STATUS OF THE MAINTENANCE FOR THE KEK 12GEV-PS MAIN RING
AND POWER SUPPLY
Hikaru Sato, Susumu Igarashi, Katsumi Marutsuka, Katsuhiko Mikawa, Masashi Shirakata,
Tsuyoshi Sueno and Noboru Tokuda
KEK
More than 30years passed since the KEK 12GeV-PS
construction, some of accelerator equipments are highly
radiated, especially the injection and the extraction
equipments. In recent years, the higher intensity beam has
been required for such as the long baseline neutrino
oscillation experiment and rare decay experiments. Then,the circumference of the maintenance work has become
severe. Further, almost equipments of main ring andpower supply have deteriorated. Status of theMaintenance for the KEK 12GeV-PS main ring andpower supply are presented.

Neutrino Beam LineN

Abstract

North
Counter
Hall

EP2

East
Counter
Hall

EP1

Main
Ring

Linac
NML

Booster

1 OVERVIEW OF THE 12 GEV PROTONSYNCHROTRON ACCELERATORCOMPLEXThe 12 GeV Proton Synchrotron (PS) accelerator
complex comprises two 750 keV H-ion sources, the 40
MeV Linac, the 500 MeV Booster Sychrotron, and the 12
GeV Proton Synchrotron. The 12 GeV Proton
Synchrotron, which is called the Main Ring, supplies
proton beams to the long base-line neutrino oscillation
experiment (K2K), on which most of our effect is focused,
and to two slow-extraction lines (EP1 and EP2) for
various physics experiments. The Booster not only
operates as the injector to the Main Ring, but also
supplies proton beams to the Neutron Science Laboratory
and the Meson Science Laboratory (NML). The beampulse rate of the Booster is 20 Hz, while the cycle time of
the Main Ring is variable from 2.2 to 4 sec, depending on
the physics experiments. Only nine of the beam pulses the
Booster can afford to supply are injected to the Main Ringin a cycle time, and the remaining pulses are supplied to
the NML.
Machine layout of the PS complex is shown in Fig.1
and the basic parameters of the booster and main ring areshown in Table1 and 2, respectively.
Table 1: Parameter of the 500 MeV Booster
Circumference :37.699m
Injection Energy :40MeV
Extraction Energy :500MeV
Number of Period=8 (Combined Function)
RF :2Mhz to 6MHz
Harmonic Number :1
Repetition :20Hz
νH=2.2νV=2.3Pre-injector

Fig.1 : Machine layout of the PS complex.

Table 2: Parameter of the 12 GeV Main Ring
Circumference :339.29m
Injection Energy :500MeV
Extraction Energy :12GeV
Number of Superperiods=4
Number of Period=28 (Separated Function)
νH=7.1
νV=5.2, 6.2, 7.2
γt=6.76
RF :6MHz to 8MHz
Harmonic Number :9
Repetition :2.2s – 4sNominal Intensity : 2-4×1012PPP (slow extraction)
6-7×1012PPP (fast extraction for K2K)

