The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

Design of Slow Extraction Beam Lineat 50-GeV PS in High Intensity Proton Accelerator Facility
K. AGARI, M. IEIRI, Y. KAKIGUCHI, Y. KATOH, M. MINAKAWA, T.MIURA, H. NOUMI,Y. SATO, S. SAWADA, Y. SUZUKI, M. TAKASAKI, K. H. TANAKA, andY. YAMANOIHigh Energy Accelerator Research Organization (KEK), Tsukuba, lbaraki 305-0801, Japan
3 GeV Syndwotron(P$)(..ooQ!n OriCUmference)

Abstract
A high intensity proton accelerator facility will bejointly constructed by High Energy Accelerator Research
Organization (KEK) and Japan Atomic Energy ResearchInstitute (JAERI) at the Tokai campus of JAERI. In thisproject, we are in charge of design, construction andoperation of the slow extraction beam (SEB) line at the50-GeV Proton Synchrotron. Since high power beam of750 kW will be transported through the SEB line, wewill deal with much heat and radiation which will begenerated in the SEB line. Therefore, we have toestablish the efficient cooling system and the tightradiation shield for elements in the beam line. In thispaper, schematic view of the radiation shield and a mockup of the SEB line are described.

50 GeV Syr.;hrotron(PS)H 50011 Crncumferenw)

Nuclear & Pan~Fadlity

Acceleralor-dnven
Tllili1Srtll)tation Syl;temExpe~imentlll Fa<:ility

Neutrino To
SUper-K!!IIliOkande~omFig.l: Layout of the accelerator complex [1]i'ul\lte

Extenllion=ro

1 INTRODUCTION
The present project aims to pursue frontier sciences inparticle physics, nuclear physics, materials science, life
science, and nuclear engineering with utilizing variety ofintense secondary beams such as muons, neutrons, kaons,pions, antiprotons, and neutrinos produced by highintensity proton beams. In the fields of nuclear andparticle physics, further developments of multistrangeness hypemuclear spectroscopy, CP violation of
the kaon decay, and long baseline neutorino oscillation
are expected by means of high intensity secondary beam.
The accelerator complex of this project consists of a
400-MeV proton linear accelerator, a 3-GeV rapid cycle
booster synchrotron, and a 50-GeV main synchrotron(50-GeV PS) as illustrated in Fig.l. The 50-GeV PSwould have cycle time of approximately 3.4 seconds with
0. 7 second of slow extraction period. The intensity ofthe extracted protons will reach 3.0X 1014 particles per
pulse (ppp), i.e. 15 f..l A, being the beam power of 750
kW [1].
Schematic view of the slow extracted beam (SEB)
lines from 50-GeV PS to the experimental hall (K-hall) is
shown in Fig.2. This facility is designed for the use of
intense pions, kaons, and other secondary particles. Two
primary beam lines (A and B) will be constructed. The Aline has three primary target stations, TO, Tl, and T2. A
thin target will be placed at TO to serve secondary beams
for test experiments. Thick targets will sit at Tl and T2
to produce intense secondary beams. Two secondary0IFig.2: Plan view ofthe SEB line and K-hall [1]beam channels, Kl.8 and 1tf..l, will be constructedfrom Tl. Another secondary beam channel, Kl.l, will
be connected to T2. The second primary beam line, B, isdesigned for the production of neutral kaon beam andother uses of the primary beam.

2 DESIGN CONCEPTThe important issues in the design of the present beamlines are to avoid or solve many problems expected to bearisen from heat deposit and radiation on the beam line
equipment induced by the high intensity beam. In orderto realize easy and safe maintenance, based on theexperience of the construction of North Counter Hall in
KEK 12 GeV PS [2], it is crucial to construct beam line
tunnels and service tunnels separately. Service tunnels
help easy access to beam line elements and are important
to maintain them for a long term.
Since people frequently access to the service tunnels,
those areas must be shielded to keep the residualradiation level reasonably low. We have to optimize theshape and thickness of the shielding materials withtaking easy maintenance into account.
It is also-464-

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

necessary to establish how to handle beam line magnets
and support systems, to align magnets, and to maintainthem as soon as possible. Therefore, we are building amock-up to simulate the 50-GeV primary beam line inthe East Counter Hall of the KEK 12-GeV PS.

