JAERI-Conf 95-021

1p-1
Status of the KEK-PS Main Ring
Hikaru Sato
National Laboratory for High Energy Physics, KEK,Tsukuba-shi, Ibaraki-ken, JapanAbstract
The KEK-PS has been operated successfully toserve an intense proton beam for the past two decades.
To meet the need of new physics research, there areseveral objectives for the PS upgrade, such as, toincrease the proton intensity in the main ring, toaccelerate the various ions and then the multifunctional
operation of PS. Especially , an intensity upgrade iscoming to the urgent problem for the long baselineneutrino oscillation experimen t and the rare event
experiment. Machine study to make clear the machineparameters and to find the curing of the difficulty toincrease the beam intensity has been under going. In thisarticle, the brief history of KEK-PS, an operation status
and an upgrade subjects will be described.

slow extracted beam spill is 1.7-2.0 seconds. The spill
servo controller was improved as a consideration of thefrequency response analysis of the slow extraction
process using the measured beam transfer function andthe frequency response of the servo control devices. 7)
This contributed to reduce a spill fluctuation about 10-db
and the extracted beam spill efficiency is maintained
about 90%. However, the extracted beam spill has beensometimes getting an uncharacteristic frequency due toan incoming disturbance in the commercial AC line. 8)

1. Brief History and an Operation Status
The KEK-PS consists of four accelerato r
complex, 750KeV Cockcroft Walton pre-injecto r,
40MeV injector linac, SOOMeV booster synchrotron and12GeV main ring. Brief history of the KEK-PS isshown in Table 1. Counter experiment started on July,
1976 using the secondary beam from an internal target
and the fast extraction for bubble chamber experiment 1)
and the slow extraction at 12Gev 2) started on January
and November, 1977, respectively. Booster Synchrotron
Utilization Facility to utilize surplus 500MeV proton
beam started on October, 1980. In those days, beam
intensity at the booster extraction and in the main ringwere 6xi0 11 ppp and 2x10 12ppp, respectively. In orderto aim the intensity upgrade, booster injection system
was changed to H-injection one3 ) from former positive
ion multi-tum injection and the linac was subsequently
upgraded to 40MeV after the long shut down on 1984.
As the results of much effort, the beam intensity· wasincreased to 5.4x10 12ppp in the main ring on June 1989
and 2.4x1012ppp for BSF on May 1990. On the otherhand, a polarized proton beam acceleration (typically40% polarization at 3.5GeV) was performed during thosedays.4)
Newly second slow extraction line (EPl) andNorth Counter Hall were established on 19905) at theterminated bubble chamber experimental area besides theEP2 line for the East Counter Hall. Since then, the slow
beam is extracted to both counter halls independently.
Simultane ous extraction has been desired but thefeasibility study is still under progress. Figure 1 showsa layout of the KEK-PS complex.
Main ring power supply and equipment for theslow extraction had been upgraded6) at the same time of
the constructi on of EP1 line, then the main ring
operation cycle was elongated up to four seconds and theFigure 1. Layout of the KEK-PS Complex.
After successive operation of switching between
polarized proton beam acceleration for main ring andhigh intensity proton beam for BSF, research anddevelopm ent for effective use of PS have been
performed , such as deuteron and alpha beam
acceleratio n9 ) and also beam was extracted at variousenergies. Especially, newly developed septum-bumpinjection system, which is the magnet system available
for both negative ion charge exchange injection andpositive ion multi-turn injection. 10 ) This is very noble
system and contribute to avoid much troublesomechanging the injection system with a large scaleevacuating process.
Although the highest beam intensity in themain ring was upgraded to 5.4x10 12 ppp on 1989 andincreased to 5.95x10 12 ppp on November of 1994, we
do not find and fixed yet the machine parameters forreproduction of this condition and an average intensity
during operation has been still 3-4 x10 12 ppp.
For reliable acceleration of low intensity beamsuch as alpha beam and polarized beam, high sensitive
beam monitors are going to install in the booster and themain ring.
One of the most effective upgrades for stableacceleration of intense beam and ions is an improvementof rf system; 11 ) such as a voltage-controlled oscillator,-11-JAERI-Conf 95-021

phase detectors, function generators, feedback loops andso forth.
Total operation time was more than 4500 hours
per year for a recent few years, and 70-77% was dedicatedto physics experiment and about 15% was used foraccelerator study and tuning. The accelerator was operated
in fairly good condition with less than 5% machine
failure.

