Safety
The 27th KEKB Accelerator Review Committee
2024.3.26
Toshihiro MimashiContents• Issues of radiation Safety• Radiation level on the Beam Transfer Line• Radiation level on Fuji and Tsukuba experimental hall
• Radiation level on Oho experimental hall (NLC in Oho
straight section)• ECS Cavity installation on Beam Transfer Line• Fire caused by power supplies• Personnel Protection System modification for tuningof injection beam (Fuji Mode)Radiation restriction Level• General area < 0.2μSv/h• Radiation monitoring area (KEK) < 1.5μSv/h• Radiation control area (Nuclear Regulatory Agency）< 20μSv/h

Radiation level measurement @ BT

Radiation level on the Beam Transfer LineElectron
Escape exit

Highest position
PositronRadiation Level above the Beam Transfer LineBeam

Repetion Rate # of Bunches

Beam Charge（1st Bunch)

Beam Charge（2nd Bunch)e-25Hz2 Bunch1.47nC

1.05nce+25Hz2 Bunch1.26nC

1.2nC

Radiation level in front of the most upstream BT escape exit is high
Before tuning: 0.8μSv/h (must be 0.2μSv/h or less)→Mainly it comes from electron beam
After tuning: 0.13μSv/h

Optical Fiber loss monitor

2024/3/25

軌道調整前後7

Screen Monitor inserted in the beam line
Radiation Level outside of tunnel becomes high->Repetition Rate is limited to 1 Hz
Average Repetion Rate < 0.3 Hz /HourH.Iwase

12.5Hz Beam Repetition Rate

H.IwaseRadiation level
on Fuji and Tsukuba experimental hall
General area < 0.2μSv/h

Radiation monitoring area(KEK)< 1.5μSv/h

Radiation level on Oho experimental hall
Non-Linear Collimator (NLC) is installed Oho straight section

Surround the beam pipe with 5cm of lead. (5m long)

Assumption of Simulation
Hit 1010 positron / s hits the collimator head

Y. SakakiTunnnel

Exprimental HallX axis

BeamX=0

Y. SakakiSurround the beam pipe with 5cm of lead 5m.
Surround the beam pipe with 5cm of lead + Stainless Steel(or polyethylene）11-13m.

Y. Sakaki

Y. Sakaki

Above portal shieldinside portal shield

Y. Sakaki

Big EffectReduce one order

Y. Sakaki

94 bunch
FC on
1 Hz
1 bunch injection

25Hz
2 Bunch injection(x 50 Radiation Level)

S.Terui

Open D06V1

Beam Current
2.6AS.TeruiECS Cavity installation on
Beam Transport Line TunnelM.YoshFire caused by power supply• MR Power Supply Fire (April 25th):• Occurred in a newly developed power supply.
• Incompatible parts (transformer) in the startup circuit (initial charge).
• The experience and knowledge that should be shared among J-PARC and KEK
accelerator personnel was not sufficiently utilized.

• Hadron Power Supply Fire (June 22nd):• The parts have deteriorated due to long-term use (manufactured in 1985).
• There was a blind spot in the inspection that was neither on the power supply
side nor on the load (magnet) side. => Polarity Changer• Not enough consideration was given to blind spots in inspection and thepossibility of deterioration due to thermal stress due to stable operation over along period of time.

MR Power Supply Fire (April 25th):
Occurred in transformer of a magnet power supply.

K.BesshoPolarity Changer

Voltage
Current

Output Voltage(V)Output Current (A)Increased resistance
Output Current decreased
Output Voltage increased to Maximum value (60V)

Contact resistance of Polarity Changer＜0.1mΩ → 90mΩIt caused 100kW power Loss

Trouble suddenly Occured
No signs could be observed

Policy at KEK• Polarity Changer• For power supplies that have the same type of polarizer that caught fire at J-PARC, remove
the polarizer or replace it with a more commonly used device.

• Confirm the status of periodic inspections of equipment.

• Equipment in operation that has not yet been inspected will be inspected immediately anda report will be made to the supervising engineer.
• Reconfirm that there are no blind spots or deteriorated parts.
• In areas subject to thermal stress, check for deterioration of components and loosening ofbolts.
• The status of fever will be confirmed using radiation thermometers, thermo-cameras, andpasting of thermo labels.

• When restarting stored old equipment, be sure to conduct a pre-use inspection.

As a continued response in the future• Power supply equipment related to accelerator operation shall be regularly
maintained and inspected by the manufacturer. For power supply units thatare approximately 40 years old or older and have not been regularly
maintained by the manufacturer, we recommend updating or replacing themso that they are not used for steady, continuous operation.
• Conduct cross-organizational reviews and confirmation work for newly
manufactured equipment.
• Consider improving the sophistication of interlocks that operate in theevent of a power failure.
• Network cameras will be gradually introduced as they will help detect
power failures early and help determine whether or not to enter a room inthe event of a fire.

1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
20022003
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
1120
12
20
1320
14
20
15
20
16
20
17
20
18
20
1920
20
20
21
20
22
20
23

0
0
0

0
0

450

50

2
4
17 16
8
60
3
1

35

0
0
0
10

11

350

100

1
8
13

150

4

138

43
37
3

1988
1989
1990
1991

14400

48
21
42
31
12
971
29131

1999

1998

691997

72

1996

74

1995

1020

1994

121993171992

913

1987

15

1986

78

1985

1984

1983

28

1982

134

1981

69

1980

0

1979

1

1977

500台

1978

0

1976

0台

1975

100台

1973

その他

600台

Tsukuba Campus manufactured
Before2000
531

400台

300台

200台

84
7

電源（東海 J-PARC）

Power Supplies in Tokai J-parc
3933003152502009511951 55 47029

Personnel Protection System modification fortuning of injection beam (Fuji Mode)• Issues of Injection beam tuning• Injection beam tuning with a beam dump inside the injector cannot be
performed for the e+ and e- beams at the same time.
• Requires polarity reversal of the electromagnet at the injector end• BT dump mode cannot be used while entering the KEKB main ring.

Personnel Protection System was modified to solve these problems

Beam Dump

Fuji mode
• The PPS was modified so that even if there are people in theTsukuba Area, a beam can be transfered all the way to BT End.

• Injection beam tuning is possible even during long-term
shutdown of Belle (LS1)• Even if there is tunnel access for Belle work or work in theaccelerator hardware group, the injection beam can be tuned
during the day.

Beam Shutter

Beam Shutter

図⾯：⽥中幹M.Tanaka

Fuji Mode AreaのPersonnel Key(Fuji,6C,9C)