Proceedings of IBIC2012, Tsukuba, Japan

MOPB68DEVELOPMENT OF PROFILE MONITOR SYSTEM FOR HIGHINTENSE SPALLATION NEUTRON SOURCE
Shin-ichiro Meigo∗ , Motoki Ooi, Kiyomi Ikezaki, Atsushi Akutsu, Shinichi Sakamoto
and Masatoshi Futakawa, J-PARC center, Japan Atomic Energy Agency (JAEA), JapanAt the JSNS in J-PARC, a mercury target is employed as
the neutron production target. It is well known that thedamage on the mercury target is proportional to the 4th
power of the peak current density of the primary proton
beam on the target. For the high intense neutron source, theprofile on the target is important to drive the neutron sourcewith the continuously observation of the profile. We havedeveloped to Multi Wire Profile Monitor System (MWPM).
During beam operation, when the abnormally of the beam
is found, the beam is cut out by the Machine Protection
System (MPS). For the measurement of the two dimension
observation on the target, we have developed the system
based on the residual radiation measurement by using an
imaging plate (IP). It is found that the beam width observedby the MWPM and the IP shows good agreement.

at the JSNS especially for the peak current density. We
have developed a reliable beam profile monitor for the target by using Multi Wire Profile Monitor (MWPM). In orderto watch the two dimensional profile on the target, we havealso developed the profile monitor based on the imaging ofradiation of the target vessel after beam irradiation.

INTRODUCTION
In the Japan Proton Accelerator Research Complex (JPARC) [1], an MW-class pulsed neutron source, the Japan
Spallation Neutron Source (JSNS) [2], and the Muon Science facility (MUSE) [3] will be installed in the materials
and life science facility (MLF) shown in Fig. 1. The 3GeV proton beam is introduced to the mercury target fora neutron source and to a carbon graphite target of 20 mm
thickness for a muon source. In order to utilize the proton
beam efficiently for particle productions, both targets arealigned in a cascade scheme, where the graphite target is
located 33 m upstream of the neutron target.
For both sources the 3-GeV proton beam is deliveredfrom a rapid cycling synchrotron (RCS) to the targets by
the 3NBT [4, 5, 6]. Before injection to the RCS, the proton
beam is accelerated up to 181MeV by a LINAC. The beamis accumulated in short two bunches having width about
150 ns and accelerated up to 3 GeV in the RCS. After extraction, the 3-GeV proton beam is transferred to the muon
production target and the spallation neutron source.
Recently it became evident that pitting damage appears
in the target container of the mercury target [7]. Several facilities are studying the effect; Alternating GradientSynchrotron (AGS) and Weapon Neutron Research facility (WNR) are pursuing off-beam experiments [8]. It has
been reported that the damage is proportional to the 4th
power of the peak current density of the beam [8]. Beamprofile monitoring plays an important role in comprehending the damage to the target. Therefore it is very important
to watch continuously the status of the beam at the target∗ meigo.shinichiro@jaea.go.jp

Figure 1: Layout of JSNS and MUSE at J-PARC. The beamtransport line (3NBT) introduces the beam to both facilities
located in the MLF building.

MULTI WIRE PROFILE MONITOR
Silicon Carbide (SiC) Wire
In order to obtain the characteristics of the proton beam,diagnostic system based on a Multi Wire Profile Monitor(MWPM) is developed. Principle of the MWPM is simple
to observe the amount of the electron emission due to theinteraction of the beam at the wire. As a material of sensitive wire, usually tungsten wire is selected due to large
emission amount of the electron and having high temperature melting point. In the present system, silicon carbide(SiC)is chosen due to the high resistance of the radiation.
Due to the interaction, the beam loss is caused, which isone of issues of the high intensity proton accelerator andthe optimization of the beam loss is important. The angular differential cross section of Rutherford scattering is
proportional to square of atomic number of wire material.
Therefore wire material with low atomic number has advantage for beam loss. Here, we compare property between
tungsten and SiC. Since the average atomic number of SiC
is 10, the differential cross section of SiC becomes 1/55
times of the cross section of tungsten. In order to obtain
the angular distribution after scattered by the wire is calculated with DECAY-TURTLE [9] modified at PSI [10].
It is recognized that SiC wire than tungsten gives less influence on the beam. In order to estimate of the lifetime
ISBN 978-3-95450-119-9