3

COOLING AND SHEILDING

Since the power of the 50-GeV proton beam will reachmore than 100 times stronger than that of KEK 12-GeV
PS [3], special attentions should be paid for theconstruction of the new beam line in order to fulfil therequirements by ongoing environmental laws of radiation
safety, air pollution, and so on. The overall study ofradiation safety are made with considerations of the soil
activation and the radiation levels in K-hall, at theboundaries of facilities and site. The thickness of thebeam line shield is estimated based on Moyer's formulas,
as listed in Table 1 [4].
The losses of the primary proton beam at T1 and T2 areassumed to be at maximum 30 % of full beam intensity,respectively. Namely, it is expected that the beam powerof 225 kW would be released at Tl or T2. Therefore, theproduction target and peripheral · materials must bedesigned to handle such high power deposit. The
detailed description about the design of the target system
can be found elsewhere [5]. Large portion of thereleased energy is directly deposited to magnets, beampipes, shielding materials, and ·other beam line
instruments placed downstream of the target.
Particularly, the magnet, beam pipe, and collimator
located in the closest downstream of the target are foundto need the water cooling system. Detailed study isundergoing using the simulation code, MARS [6].
Since the beam line equipments near the production
target are highly activated by the beam irradiation, one
can never access close to them for maintenance. Whensuch a highly-activated magnet or other instrument isnecessary to be removed or replaced, we need to do it
remotely in principle. Electric power, cooling water,compressed air, monitor gases, signal lines, and vacuum
pipes to/from the beam line equipments have to be able
to be disconnected or connected at behind the radiation
shield, where the induced radiation level must be kept
reasonably low so that one can stay there to complete
such relatively-simple works. It is therefore vital tooptimize the configuration and the thickness of shielding
materials. The MARS code is employed also for thispurpose.

4 MOCK-UP OF THE BEAM LINEAs mentioned in Section 2, we are building a mock-up
in order to simulate the primary beam line tunnel,
particularly near to the production target. The plan andcross sectional views of the mock-up shield are shown inFig. 3.

Table 1· Shield thickness
Shield thickness [em]Position
Soil
IronConcrete
TO target upper

230

50

620

50
TO target lower
300
810
upper
50
split
Second310
50
Second split lower
370
100
K-hall upper
550
240
0
K-halllower
T1 target upper
250
550
200
200
T1 target lower
300
Beam dwnp upper
450
250
Beam dump lower
170
The mock-up shield is constructed with concrete blocks.
Iron plates are placed on the beam line tunnel floor, asindicated by hatched area in the figure. A beam-line
magnet will be installed on the iron plates. A trenchlying under the floor along the beam line is necessary inorder to circulate air in the beam line tunnel smoothly.
At first, we will install a dipole magnet, named
8D216MIC, in the mock-up. Fig.4 shows 8D216MIC.
The outer dimensions of this electromagnet is 1060 X 850
X 800 mm3• The weight is 6.1 ton. The magnet gap,pole width and pole length are 100 mm, 400 mm, and800 mm, respectively. The maximum current andvoltage are 3000 A and 33.1 V. The field strength of
1.4T can be generated. The coils of8D216MIC are usedmineral insulation cables (MIC). MIC is indispensable inhigh radiation environment.
Aluminium plates of 77 em thick in total are attachedon the top of the magnet so as to function as anotherradiation shield. When we install the magnet, the top of
the aluminium plate comes to the same level (height) of
the top of the present mock-up shield. Behind thealuminium shield, on the top of the mock-up shield, aservice area will be constructed. Maintenance works will
be done in the area. Thus, the thickness of thealuminium should be optimized depending on theradiation environment. If necessary, extra iron plates
will be inserted between the magnet and the aluminium
plates in order to increase the shielding power. The
upper part of the shield should be light material such asaluminium or concrete in order to reduce residual
radiation.
Manifolds for cooling water and bus bars for electric
power are placed above the aluminium shield. Crankedpaths through which the water pipes and conductors areconnected to the coils are made in the aluminium shieldwith keeping the shielding power.
Now, we are ready to install the magnet to the mockup shield. We will drive the magnet after the coolingwater, electric power, and other signal lines areconnected. Through this test drive, we will check if
unexpected problems take place. We will study many-465-

