The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Status of the 12-GeV KEK-PS Upgrade Project for the Long-BaseLine Neutrino
Oscillation Experiment
Hikaru SA TO and the Task Force TeamHigh Energy Accelerator Research Organization (KEK), Tsukuba, 305-0801, Japan
Abstract
Neutrino Beam Line

Commissioning of the long-baseline neutrino oscillation
experiments started from January, 1999, at the KEK-PS. In
order to prepare the experiment, intensity upgrade studies andthe hard ware improvements have been performed for a fewyears. The neutrino oscillation experiment requests the fastextraction. It needs to construct the fast kicker magnet system,and to re-construct the septum magnets and some otherequipment. The switching of the fast extraction and the slow
extraction can be done without the evacuation of theequipment in ord::r to serve the beam for the multi-users as
effective as possible. The results of the upgrad:: projects andthe commissioning will be presented.

NML

Pre-injector

1 Introduction
The KEK-PS complex comprises two 750 keY
Cockcroft-Walton pre-injectors, 40 MeV injector linac, 500
MeV booster synchrotron and 12 GeV main ring as shown in
Figure 1. It has been operated successfully to serve a proton
beam for more than past two d::cad::s [I]. Beams have been
serving by the half integer slow extraction to East and North
counter halls. Beam bunches accelerated in the booster except
to the main ring are utilized as NML (Neutron and Meson
Laboratory). To meet the need of new physics research, there
are several objectives for the PS upgrad::. Especially, anintensity upgrad:: is coming llo the urgent problem for thelong-baseline neutrino oscillation experiment[2]. Thisexperiment d::mands the fast extracted high-intensity beam
(1 0 211 protons at the production target for a few years) creates
the high current neutrino beam, which will be injected toSuper-Kamiokanoc, about 250 km west of KEK. The main
ring upgrade projects, intensity upgrade study, construction of
the fast extraction system have been performed [3, 4, 5, 6].
The neutrino beam line and the production target wereconstructed for same days by the beam channel group in theInstitute of Particle and Nuclear Studies [7]. Commissioning
has been done from January to the end ofJune, 1999, and thefirst event was d::tected on June 19 at the Super-Kamiokande[8].

2 Fast Extraction and Neutrino Production
Systems
Fast extraction of full circulating beam is requested forthe neutrino oscillation experiment. The EP I extraction
system was modified so that both of slow and fast extraction
are possible. The careful orbit analysis allows using existingslow extraction d::vices, such as bump and septum magnets
system, the changeable system of the extraction kicker andelectro-static septum (ESS) in the same vacuum chamber.

Figure 1 :Layout of the 12-GeV KEK-PS.
The kicker magnet consists of the 12.5 ohm kicker magnets
and Blumlein power supplies to save the transmission time[9]. The field strength is requested higher than 0.11 T and thisshould be realized within the space of3m in one long straightsection. The parameters of the kicker magnet are shown in
Table I and the issues of the modification are as follows,· ESS-kicker chamber construction, · kicker magnets
constmction, · ESS replacement, · septum A, B magnets
improvements,
septum C magnet power supply
construction, · septum E magnet replacement,· beam ducts replacement, · control system upgrade.
Table I . Parameters of the kicker magnet
Extraction Energy : 12GeV
Magnetic Field : 0. 11 T
Kick Angle : 5.0mrad
Gap (Vertical): 55mm
Gap (Horizontal) : 1 lOmm
PFN Voltage : 70kV
Rise Time (include transmission) : 155ns
Flatness : 1. 1J..LsA neutrino beam line extended from EP1-A primary beamline of the north counter hall towards the direction of theSuper-Kamiokande. This comprises the straight section, thearc section, the target station, the decay volume and the J..Lmonitor pit[7]. A fast-extracted proton beam will betransported about 400 m and focused onto a production target.
Two magnetic horns in the target station will focus produced
pions to the forward direction, so as to maximize the neutrino
flux which will be produced by decay-in-flight of pions in the
200 m decay volume. A primary proton beam will be stopped-10-

The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

in the beam dump. A high-energy part of muons will bemonitored at the !!-monitor pit. The neutrino flux is enhanced
by a factor of 14 when two magnetic horns are operated A
positioning of the Super-Kamiokande from the KEK site wasmade by the global positioning system (GPS) [10].