Transverse Profiles, Screens & Wires Monitors

1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○AbstractMOPB68

Proceedings of IBIC2012, Tsukuba, Japanof monitor wire, the displacement cross section of DPA is
calculated with NMTC/JAM [11]. By the calculation, it
is found that the DPA cross section of SiC and tungsten
for 3-GeV proton is 278 and 7997 barn respectably, whichshows that DPA of the tungsten is about 29 times larger
than SiC. Furthermore, it is known that the SiC can standup 100 DPA. Therefore we chose to use SiC as wire of as astandard model of the profile monitor.

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○MWPM
The view of MWPM is shown in Fig. 2. Along the beamtransport line, 15 sets of movable MWPMs is placed tomeasure the beam profile. The MWPM frame has 31 wiresof SiC with the spacing pitch of 6 mm for each horizontal
and vertical directions. We employed the SiC wire having diameter of 0.1 mm, which has a tungsten core of 0.01
mm and is coated with 1μm of pyrolytic carbon. The wire
frame made of aluminum oxide with purity more than 95 %is selected due to the high radiation resistance. In order tosustain with the fixed tension, wires are kept by the holder
with spring, which gives the unique tension of 0.6 N to thewire. The frame of wires is placed in the vacuum chamber
made of titanium, which is selected by the following reason, good vacuum characteristics and low activation. In order to avoid unnecessary irradiation of the wires, the frame
can retract and moves like the pendulum motion. During
the profile measurement, the beam loss due to the scattering at wires was observed by the beam loss monitor. For
the practical aspect, beam loss cased at the MWPM canbe utilized to confirm good performance of the beam loss
monitors.

Profile Monitor at the Proton Beam Window(PBW)
It is important to watch continuously the characteristicsof the proton beam introduced to the spallation target. Dueto the high activations caused by the neutron produced at
the target, remote handling technique is necessary to exchange the beam monitor for the target. In order to decrease the radiation produced at the spallation neutron target, shieldings above the monitor are required. To decrease
the difficulties of the exchange work and decrease of theshielding, we combined the MWPM with a Proton BeamWindow (PBW) for separation between the vacuum regionof the accelerator and the helium region around the neutron target. The PBW is better to be placed closer to thetarget where distance between the target and the PBW is
1.8 m, which gives reliable profile at the target. In Fig. 3,
the MWPM placed in the PBW is shown, which has the
MWPMs in the center of the chamber. In order to avoid
over heat load at target vicinities, beam halo monitors areplaced as well. The chamber of the PBW has inflatable sealcalled pillow seal. Due to the pillow seal, we can exchange
MWPM by the remote handling.
Wires at the MWPM on the PBW are continuously irradiated to the beam so that long life time is required. Since
the monitor at the PBW is important, redundant system of
the wire is utilized. In order to give the life time information about the wire for the future, both SiC and tungsten
wires are placed.

Figure 3: MWPM placed at the Proton Beam Window(PBW).

Figure 2: Movable MWPM placed at the beam transport
line. (top: MWPM and frame inside the vacuum chamber.
bottom: MWPM and chamber placed in the beam transport
line.)For the tuning of the accelerators, we have the beam
dump located at the extraction section of the RCS madeof iron, which has capability of the beam load of 8 kW.
In order to watch the status of the beam toward the beamdump, another stationary MWPM is placed in front of thebeam dump. During the beam tuning, the LINAC beam
without circulation and acceleration at the RCS is directly
introduced to the dump especially for tuning of the RCS

ISBN 978-3-95450-119-92Transverse Profiles, Screens & Wires Monitors

Proceedings of IBIC2012, Tsukuba, Japan

MOPB68

injection. The time structure of the LINAC beam has awidth of 0.5 ms in total with chop having the width of
600 ns. Although the time structure and the energy of thebeam is completely different between LINAC and RCS,
the MWPM gives reliable result of the beam profile, whichhelps tuning the accelerators very well.

