.
-4

Final large Helium leak
• In the morning of 7 Nov., a large
amount of helium was seen on
the display of RGA.
• By changing a helium supply for
the IP chamber to argon and thento nitrogen, it was confirmed thatthe leakage is from the IPchamber.

Trend of the residual gas from 6 Nov. to 7 Nov.
2

16

28

H-Cur

4(He)

18

32

L-Cur

Residual Gas 6-7 Nov. (at H23A)
105

5000

10000

4000

1000

3000

100

2000

1010001
11/6/2002
16:00:00

11/6/2002
22:00:00

11/7/2002
4:00:00
time

11/7/2002
10:00:00

0
11/7/2002
16:00:00

Beam Current [mA]

Peak Height (Arb. unit)

HeFinal Remark•Now it is confirmed that the leakage is from the beryllium part of theIP chamber.
•The first symptom of the leakage was an abnormal outgassing around
IP. The main component of the outgassing was hydrogen gas according to
the experience during the leak test on 31 Oct. The outgassing rate wasroughly 10-6 Torr l sec-1.
•Though helium was observed in the residual gas, the partial pressure
was negligibly small.
•Obviously the heat cycle due to the beam contributed to develop theleak.
•The final leak rate of helium was 2¥10-4 Torr l sec-1

END