The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

DESIGN AND R&D STATUS OF NP-HALL BEAM DUMP IN J-PARC
K. Agari, M. Ieiri, Y. Katoh, E. Kusano, M. Minakawa, T.Miura, H. Noumi, Y. Sato,S. Sawada, Y. Suzuki, H. Takahashi, M. Takasaki, K. H. Tanaka, Y. Yamada and Y. Yamanoi
High Energy Accelerator Research Organization, 1-1, Oho, Tsukuba, Ibaraki, 305-0801, Japan
Abstract
Japan Proton Accelerator Research Complex (J-PARC)
is now under construction in Tokai-mura by the HighEnergy Accelerator Research Organization (KEK) and theJapan Atomic Energy Research Institute (JAERI). JPARC 50GeV-PS (Proton Synchrotron) aims to provide
more than 100 times higher beam power than that of KEK
12GeV-PS. An experimental hall for nuclear and particle
physics (NP-hall) [1] is designed to handle intense slowextraction proton beam and provide kaons, pions, andother secondary particles for multi-purpose physics use.
A beam dump at the aftermost of the primary beam line(A-line) is designed to safely absorb the 750 kW beampower. Its central core is made of copper and ironmaterial with water coolant, and covered by concrete forradiation protection. The beam dump has to be moved todownstream when NP-hall will be expanded in the future.
Important issues of the beam dump can be summarized asfollows.
1. Heat generation,
2. Radiation safety, and3. Moving safely to downstream in the future.
The present article reports the current status of our
R&D of robust and radiation-resistant cooling system andhow to move the beam dump safely.

1. INTRODUCTION
Fig. 1 illustrates the schematic layout of J-PARC. 50GeV-PS accelerates protons injected from 3 GeV-RCS(Rapid Cycle Synchrotron) up to 50 GeV, and extract
them to NP-hall in 0.7 sec duration. The slow-extraction
beam is transported through the beam-switching yard,
which is designed to separate the primary beam for thefuture extension. In NP-hall (fig. 2), beam hits theproduction target, which is made of rotating Nickel diskswith total thickness of 54 mm. [2] Through the target, theprimary beam is defocused to φ400 mm in diameter, andfinally absorbed by the beam dump.

T0T1beamdump

Fig. 2 Plan view of Switch Yard and NP-hallTable1 the parameter of proton beam
Beam energy
50 GeV
Beam power
750 kW
Beam pulse
3.42 sExtraction pulse
0.7 s
Number of particles
3.0x1014 ppp

2. STRUCTURE OF BEAM DUMP
The structure of the beam dump is shown in Fig. 3. The
core of this beam dump is made of Oxygen Free Copper(OFC), which has high thermal conductivity and radiation
hardness. The core part has a conical hollow(φ400x4000D), which is designed to comfort heatconcentration in the material. Iron and concrete shieldcover the dump core to keep the dose rate less than thelimit of soil-activation and spatial dose rate on the ground.
Cooling path of core part must be away from the centre ofbeam in order to minimize activation of the cooling water.

Service space
Concrete
FeCu

9.5m
9.5m

NP-hallProton beam

9m
6m

Fig. 3 Schematic view of beamdump

Fig. 1 Layout of the accelerator complex

Since the dump-core of OFC (3000x2000x5000mm3) is
too large to be made as a solid, it is comprised of 50
divisions (3000x1000x200mm3/part) in the beam
direction.
The number of division of the core must be minimized
to reduce thermal resistance in the gap of each block. Inaddition, we have to take the available size of OFC in
Japan into account to construct the beam dump.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

3. DEVELOPMENT OF COOLINGSYSTEM

Heat transfer rate is improved between pipe and platewith applying thermal spraying, and erosion andcorrosion can be ignored by using Stainless pipes.
However, the demerit is indirect cooling, and so heattransfer rate is lower than that by other ways describedbelow.
For investigating heat transfer rate of thermal spraying,
we carried out experiments as follows.
The experimental setup and condition is shown in Fig.
5 and Table2. In this case, we used only aluminium wire
spraying without brazing.
60

60

The dump core is designed to accept full power of 750
kW proton beam. In this section, the numerical analysis ofheat convection and the prototype of cooling system arediscussed in detail.

60

60

4- φ 10-+0.0 05

8The Service Space (S.S.) over the beam dump is used todo maintenance job of piping, thermocouple thermometer,vacuum, and so on. The S.S. is covered with concrete
shield to reduce the radiation exposure in the workspace.
Below the core there are two hollows(1000x1000x9000mm3) for shifter and rails, and wewould install them just before moving to downstream
between first and second phase.

50Numerical calculation
The energy deposition in Cu-core by the 50 GeV proton
beam was estimated with MARS code [3]. The size of theprimary beam at the entrance of the beam dump is φ400 indiameter, and heat production is calculated by assuming
the beam intensity to be 3x1014 proton per pulse (PPP) in
0.7 sec extraction period.
The heat propagation and convection was analysed bythe ANSYS program. Based on the calculated energy
deposit by MARS code, ANSYS program analysed heatpropagation in OFC-core with about 380W/m/K heat
conductivity. The heat convection from OFC to coolingwater is assumed to be 600 [W/m2/K] on the surface ofOFC-core. Fig.4 shows a typical result of heat analysis.
The maximum temperature is 264°C at z=3000mm.
OFC’s softening temperature is around 200°C, so theshape of conical hollow must be optimised to make theenergy deposit uniform, or increase heat transfer rate
higher than 600[W/m2/K]. To confirm the heat convection
from OFC to cooling water, we are testing three coolingschemes.
Proton beam
50GeV-15µA(750kW)φ 40cm