2 OPERATING STATUS
For recent few years, the Main Ring supplied proton
beams almost according to schedule without any serious
failure. PS is operated continuously except a long shut
down in summer (about two months) and twice short shut
down in a golden week (from end of April to early May)and the end of year to new year holiday. The Main Ring
supplied protons to the slow-extraction line EP1 and EP2
for a proton of operation time. Almost three quarters ofoperation time is dedicated to the fast-extraction line EP1
for the K2K experiment. Run was conducted to supply
sometimes the two slow-extraction lines EP1 and EP2
simultaneously. The number of protons in the neutrino
production target of K2K accumulated during FY2000 is2×1019 and the total number accumulated so far has
exceeded 4×1019 , which is 40% of the target value of theK2K experiment.
An operating time in FY2000 and FY2001 are shown in
Table 3. The experimental time for high-energy physics
amounts to 4,141 hours. It accounts for 79% of the total
operating time of 5,715 hours. The beam untilization time
for the NML, most of which is shared with the 12 GeV
Proton Synchrotron users, is more than 5,000 hours,
accounting for 88% of the total Booster operation time.
In FY2001, the beam intensity of the Main Ring washeld at the level required by the K2K experiment; i.e.,
about 7×1012 protons per pulse measured at the end ofacceleration. This value of beam intensity was alreadyachieved at the beginning of FY1999 after a series ofmachine development steps. The history of the average
beam intensity of the Main Ring is shown in Fig. 2. For
slow-extraction operation, however, the beam intensity islimited by the radiation hazard near the extraction section,
which appears in Fig. 2 as lower intensities in the latter
half of FY2001. The beam loss has increased with theintensity upgrade, then the residual activation was gettinghigh level as shown in Fig.3.
Total operation time was more than 4500 hours per year
for a recent few years, and 70-77% time was dedicated tophysics experiment and about 15% was used for theaccelerator study and tuning. The accelerator was
operated in fairly good condition with less than 5%
machine failure. However, the maintenance should be
reduced due to the cut down of expenditures and every
body anxious for the troubles of decrepit since PS is so
old machine.

occurred at the commissioning for K2K experiment in1999.

Fig.3 : Residual Radiation Level in the Main Ring

Fast Extraction

12

8x10 ppp

Slow Extraction
7x1012ppp

Table 3: Operating time in FY2000(upper)and 2001(lower)

12

6x10 ppp

12GeV PS
hours %

12

5x10 ppp

12

Total

4x10 ppp

3x1012ppp

Accelerator tuning

12

2x10 ppp

Accelerator studies

12

1x10 ppp

12

0x10 ppp 79

80

81 82

83 84 85 86

87

88 89 90 91 92 93 94 95 96 97 98 99 00 01 02

FISCAL YEAR

Fig.2 : History of the average beam intensityof the Main Ring.

Beam utilization
System down
Accelerator failure

Accelerator failure in FY 2000 and 2001 aresummarized in Table 4. Rate of failure time is less than
5%, but in FY1999 the failure time was 450 hours(7%).
We had no extra budget to construct the fast extraction
system at EP1 for K2K experiment, but the maintenancebudget had been cut almost 1/3 for three years, 1996-1998.
Then, the several sever break down of equipment , had

NML
hours %

5235.3 100 5714.8 100
100 5877.3 100
267.7 5.1 148.5 2.6
212.3 4.1 154.5 2.6
374.2 7.1 226.3 4.0
221.2 3.8 221.2 3.8
4141.6 79.2 226.3 4.0
4214.5 80.6 5062.8 86.1
451.8 8.6 306.6 5.4
583.3 11.5 438.8 7.5
289.8 5.5 174.2 4.1
278.1 5.3 239.4 4.1

Table 4: Accelerator failures in FY2000 and 2001
FY2000FY2001minutes number minutes number
ofof
failurefailure1.Pre-Injector
118
9
624
22
2.Linac2697
226 2544130
3.40 BT
662
109 8358
81
4.Booster MAG
887
10
354
12
5.Booster RF
737
6
30
6
6.500 BT
1434
23
162
20
7.Main Ring MAG
0
0
918
8
8.Main Ring PS
3457
4
126
4
9.Main Ring RF
3657
23
666
22
10.Extraction1554
31 229218
11.Control
38
6
612
25
12.Monitors
139
1
0
0
13.Vacuum (B+M)
2005
1
0
0
14.Human error
51
10
48
14
15.Others
60
3
6
2
Total
17496
462 16740
364

3 PERSONNEL ORGANIZATIONSYSTEM
The total number of the KEK staff is 733, consisting of
380 Research Scientist, 196 Technical Engineering Staff
and 129 Administrative Staff. Usual Personnel
Organization depends on the needs of equipment
maintenance number of staff in accelerator department is
127 Research Scientist, 60 Technical Engineer and 5
administrator. PS group (36 staffs) is belonging to the
Accelerator Division IV and comprises nine teams, PreInjector, Linac, Booster Ring and Beam Transport, Main
Ring and Extraction, Accelerating RF for Booster andMain Ring, Control and Beam Monitoring, Vacuum
System and Beam Handling. Table 5 shows a personalorganization of PS division in 2003 and 1998. Situation of
the research scientist is organized like University system.
Number of persons reduced for five years, although themaintenance work and operation have become severe
condition.

