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

DESIGN OF THE PRODUCTION TARGET FOR SLOW EXTRACTION
BEAM LINES AT K-HALL
Y. Yamanoi, M. Sekimoto, M. Minakawa, E. Kusano, K. Agari,Y. Sato, Y. Suzuki, M. Takasaki, J. Imazato, M. Aoki*, T. Fukudat
KEK, High Energy Accelerator Research Organization,
1-1 Oho, Tsukuba, Ibaraki, 305-0801 Japan

Abstract
This paper reports the design of a secondary particle
production target used in counter experimental hall atJHF. The primary protons of 3xl0 14ppp accelerated by
50GeV are transported to this experimental hall. Theproduction target used in this hall is made from a nickel,
and has a cylindrical shape with a diameter of 240mm in
54mm in sum total thickness. The disk of one sheet is
6mm in thickness, and piles up a total of nine sheets witha lmm space. In order to reduce the incidence proton· density in the target, this target is rotating in 60 rpm byusing the air bearing. Therefore the proton density can beseemingly lowered even to lxiO"ppp, and the generationof heat up can also be controlled. The production target
and its axis of rotation is force cooled with circulated
water in 200 litters. It will operate for annual 4000 hours,
and the amount of radioactive decay of Tritium will· beestimated about lOOBq Icc.

1. INTRODUCTION
The High Energy Accelerator Research Organization(KEK) and the Japan Atomic Energy Research Institute(JAERI) will jointly constructed the High Intensity
Proton Accelerator Facility (JHF) in Tokai, Japan [1].
The counter experimental hall called the K-hall fornuclear physics and high-energy particle physics in thisaccelerator facility is planned. The primary proton beamis accelerated to 50GeV and is taken out to K-hall as
slow extraction mode. This K-hall has been designed tohandle primary proton beam of up to 3xl0 14 ppp (protonsper pulse). The power of the primary beam in the K-hall
will be 750 kW; it is about 40 times greater than thecurrent design of the north counter hall at KEK 12GeV
PS. Therefore it is necessary to develop new technology
for handling high intensity beams. Especially theproduction target has the dirtiest conditions and designed
the accelerator and the nuclear institution to reference.

T1 Target are shown in Table 1.
Table 1· Incident Beam Parameters
Proton kinetic energy
50GeV
Proton beam current
15 fl.A
Number of particles
3x10 14 ppp
50GeV ring cycle
3.27 sec
Slow extraction pluse duration
0.7 sec
Beam size on T 1 target-ct>6mm

2. 2 General Layout
The floor layout of the K-Hall where T1 target is
assigned in Fig. 1 is shown. The T1 target for supplying
n , K mesons and p-bar to the secondary beam line
called Kl.8 is flrst built in K-Hall. The T1 target .area isone of the places where a radiation level is the highest ina primary beam line. As a pillar supporting a target's
own cover on up the heavy ceilings, the wall of the shapeof a thick chimney of iron or concrete is covered overaround a target. According to the formula of Moyer [2],the thickness of this ceiling cover is 2.5m of iron, and5.5m of concretes.
Primary Beamfl,··

Jofd~~-:/

i4!r:·'························································F-:v

Figure 1: The floor plan of the K-Hall and T1 target

2. DESIGN CONSIDERATION

2.1Incident Beam Parameters

The important parameters of the primary beam thatcarries out incidence to the production target called the*Present address: Osaka University, Osaka 567 Japan
tpresent address: Osaka Electro-Communication University, Osaka,
572-8530 JapanThe 40t main crane and 20t sub crane are provided inthe ceiling so that maintenance and installation can be
performed distantly.

2.3 Target Design General Requirements
This T1 target and its equipment must fulfll thefollowing conditions in respect of operation of a beamline.

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

I.

The rate of loss of the primary beam allowedfrom the viewpoint of radiation management here
should be a maximum of 30% or less.
2. Make into the maximum the amount ofgeneration of the' secondary particle used for anexperiment in this beam loss limit.
3. It is the size and shape that consider of the optics
of a secondary beam line, and can be regarded ina point-like source.
4. A lifetime of the target itself and its equipment
should be more than for at least one year. The
operation time with which a physics experimentcan be presented is planned as 4000 hours/yearby the maximum.
5. Perform installation, withdrawal, and temporary
evacuation in remoteness and a short time. The.production target, which is most radioactive inorder that making it evacuate temporarily for
maintenance work, such as a surrounding
electromagnets or these equipments, may reduce
unnecessary contamination of a maintenanceworker.
The T1 production target at the K-Hall was designed
based on the above matter.

3. A FIXED SOLID TARGET AND ITSPROBLEMS

3.1 Solid Target
Extension of the present fixed solid target has been
considered from maintenance and the viewpoint of beamtargeting at the beginning of a· target design. The
temperature distribution of heat up in the target by theincidence proton beam is estimated by calculating forenergy deposition using the code name CASIM. With thehigh-density material (e.g. platinum, tungsten) currently
used, it is clear that a problem is in the diffusion speed ofheat in the target volume. Since the heat in a target
material diffuses at acoustic velocity mostly, it is verydifficult to suppress the temperature rise by the heat,
which occurs in the small volume by the high intensity
beam.
For example, the tungsten metal of high melting point3387"C was used as the target material, the inside of atarget amounts to a maximum of 1400°C with the beamof the pulse at a few pulses. If the heat removal is able toattain smoothly, that is a heat transfer coefficient isassumed to realize in 1000 W · m-2 • K' ,and the basetemperature of the target is became under 300°C. In
this case, a difference between top and base temperature
will be too large and will start the metal fatigue by heatstress. We wants to bring cooling water close to an heatup volume in order to cool as much as possible, but thet~mperature on t.!Ie. target surf~ce, which touche,s .acooling water is over the it's boiling ppint of atmosphencpressure by this simulation.