with dependence on the injection error made by injection
kicker and septum magnet for the horizontal plane and bysteering magnet in the transport line for the verticalplane. Data analysis is under consideration since there aresome problems to make sure the systematic errors oftwiss parameters and beam position monitors.
The usual operating point of PS main ring is ataround vx=7.12 and vy=7.25 and the average beam

Dam V_aperture_Overlap

intensity from the booster is 4-5 x 10 11 ppp. In order toavoid beam loss due to the space charge detuning for ahigh intensity beam, it should be select rather higher
operating point. However, a third order resonance, vx +2v y= 22, and fourth order resonances, particularly
4vy=29 and 2vx + 2vy= 29 seem to be obstacles. Afterthese resonances were corrected as established usingrather low intensity beam, high intensity beam, 1.3 x
10i 2 ppp, were injected from booster and measured thetune mapping of beam survival as shown in Figure 3.
There is no region where more than 70% of the beamsurvives. A fast beam loss is brought at around anoperating point with smaller tunes, on the other hand aslowly beam loss is brought at around an operating pointwith larger tunes. Further studies should be necessary tomake clear these effect and how to cure.
Summary of the spring studies, which includes
also some results at the studies performed before summer
shut down, will be reported soon in KEK Report.

2015I\~ ~-+- Seclion IllI-....,

5_section,-a- Seclion II--SeclionN

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0Q

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~vv

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Figure 2. Results of the local aperture survey using
local bump method. First and second cells are missing
bend ones.
2. Intensive Machine Study for the Main
Ring Intensity Upgrade
As described above, every effort to realize theupgrade of KEK-PS have been devoted. Booster
synchrotron accelerates 1-2 x 10 12 ppp for Booster
Synchrotron Facility. If the main ring can accept andaccelerates the beam of this intensity with no beam loss,
10 13 ppp beams could be expected for main ring utility.
However, the circulating beam intensity is limited toabout 6 x 1012 ppp for some reasons which is not still
understood. An intensive machine study has been
performed to make clear the machine parameters and tofind the cause and curing of the difficulty in order torealize the beam intensity upgrade.
First of all, several tools for the machine study
were developed, such as an upgraded injection error
monitor, a fast beam loss monitor which can observe itturn by turn using computer workstations and soforth. 12)
After several times brain storming, the aim of
the first study was decided to concentrate the main ring
beam injection problem. The local aperture
measurements of the main ring were performed to makeclear the real orbit center in the vacuum chamber using asmall size beam scraped in the booster synchrotron. The
twenty eight steering dipoles were excited independently
to make a local bump orbit at each section in the mainring. The vertical aperture seems to be detennined by thediameter of the vacuum chamber in the bending magnet
as shown in Figure 2.
The orbit was set to the center of the vacuum
chamber as decided above, then the beam survival weremeasured to make clear and maximize the acceptance

8 o.3

0.1

0.1

0.2

0.3

0.4

Qx

Figure 3. Tune mapping of the beam survival injected
the intensity of 1.3 x 10 12 ppp from booster. Intensity
ratio of the beam survival until 350ms after injection tothat from the booster.
3. Design status for the fast extraction
systemFast extraction had been operated until July,
1981, for the bubble chamber experiment as a shaving
extraction. I) At this time, full beam which is circulatingin the main ring, should be extracted instantaneously forthe neutrino oscillation experiment. Then, several
research and development have been done.
-12-JAERI-Conf 95-021