4 HOW IS MAINTENANCE AND
OPERATION ORGANIZATION ANDPERFORMANCE
Maintenance staff and Operating staff are not divided
clearly. All of staff have the maintenance and machine
operation duty. Five staffs in accelerator division 1 , who
dedicate to work for the High Intensity Hadron Project,

cooperate us for machine operation as shown in Table 4.
Usual operation cycle was 16 days operation and fivedays scheduled maintenance at the WAO 1998[1]. First
two days were used for machine tuning and several shifts
were utilized for the beam study. We have to work for thestarting up of beam tuning and also repeat a machine
operation shift as two to three times in one operation
cycle. After starting the K2K experiment, an operation
cycle extended to two or three months continuously
including two days of the conditioning for the pre-injector
should be scheduled for every three weeks.
Staff can not become to expert for the every part ofmachine operation and maintenance except for one's duty,
so the operating shift staff and beam handling group ask
for the maintenance group to tune the corresponding partof machine. If tuning work continue to after five or till
midnight, it should be a volunteer work.
We did the simple and easy maintenance during theshort shut down (five days including the week end) as aformer case. For the case of the severe break down, thechief of beam handling group should decide to change themachine operation schedule and order to the maintenancegroup to fix it. Shift leader can also decide in stead of thechief of beam handling group. If the trouble is so hard tocontinue the machine operation for a long time, thedirector of PS division have to decide the managing of
fixing and re-start schedule.
At this present, unscheduled maintenance is main rule
for minor troubles but heavy maintenance is scheduled in
the summer shut down.
Several months shut down period is scheduled for every
summer, but it is reduced to two months recently
according to the user request. All of us would like toescape the work during a golden week and the new year
holiday week, but the staffs of the group, which has theequipment to fix until machine start up, have to work hardwith giving up their vacation and it is also a volunteer
work.
We try to find the cause of break down and to change
the break part to the spare if we have. In the case of nostock and/or the trouble of unknown reason, we order to a
maker. We contract the emergency call with the importantmaker. We have no trouble shooting guides andprocedures, it depends on the artificial technique of theexpert, but the beam handling group is under processing
to do it.
If the radio-activation of the break down equipment is
too high to fix it by it's maintenance group only for theactivation protection. Beam handling group arrange to ask
the help to another staff in according to the order list
which is made by some formula consists of individual age
and radiation exposure amount[2]. This list is maintainedby the beam handling group to averaging the activationlevel for all of the staff under some correction equation.

Table 5: Personal Organization at the PS division
19(27) Research Scientist
17(19) Technical Engineer
36(46) Total( ) number at WAO1998
PreInjector

Linac

Booster Main Ring
&Beam&
Transport Extraction
1
1RFProfessor

01

Assistant
Professor

0

0
(1)

1

1

1

Research
Assistant

1

0
(3)

1
(3)

2

1
(2)

3
(2)

1

1
(2)

1

Technical
Engineer

2
(3)

3
(4)

3

3

1

3

2

0

3

0

5 EXAMPLE OF THE MAINTENANCEFOR THE MAIN RING GROUP
Main ring group comprises two sub groups. Two expert
engineers and one research associate take care of the main
ring magnet power supply system. The others (oneassociate professor, one research associate and one
engineer) take care of the main ring magnet, thecorrection magnets and the equipment for the slow beam
extraction. We have been performed the periodical
maintenance once a year (every other years on every three
years depend on the items to save the budget) during
summer long shut down. A few days later from beam off,the officer at the radiation science center measure theresidual radiation level in the ring as shown in Fig.3[3].
We start the maintenance work at the lower radiation areaand do it a later half to reduce the expose rate.