3.2 Solid Target Design Criteria
In order for a coolant to perform heat removal for asolid target compulsorily, the target material itself musthave the following conditions taken into consideration.
1. The temperature in a solid target must not exceed
the melting point and a brittle changes
temperature, which a material has.
2. The heat stress produced by an energy depositionor the difference of a heat up down is made not toexceed the permission yield strength of a target
material.
3. It is made for the solid surface temperature, which
touches cooling water not to reach a boiling pointof a coolant.
4. The heat flux on the surface of a solid should notexceed marginal heat flux that a material has .
5. Take into consideration the influence by corrosivegas or radiation irradiation.

4. ROTATING DISK TARGET

4.1 Target Materials
The material of the production target referred to thetarget design study of the g-2 group at AGS [3] that is
experimenting using up to 6xl0 13 protons with 30GeV
and the FNAL antiproton source [4]. Although bothtargets were fast extraction mode, it is important that thenumber of incidence particles is high-density on a target.
The most important parameters of the target material
itself are a latent heat of fusion, yield strength, heatdiffusion coefficient, thermal diffusivity and a pressureof the .internal shock stress by generation of local heat up.
The value of a shock pressure in adiabatic change isgiven from the state equation of Mie-Gruneisen [5].
These representation values of the materials that serves
as some target candidates are shown in Table 2.
Furthermore, it decided to adopt nickel or a still stronger
nickel alloy in consideration of the corrosive one-proof
by cooling water and a NOx gas.
Table2· Target Materials
TargetMaterialLatent
Heat ofFusion
JigPtw
CuNiFe101192
205
292
272

YieldStrength
MPa

Thermaldiffusivity
m2/s

Shock
pressure
Pa·kg/J

18555054/270150/480
120-150

25 k
67k
116 k
23 k
23 k

56.0k
31.6 k
18.3 k
15.9 k
13.9k*Material condition: soft/hard

4.2 Heat and Thermal Stress Problems
When using a production target as nickel with thedensity 8.9g/cm3 and an interactionlength A. are, 14.91cm,
it makes the rate of beam loss 30%, therefore themaximum target length is 5.3lcm. The target has theshape of a cylinder with a diameter of 240mm in 54mm-394-The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

in sum total thickness. The disk of one sheet is 6mm inthickness, and piles up a total of nine sheets with a 1mmspace. The reason for having sliced the disk in thedirection of a beam axis is for dividing the stress of theshock wave that is spread in the advance direction of abeam. In order to make the path of a heat longer and tolower the temperature of the axis of rotation, there is acut of a spiral in a disk. A drawing of one target sheet isshown in Fig.2.
According to the cascade simulation, it is the last diskthat energy deposition becomes the maximum with a
110MeV · cm-3 per one proton on a beam axis. The
distribution of the energy deposition by one proton on adisk is shown in Fig. 3. The amount of energy deposition
increases almost linearly in this thickness.

t f
T able3 : Compartson wi"th a the fi xe d and aroamgstae
Fixed
Rotating
3xlOI4ppp
lxl0 11 ppp
Incident beam density
Target cross section ofWidth6mm
c/!6mmheat upLength 506mm
5.28 kJ/cmj
Energy deposition
104 J/cm3Max. Heat-up perl344K
25.4K
pulse**One pulse is a 3x10 14protons in 0.7 sec duration.

4.3 Beam Window
In order that contamination of the nitrogen oxide andozone gas generated in a target chamber, a target
chamber must have air tightness and the closed
circulatory system must be made. Therefore we thinkthat the beam window of an aluminium alloy thin foilwith 80 Jl m thickness in 1OOmm diameter by grinding
machining, or a zirconium ceramics (3mol%Y20rZr02)
with 30 Jl m thickness in 60 mm diameter will be adopted
as this partition.

4.4 Cooling Water
The production target is force cooled with circulated
water in 200 litters. It will operate for annual 4000 hours,
and the amount of radioactive decay of Tritium will be
estimated about 100Bq /cc.

Figure 2: A drawing of one target sheet

S.SUMMARY

0.18
0.16

r=O em

0.14'f? 0.12
E

We designed the rotating disk target by a nickel for theK1.8 beam line. The distribution of energy distribution
and temperature was estimated on the target, it ispossible to remove heat by making it rotate, and it proves
out that there is the manufacture possibility as a solidtarget.

•••••• ••••• •• •~ 0.10::;; 0.08

8w 0.06
0,04

6. ACKNOWLEDGMENT

0.02

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).

0.00
02468101214Beam Depth [em]Figure 3: The distribution of the energy deposition

REFERENCES

The method of making rotate a target and lowering thebeam incidence density per place was adopted. Therefore
the incident beam density can be seemingly made small
to about 1150 by rotating per minute 60 times. The
incident Beam density and the highest temperature in thedisk are in fix/rotation state is shown in Table 3. The
incident beam is applied to a 1Omm place from the edgeof a disk. The heat by incident beams can be directly
removed from the disk target surface by this method.
Since the temperature rise became small, a heat stresshardly becomes · a problem. Rather the cooling of atemperature rise with the axis of rotation and the airtightcontainer supporting a disk is a problem.

1.

2.

3.
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5.

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