of instability and to measure the dynamic aperture are now
processing [15].
Since KEK-PS's impedance budget has been notconcerned, a lot of high impedance materials were periodicallylocated along the ring. The two-third of resonant impedance
devices, vacuum ducts between the bending magnet and thequadrupole magnet and the beam position monitor, werereplaced by low impedance ones in 1996[5]. Further, in orderto cross the transition energy in stable condition, y-jumpmagnet power supplies were upgraded to make the voltage
twice. The issues of the intensity upgrade are as follows,· realignment of the quadrupole magnets in the main ring,· replacement of bend-quad beam pipe, · upgrade of beam
position monitors, · installation of beam instrumentation, ·upgrade of the power supply for the y-jump magnets, ·installation of octu-pole magnets, · reliability of theaccelerating RF.

3 Upgrade Studies before 199 8
Every effort to realize the upgrade of KEK-PS have been
devoted Booster synchrotron accelerates more than 2 x 10 12
ppp for NML, however, the main ring cannot accept the beamof this intensity. Machine studies for the intensity upgrade
have continued to make clear the cause and cure of thedifficulty. First of all, several tools for the machine study weredeveloped andlor upgraded, such as an injection error
monitor[11], a fast beam loss-monitor, a tune measurement
system with an RF kicker, a fast wire scanner[12] and NMR
field monitor[13] for the main ring bending magnet.
The concentrated studies in the spring of 1995 was focusedon the beam injection to the main ring [3]. It seemed that theforth-order resonance was one candidate and in order tothe quadruple imperfection, several correction quadruples werenecessary. However there were no installation space in thering to install them, then the vertical tune was changed from
7.22 to 5.22 to reduce the effect of the fourth-order resonance.
In order to increase the vertical aperture, the re-alignment of themain ring magnet in the vertical plane was done during
summer shut down, 1996. The injection efficiency has
increased up to 95-97%. During the magnet realignment wasdone, the fast floor movement, which seemed to depend on theweather condition, was observed . In order to confirm thisphenomena, the measurement of the relative quadrupole
magnet level and the floor tilt in the ring were going on [ 14].
The edly current-induced sextupole field in the vacuum
pipe in the main bending magnets forces the horizontal
chromaticity into shifting from negative to positive values atthe beginning of acceleration. Then the instability occurs justafter acceleration starts. Octu-pole magnets were installed in
the main ring to suppress the head-tail instability by theLandau damping, and the studies to confirm the suppression

4 Intensity Upgrade Studies
at the Commis sioning

reduceMain ring beam tuning started on January 27 , 1999, by
the slow extraction mode and the neutrino beam line tuning
started on January 31 using slow-extracted beam. On themorning of February 3, the extraction system was changed
from the slow extraction mode to the fast extraction mode aftertuning the neutrino beam line except the horn system. Systemchange was done in only three hours and main ring beamtuning started again. The kicker magnets were excited and thefast extracted beam was observed on the monitor screen at theexit of the septum magnet E. After short beam-off for the
check of some instrumentation, the fast extraction tuning
started again and the beam was confirmed on the production
target. Fast extraction started again on March 3 after thecompletion of the hom system, and the task force tried torealize the beam intensity upgrade in the main ring[l6].
Fast (< msec), medium (< a few msec ), and slow loss(<50 msec ) at the injection porch strongly depend on a set ofbetatron tunes in both directions beyond a beam intensity of
6.0x10 11 /bunch. Fast loss is caused from betatronmismatching and rapid emittance blowup due to space-charge

Screen monitorb~~~a~cr=rl,:.Jv-=="1~~~- --- _cr_ ~ ~c05mFigure 2 : Layout of the EPl extraction system. ESS and kicker magnets are installed in
the same vacuum chamber.
Fast extracted beam bunches are measured by CT at the exit of septum magnet E.