Control Vacuum Beam
Helper For&
Handling Operation shift
Monitorfrom ACC.Div.1
0
0
3
0
(1)
0
0
0
1
(1)
(1)
(1)

Steering Magnet Power Supply
6, 8 pole Magnet Power Supply
Bump Magnets Power Supply- Insulation check of the magnets and power supplies.
- Cleaning of all of the equipment.
- Check the screwing bolts.
- Check the decrepit parts and repair or replace them if
it is necessary.
- Check the leakage of the cooling water.
- Check the interlock system.

5.1 Scheduled maintenance
Example 1: Power Supply System
Periodical maintenance of the power supply once a year
during summer long shut down. It is not preventive, but
only check. If weak or break point are noticed in theheavy equipment, repair work will be scheduled to next
year maintenance.
Comporment of the Main Ring Power Supply:
AC harmonic filter
DC passive filter
DC active filter
Main Power Supply System(Converter/Inverter, Transformer, Interlock etc.,)
Analog Control System
Computer Control System
Others:
Septum Magnet Power Supply

Fig.4: Top of the quadrupole magnet. Too many small
parts of cooling pipe.
Example 2: Cooling Water System of the Main Ring
Until several years ago, maintenance of the coolingwater system was unscheduled, but many troubles haveoccurred recently[4]. Then we changed this scheduled job.
The work at the highly radiation area should be to latter
half or quit by case. This is very difficult work to replacethe small parts of cooling system due to too many parts
and narrow working space as shown in Fig.4.
- Cleaning of the equipment such as flow switch, flow
meter, valves, tubes, etc.
- Check the screwing bolts.
- Check the decrepit parts and repair or replace them if
it is necessary.
- Check the leakage of the cooling water.
- Check the interlock system.

5.2 Unscheduled maintenance
When a machine stop due to some equipment breakdown, experimental user request to repair it as fast as
possible. The officer of radiation science center is notpolice then they suggest only to take care at themaintenance work. We negociate with user directy forthe repair work schedule.
Example 1: Water Leak at the Main Ring Quadrupole
Magnet.
Date & Time : 1999 Oct.4. 10:00 am.
Repair Work : 16:50 – 19:00 (2 hours) after 9 hours
cooling.
Worker (Total)
16
Main Ring Group3
Volunteer7
Out-sourcing
6
Total Expose
3.439mSv
Maximum Individual Expose 0.3mSv
Number of people exposed over than 0.27mSv 6
Place : Quadrupole magnet neighbour the extraction
septum at EP1, that is very high radiation area.
Experience Report: Curie Mats set on the Quadrupole Magnet and
Septum.
: Off the Interlock power supply: Remove the cover for insulation: Notice the impossible work to replace theO ring and short pipe.
: Try to tighter the bolt -> Reduce the water leak.
: Set the funnel under the pipe and hosing to thedrain.
: Pull away the curie mats.
: On the interlock power supply.
This is only first aid!!
-> Proper repair was scheduled to next summer longshut down.
Example 2 : Insulation break of the extraction septum .
Date & Time : 1999 Nov.9 14:15
Repair Work : Nov.9 14:15 – Nov.11 18:10 (52 hours)
Worker (Total) :42
Main Ring Group5
Volunteer29
Out-sourcing
8
Total Expose
9.619mSv
Maximum Individual Expose 0.37mSv
Number of people exposed over than 0.3mSv 14