Signal of the SiC Wire

Figure 5: Beam profile obtained by the MWPM locatedat the proton beam window for 0.3 MW beam. Top andbottom graph shows the result for horizontal and verticaldirection, respectively.
an aluminum foil (0.3mm in thickness) on the target, thebeam profile was obtained from the residual dose distribution on the foil. After irradiation, the foil is removed fromthe target then foil is attached to the imaging plate (Fujifirm BAS-SR 2040) to read the dose distribution. Figure 6
shows the observed result.

Figure 4: Signal of the MWPM after shaped by the inverter
amplifier (yellow).
In Fig. 5, the beam profile at the PBW obtained by thepresent system is shown. Each result is fitted by the Gaussian and base distribution for every second. Result of thecenter position and the width is utilized to watch the statusof beam injected to the target.

PROFILE MONITOR BY THE IMAGING
PLATE



Figure 6: Beam profile observed by the activation of thealuminum foil(0.3mm-t) located on the spallation neutron
target (one division in figure is 10mm).

Imaging by Activation Aluminum Foil
In the beginning of the beam commissioning, we measured the profile by the activation technique using aluminum foil placed on the target vessel. In order to achieve
good performance at the neutron source, enough space is
not remaining around at the target to put any devices forthe beam profile measurement. To fit the requirement withthe tiny space around the target, we performed to activation technique which requires only thin foil space. Placing

Imaging Plate Attached to the Target After Beam
Irradiation
In order to perform beam profile measurement by the activation, access to the target is necessary after beam irradiation. The radiation around the target is extremely high suchas several tenth Sv/h therefore a remote handling technique
is required. We have developed an activation technique byISBN 978-3-95450-119-9

Transverse Profiles, Screens & Wires Monitors

3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Signal of the SiC wire after shaped amplifier is shown in
Fig 4. All signals of MWPM is transfer to the local control
room by twisted pare cables with high radiation Harding.
As for the MWPM of the PBW, Mineral Insulator Cables(MICs) are applied because the cables receives quite highradiation does more than 1 MGy. The signal is fed to theinverter amp (Technoland N-GK 160 32ch Inverter AMP)
and fed to the charge collective ADC (Technoland C-TS
301B) with the integration time range of 3 μs, which has
integration charge range of -3000 pC in total and is driven
by the CAMAC bus. The signals on the CAMAC bus areread out via crate controller of Toyo CC/NET. All signals
is controlled by the EPICS [12] and is data base server.

MOPB68

Proceedings of IBIC2012, Tsukuba, Japanutilizing the IP. By remote handling technique, the IP is attached to the mercury target vessel shown in Fig. 7. The
IP contained in holder was attached to the hook of in-cellcrane by human hands. Around the entrance of hot cell,radiation was several tenth of μ Sv/h so that human canaccess. The IP approached to the target by the crane andcontacted with the target by help of the master slave manipulator as shown in Fig. 7. Typical duration of exposure
time was 5 min. After the exposure, the image of radiation
was read out by the reader of the IP.

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 8: Two dimensional beam profile obtained by the IP
attached to the target vessel.

Figure 9: Beam profile in horizontal direction obtained by
the IP with fitting of two Gaussian curves.

DISCUSSION
Comparison of Beam Widths Obtained by
MWPM and IP
Figure 7: Activation technique using Imaging Plate (IP)located on the target vessel performed after irradiation at
hot cell of the MLF. (top) IP holder placed crane (bottom)
IP attached by the master slave manipulator.