300

100

500

Fig. 5 experimental model
Table 2 experimental conditions of the cooling test
Type of thermal spraying
Aluminium wire
Maximum heat
~800W
Flow rate
5,10,15L/min
Flow velocity
0.9,1.9,2.8m/s
Reynolds number9900,19800,29800
As a result of this experiment, heat transfer rate
between OFC and water temperature were 950, 1110,
1260 [W/m2/K] for the water flow rate of 5, 10 and15[L/min], respectively. It is noticed that all the results
were more than 600 [W/m2/K], which is used in thecomputer simulation. As shown in Fig. 6, an air gap
between SUS pipe and OFC block was found afterthermal spraying. It would be possible that the heattransfer rate can be improved if the shape of copper blockand the method of thermal spraying are optimized.
Thermal spraying

Cu 5m
Fe 1mSUS pipe
Maximum temperature
260°C1mFig. 4 Result of thermal generation

Cooling testa) Thermal spraying
This technique of cooling system, which is often used
at Paul Sherre Institut (PSI) laboratory, is that cladding by
spraying is operated on Stainless steel piping and copper
plate along groove. We used aluminium wire spraying tokeep high thermal conduction and avoid corrosion.

Air gap
50mm

Fig. 6 Cross section of thermal sprayingb) Friction Stir Welding (FSW)
FSW is a gluing method which flows and agitates theinside of mother material by friction. At first we cut
cooling paths groove, and cover with the copper cap.
Finally FSW was applied along the gap between bank andcap.
The advantage of this method is high heat transfer rateby the direct cooling and low cost. But for direct cooling
we must pay attention to erosion and corrosion problems
at surface of OFC.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

Fig.7 shows a mock-up of FSW cooling test. We canapply heat to this up to 20 kW from the back side. A water
path with 6 turns is fabricated in the copper plate. We will
test the heat convection with this model soon.

6. Restart experiments in second phase.
It is remarked that we have to install large radiation
shield in front of the beam dump in order to avoid theradiation exposure from the inside of the highly-activatedcopper core. The adequate thickness of the radiation
shield must be carefully evaluated to establish thescenarios of moving and daily maintenance.

6. SUMMARY AND PROSPECT
Water in20kW•

Water out
Fig.7 Mock-up for cooling test with FSWC) Gun drill
Gun drill is a conventional drilling method to make along hole in the metal block. The maximum length of ahole can be 50~100 times as long as the diameter of thehole. Thus, the cooling paths can be easily made in OFCcore, making holes and connecting them.
This device has the same advantage and disadvantage
as FSW because of direct cooling at surface of copper.

••

4. HOW TO MOVE
Residual dose rate simulated by MARS
It is very important for moving the beam dump toevaluate the residual dose rate at contact for the beam
dump after the long-time irradiation of the beam because
we have to plan moving procedures in practice.
Fig.8 shows a typical result of the residual dose rate atcontact after 1-year irradiation of 50 GeV-15µA beamand half-year cooling. The dimension of OFC-core wasdetermined to be 3m W x 2m H, considering theacceptable radiation exposure during the moving work.
290 µSv/h
2.3 mSv/h
2.5 mSv/h•

The core of this beam dump is mainly made ofOFC, which is chosen for high heat conduction
and radiation resistance. The core part has aconical hollow in order to make proton beamdisperse in moderation.
Numerical analysis were performed with MARS
and ANSYS codes for checking the feasibility ofbeam dump about radiation and cooling, and wefigure out maximum temperature is 260°C morethan OFC’s softening temperature (200°C). For
falling in maximum temperature, we have to carryout that conical hollow is optimised, and heattransfer must improve more than 600[W/m2/K].
Now we are evaluating three cooling devices(thermal spraying, FSW and gun drill) of beam
dump for checking cooling ability, reliability andease to maintain and comparing with each other.
The scheme of moving beam dump to 50m
downstream was considered and needs to beestablished in detail.

ACKNOWLEDGMENTS
This work was partly supported by a Grant-in Aid for
Scientific Research (A)(2) and Sub-Committee for
Encouragement of Young Scientists (B), No. 15204024
and No. 15740166, of the Japan Ministry of Education,Culture, Sports, Science and Technology (Monbukagaku-sho).

REFERENCES
2m

62 µSv/h
3m

330 µSv/h

130 µSv/hFig. 8 calculation of residual dose rate
The weight of the beam dump, which can be moved todownstream, is ~1000 ton, and complete weight including
moving shield with a crane is ~2000ton. Moving
procedure is planed to complete in one day., and floor isable to sustain as heavy as 2000ton. We take into
consideration of these, and here are moving scheme:
1. Shutdown experiments in first phase.
2. Cool nuclear radiation for half or a year.
3. Extension works, and cure cooling, thermocouple
thermometer and vacuum devices
4. Move to 50 meter downstream.
5. Reinstall peripheral devices.

[1] K. AGARI et al., “Design of slow extraction beamline at 50GeV-PS in the High Intensity Accelerator
Facility”, Proceedings of the 13th Symposium onAccelerator Science and Technology, October 2001,p. 464-466[2] Y. Yamanoi et al., “Design of the production targetfor slow extracion beam lines at K-hall”, Proceedingsof the 13th Symposium on Accelerator Science andTechnology, October 2001, p.393-395.
[3] 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",
Fermilab-Conf-98/379 (1998); LANL Report LAUR-98-5716 (1998); nucl-th/9812038 v2 16 Dec
1998. N.V. Mokhov, "MARS Code Developments,Benchmarking and Applications", Fermilab-Conf00/066 (2000).