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

expected problems. For example, remote connection or
disconnection of the vacuum pipe has yet to be solved.
Iron p~te~r---r----~~

Ir----

beam line height can be adjusted in advance by inserting
proper spacers between the magnet and frame. However,re-measurement of the alignment of the beam-line
instruments and/or the pivots after many years of thebeam delivery may be possibly required. It should beconsidered how to realize. Ideas expected to resolvethese problems can be tested with this mock-up.

5 SUMMARY AND PROSPECT•Layout and basic specifications of SEB and target
stations in High Intensity Proton Accelerator
Facility were briefly introduced.
• Conceptual design of SEB was discussed andrequirements for the radiation shield, remote
maintenance and operation of the beam-line
equipments were summarised.
• Current status of the study for radiation protectionr---and cooling system based on various model
calculations
was reported. Further study for
LJt\Beam line
detailed design is under way.
• Actual configuration of a beam line magnet,shielding materials and peripheral devices wasF.L.
2500mmI
described in detail. Construction of the mock-up
will be completed by the end of November 2001,
Ire n nlate-,.
Beam line
Iand a test operation of the magnet will start soon.
F.L. 1200mm •. We expect to obtain a lot of experience through~IF.L. Omm
building up and operating a mock-up of beam line
magnet, and will be completely ready for the real
IIII
I
construction of SEB in the present project.
IFig.3: Plan(up) and cross sectional(lower) v1ews of themock-up shield
ACKNOWLEDGMENTS
Manifold
The authors wish to thank Mr. K. Kato of TOKIN
machinery Co., for his helpful advice in preparing themock-up. This work was partly supported by a Grant-in
Aid for Scientific Research (B), No. 11440084 and No.
12554009, of the Japan Ministry of Education, Culture,Sports, Science and Technology (Monbu-kagaku-sho).

~\,lJj

REFERENCES
Beam level(Side)(Front)Fig.4 8D216MIC
Alignment of the beam-line magnets and otherinstruments will be done with referring an array of pivots
along the beam line. The pivots are aligned and theirpositions are measured in advance. Then, a support
frame with holes to fit the pivots is prepared. Themagnet (or other beam-line instrument) and the support
frame can be fabricated so as to align the magnet center
to the holes before installation in the beam line. The[1] "The Joint Project for High-Intensity ProtonAccelerators", KEK Report 99-4 (1999).
[2] Y. YAMANOI et al., "Development of A HighIntensity Beam Handling System at KEK-PS New
Experimental Hall", KEK Preprint 89-165 (1989).
[3] K. H. Tanaka et al., NlM A363 (1995)114.
[4] S. Ban and H. Hirayama, "COMPARISON STUDYOF SHIELDING DESIGN METHOD FOR HIGHENERGY PROTONS", KEK Internal80-9 (1980).
[5] Y. YAMANOI et al., this volume.
[6] N.V. Mokhov, "The Mars Code System User'sGuide", Fermilab-FN-628 (1995). N.V. Mokhov, S.I.
Striganov, A. Van Ginneken, S.G. Mashnik, A.J. Sierk
and J. Ranft "MARS Code Developments", FermilabConf-98/379 (1998); LANL Report LA-UR-98-5716(1998); nucl-th/9812038 v2 16 Dec 1998. N.V. Mokhov,"MARS Code Developments, Benchmarking andApplications", Fermilab-Conf-00/066 (2000).

-466-