Place : Extraction septum at EP1.
Experience Report: Nov.9 12:40, 1999 Beam loss increased at EP1
area.
: Septum power supplies were down.
: Notice the interlock of the insulation break.
: Radiation survey by the radiation safety control
group.
: Radiation level : 20 – 40 mSv/h.
: Notice the water leak from the septum.
: Identify the impossibility of repairing.
: No spare septum -> Transfer from the using
septum at EP2.
: Set the Curie mats near EP2: Remove the power cable.
: Remove the septum at EP1.
: Remove the septum at EP2 and transfer to EP1.
: Set the Curie mats at EP1.
: Alignment of the septum at EP1.
: Tighten the bolts.
: Re- Alignment of the septum at EP1.
: Set the power cable.
:Test Operation
Example 3 : Water leak at the extraction septum.
Date & Time : 2001 Oct.9 12:00
Repair Work : Oct.9 12:00 – Oct.10 17:30 (29.5
hours)
Worker (Total) :22
Main Ring Group5
Volunteer14
Out-sourcing
3
Total Expose
5.4mSvMaximum Individual Expose 0.3mSv
Number of people exposed over than 0.3mSv 11
Place : Extraction septum at EP1, that is very highradiation area.
Experience Report
Oct.9 :10:30 Mechanical Center informed to CCR thata lot of amount water leakd in the tunnel.
:12:00 Notice the water leak in the septum at
EP1.
:13:00 Survey the radiation level.
:15:00 – 16:30 Remove this septum.
:17:30 – 19:30 Move the spare septum in thetunnel from the storage
Set the power supply cable and cooling water pipe.
Oct.10 :9:30 – 12:00 Measure the insulation between
coil and core and Alignment
Fixed in to beam line.
:13:30
Excitation test
:17:30
Check the stopper bolts of coil.
Break down of the septum magnet was occuerd
concentrated in 1997-1999. This is depend on the life
time of original constructed septum, but also there havesome weak point in the design against the electro-magnet
force. Main ring operation cycle become 2.2s for the K2K
experiment, that is twice faster than former cycle, thenlife time became short. It was difficult to remove theseptum from the beam line, since original design was notconsidered hands on maintenance. This caused highly
exposure in maintenance works[2].
We re-considered the design to proof the electro
magnetic force at the new spare septum construction, andalso in order to remove the septum easily from the beamline, slide base was improved as shown in Fig.4.

Budget : Tight budget does not allow us to prepare thewhole of spare parts and maintenance. Especially, themaintenance budget was cut in order to make aconstruction fee for fast extraction system during three
years, 1996-1998. It recovered once, but has been
decreasing continuously and will become to zero at 2006,
since the PS will be shut down at the completion of the JPARC. Table 6 shows the minutes of the operation andbudget.
Equipments : Deterioration depend on old product and/or
radiation damage
Personnel : Old age persons (46 years old average)
How do you take advantage of times when the machine isdown unexpectedly? Maintenance work starts as fast as
possible and volunteers are mobilized and outsourcing
order under director.
How are decisions made when repairs are considered(committee, small group, individual, etc.)?
1) Considered in small group
2) Order to director for help of mobilization
Extra-budget : supported by Division head, Department
Director, Director General, and societis supported by
IPNS (Institute of Particle and Nuclear Studies).

Fig.4: Improved slide base to remove from the beam line.

6 WHERE ARE OUR MAJOR PROBLEMSWITH REGARDS TO MAINTENANCE
Spares : Depend on the Budget
Expertise : Almost is generalist but not expert.
Planning : Difficult to make a scheduled maintenance due
to tight operation schedule and budget
Radiation : Depend on the place but equipment breaks
occur frequently in high radiation area etc,

6 ACKNOWLEDGMENTS
We would like to express our gratitude to Mr.K.Okazaki
for his help collecting data.

7 REFERENCES[1] H.Sato et.al, WAO1998, Vancouver, May 1998, P48.
[2] T.Kawakubo and H.Sato, Presented in this workshop.
[3] T.Suzuki, Presented in this workshop.
[4] H.Sato et.al, PAC2001, Chicago, June 2001, P1426

Table 6: Minutes of the Operation and Budget

Booster
Intensity (E12)Main Ring
Intensity (E12)1)
PS
BudgetMR
Operation Time(hours)

1997
1.5

1998
1.5

1999
1.8

2000
1.8

2001
1.8

2002
2.1

3.0
Slow
84
54
4800

3.5
Slow
46
35
3900

6.0
Fast
74
115
6100

6.0
Fast
124
147
5800

3.5
Slow
100
131
5879

7.0
Fast
86
112
2)
5800

Notice: 1) Normalized by an average for three years before (1994-1996)
2) Plan in FY2002
3) Until end of December