Construction of 12.5Q kicker magnet andBlumlein system are advantage from the view point ofeconomy and saving the space of magnet setting.
Prototype one has just constructed and is facing on theexciting test.
Orbit analysis for the feasibility using existingslow extraction devices, such as bump and septum
magnets system is under consideration. This is important
for the switching the fast extraction and the slow
extraction for multi user request. We are considering now
the changeable system of the extraction kicker andelectro-static septum in the vacuum chamber. A large
orbit excursion is the problem since the extracted beam
passes through non linear magnetic field region of bothbending and quadrupole magnets. In order to constructeconomically, reconstruction of these magnets should beavoided. Detailed analysis of the magnetic field and orbit
calculation using this data are under going.
4. Summary
Acceleration of 5.95xl0 12 ppp intense beam
has achieved, however, an average intensity during
normal operation has been still 3-4 xlo12 ppp.
Although the spring studies were concentrated tothe problem during injection period, the reason of thebeam loss was not still understood yet . Further weshould make clear the problems at acceleration start andtransition crossing to realize the beam intensity upgrade.
Twenty years has passed since the KEK-PS
constructed, then several equipments and parts become
decrepit, then taking into consideration for this problem

is also important subject for the reliability of machine
operation.
The author would like to thank all of the PS
members for useful suggestions and discussions. He
thanks also to Beam Channel and Experimental Planning
Coordination members and users for theirencouragement.
References
1) J. McCARTHY and Y.Kimura KEK-74-16
2) K.Endo and C.Steinbach KEK-77-13
3) T.Kawakubo, Nucl.Instrum.& Methods, A265(1988)351
4) H.Sato et al., Nucl.Instrum.& Methods, A272(1988)617
5) K.H.Tanaka, Proc. of the workshop on Science at
the Kaon Factory, Vancouver, 1990, p.l6) H.Sato et al., Proc.of the 1991 IEEE Part. Accel.
Conf., 1991, p.908
Y.Shoji et al., KEK-93-107) H.Sato et al., 9th Sym. on Accel. Sci. & Tech.,
1993, p.376
T.Toyama et al., 9th Sym. on Accel. Sci. & Tech.,
1993, p.404 and to be presented in this Symposium8) H.Sato et al., Proceedings of the 1st Symposium onPower Supply Tech. for Ace.,
KEK Proceedings 95-3, p.60
9) Y.Mori et al., Proceedings of the 1993 IEEE Part.
Accel. Conf. , p.3754!.Sakai et al., Presented at the IEEE Part. Accel. Conf. ,Dallas,l995 and to be presented in this Symposium10) !.Sakai, Presented at the 14th Int.Conf.on Magnet
Tech., Tampere, Finland,1995
11) S.Ninomiya et al., KEK-93-4
12) M.Shirakata et al., to be presented at theICALEPCS 95, Chicago, Oct. 1985

Table 1. History of KEK Proton Synchrotron
Construction started1971
AprilPre-injector accelerated protons to 750 KeY
1974
June
Injector linac accelerated protons to 20 MeV
1974
AugustBooster synchrotron accelerated protons to 500 MeV
197 4
DecemberCommissioning of main ring operation
1975
December
Main ring accelerated protons to 8 GeV
19 7 6March
Main ring accelerated protons to 12 Ge V
19 7 6
December
Bubble chamber experiment started
1977
May
Beam intensity of booster was 6x10 11 ppp
1977
June
Counter experiments with slow extracted beam started
1977
NovemberBeam intensity of main ring was 2x10 12 ppp
1978
JulyExperiment with Booster Synchrotron Utilization Facility started
1980
JuneBabble chamber experiment was terminated
19 81
JulyPre-injector acceleration duct was renewed
1984
May[Long shut down during TRISTAN tunnel construction]
Booster injection system was changed to H- injection
1985
June
Linacupgradedto40M eV
1985
NovemberExperiment using polarized proton beam started
1987
May
Accelerator control was upgraded to MAP
1988
May
Beam intensity of main ring upgraded to 5.4xl0 12 ppp
1989
June
Beam intensity of booster upgraded to 2.4xl0 12 ppp
1990
May
Main ring power supply was upgraded1990
AugustCounter experiment at the North counter hall started
1991January
Deuteron beam was accelerated to 11.2 Ge V
1992
February
Experiment with deuteron beam started
1992
April
Septum-bump injection system was developed
1994
April
Alpha beam accelerated to 23 Ge V and experiment started
19 94
April
Realignment of the booster magnets
1994
August-13-