-11-The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

forces coupled with the dynamic aperture d:pend on octupole
fields. At this moment, the octupole magnets excited by theDC power supply. In ord:r to optimize the octupole at theboth of dynamic aperture at the injection and the correction ofchromaticity after the acceleration start, the power supply
should be replaced to ac ones.
Most of collective instabilities depend on the local beamd:nsity. Bunch shaping by an artificial beam blowup in thelongitudinal direction is quite effective to cure theinstabilities. A modulation method of the RF voltage byband-limited white signals[l7] has been ad:lpted. A particle
resonates at one band of the modulation frequency and changes
its amplitude where the resonate frequency shifts due to a phasenonlinearity of the RF voltage, the particle then starts toresonate at another frequency in the same band. This resonant
dynamics continues until the particle arrives at the outerboundary that is covered with the band width. Although thecontrol of longitudinal beam emittance was not perfect, asubstantial reduction in the line d:nsity before transition has
been practically achieved and the acceleration efficiency wasclearly improved. This method was also adopted in the boosterand very effective to reduce the beam loss during main ring
injection. As a result, an average of 6.5x 10 12 ppp protons wereaccelerated. Figure 3 shows a history of the intensity upgrade.

[3]

[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]

5 Result[14]
Fast extraction was completed by the 12.5 ohm kicker
magnet with the Blumlein system. Fast and slow extraction
are easily changed in a few hours. Intensity upgrad: studies
contribute to realize the average of 6.5xl0 12 ppp protons(maximum 6.8x10 12 ppp) by the careful tuning of betatrontune, COD, the chromaticity control after accelerate by thesextupole magnets, Landau damping by the octu-pole magnet
and the RF voltage modulations in the both of booster andmain ring by the bunch shaping using a band-limited whitesignal. The first neutrino event was detected on June 19 at theSuper-Kamiokand:. For riwre intensity upgrad:, there aremany tasks should be requested such as re-alignment of both ofbending and quadrupole magnets, octupole power supplies
should be replaced ac ones, fixed system of the band-limited
white signal RF modulation, upgrare of the orbit correction
steering dipole magnet system and reliability of theaccelerating RF etc.

[15]
[16]
[17]

M. Sakuda, KEK Preprint 97-254, Feb., 1998
(Submitted to APCTP-WS)
Report on the 1995 Spring Machine Study at KEK 12
GeV Proton Synchrotron, KEK lnternal95-12 (inJapanese)
T. Toyama et al., Proc. of the 1997 Part. Accel. Con f.,
p.1599K. Takayama et al., Proc. of the 1997 Part. Accel.
Conf., p.1548
H. Sato et al., Proc. of the 1997 Part. Accel. Conf.,
p.1009M. leiri etal., Proc. of the 1st Asian Part. Accel. Con f.,
Tsukuba, Japan, 1998, p.579
http://neutrino.kek.jp/news/990628.1stSK/k2kreleasejp.html
T. Kawakubo et al., Proceedings of the 5th European
Particle Accelerator Conference, p.2441
H. Noumi et al., Uncle. Instrum. & Methods A 398(1997) 399
M. Shirakataetal., AIPConf. Proc. No. 315,1993,p.145
S. Igarashi et al., To be presented in this Symposium
H. Sato eta!., Presented at PAC 99.
http://ftp.pac99.bnl.gov/Papers/Wpac/THP166.pdf
H. Sato etal., Proc. of the 1st Asian Part. Accel. Conf.,
Tsukuba,Japan, 1998,p.263 ·T. Toyama eta!., Presented at PAC 99.
http :1/ftp. pac99. bnl.gov/Papers/Wpac/TUA31.pdf
K. Takayama, KEK Preprint 99-57
Toyama, KEK Preprint 99-38
To be presented in this Symposium

4x1012 ppp .... •••••••••••••••--••••••••••• .. ••••u•••••••••••••••••••••••••••• •••••• .. •••••••••••·••••••••••Acknowledgment
The authors would like to express their sincere thanks toM. Kihara, director general of accelerator laboratory and I.
Yamane, director of PS division, for their encouragement.
They are much ind:bted to many colleagues of PS and beam
channel staff for their discussions and collaborations.

2x10 12 ppp .................................. .................................. ............................... .

References[1][2]

Summary of Experimental Programs at the KEK-PS in
KEK-PS 1980's, 1990 and KEK-PS 1990-1994, 1994.
K. Nishikawa et al., KEK Preprint 93-55/INS Report297-93-9-FISCAL YEAR

Figure 3 : History of the accelerating beam intensity
in the main ring.

12-