In Fig. 10, beam width for horizontal and vertical directions observed by the MWPM and the IP is compared asfunction of the beam run. The MWPM result is collected
to become the width at the target by taking account of thebeam gradient. As increase of the run number, the beam is
gradually expanded due to decrees the damage of the target
vessel. It is found that the beam width considerably agreewith each other. Agreement of the width implies that reliable width can be obtained by the present profile monitor
system. By using the MWPM, the present beam width canbe obtained each beam pulse.

Figure 8 shows the beam profile obtained by the activation technique with the IP after 120 kW beam operation.
In the distribution, it is shown that a clear Gaussian peakexists without skew of the beam, which was also presented
by foil activation technique.

Machine Protection System

The beam profile in horizontal distribution obtained by
the IP is shown in Fig. 9. The distribution can be welldescribed by the combinations of two Gaussian functions
having small and large widths. The smaller one wasthought to be the initial protons. The larger width wasthought to be the secondary particles mainly neutrons. By
using the shorter width, we obtained the primary beamwidth at the target.

Data of the beam profile for every shots are watched by
the control system driven by the EPICS and are stored indata base. If any anomaly of the beam was found, such as
offset of the beam position, the beam should be immediately stopped for the safety reason. We have developed themachine protect system (MPS), which cut out the beam if
the beam offset exceeded the threshold. Under the present
protection system, high power beam operation of 1 MW
can be performed with high confident.

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Proceedings of IBIC2012, Tsukuba, Japan

MOPB68REFERENCES[1] The Joint Project Team of JAERI and KEK, JAERI-Tech
99-56, 1999.
[2] Y. Ikeda, Nucl. Instrum. Meth. A600, (2009) 1.
[3] Y. Miyake, et al., Physica B 404 (2009) 957.
[4] S. Meigo, et al., Nucl. Instrum. Meth. A562, (2006) 569.
[5] S. Sakamoto, et al., Nucl. Instrum. Meth. A562, (2006) 638.
[6] S. Meigo, et al., Nucl. Instrum. Meth. A600, (2009) 41.
[7] M. Futakawa, et al., J. Nucl. Sci. Technol. 40 (2004) 895.
[8] M. Futakawa, et al., J. Nucl. Matter. 343 (2005) 70.

CONCLUSION
We have developed MWPM system by using SiC wires
to built reliable and long life profile monitor system at the
JSNS in J-PARC. In order to obtain two dimensional beamprofile at the target of the spallation neutron source, it wasdeveloped that beam monitoring technique based on theactivation technique by using the IP and remote handlingdevices. It is shown that the beam width obtain by the
MWPM agrees with the result by the activation result by
IP. Under the present profile monitor system, high power
beam operation such as 1 MW can be performed with highconfident.
Up to beginning of July 2012, the profile monitor wire
has received the beam with the integration of about 1000
MWh. Even such high integration of the beam power, still
both SiC and tungsten wires at the profile monitor of proton beam window are survived. In the next year, we haveplan to exchange the proton beam window and the profile
monitor.

[10] PSI Graphic Turtle Framework by U. Rohrer based on a
CERN-SLAC-FERMILAB version.
[11] K. Niita, S. Meigo, H. Takada and Y. Ikeda, JAERIData/Code 2001-007 (2001).
[12] M. Ooi, et al., ICANS-XVII, 17th Meeting of the International Collaboration on Advanced Neutron Sources, April
25-29, 2005, Santa Fe, New Mexico LA-UR-06-3904, 1152.

ISBN 978-3-95450-119-9
Transverse Profiles, Screens & Wires Monitors

5c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 10: Comparison of the beam width, which is root
mean square of the distribution, obtained by the IP and the
MWPM as a function of beam run.

[9] K.L. Brown, Ch. Iselin and D.C. Carey: Decay Turtle,
CERN 74-2 (1974).