Preliminary Measurement of the Magnetic Field in the Aperture of theVery High Field Short Pulse Dipole Magnet for Compact Synchrotron
S. Tokura, M. Hara, K. Uematsu, S. Nakajima, and Y. Miyauchi, Ishikawajima-Harima
Heavy Industries LTD., Yokohama, Japan
S. Komiya, T. Ito, H. Tsutsui, S. Tsuji-Iio, and R. Shimada, Tokyo Institute ofTechnology, Tokyo, Japan

Preliminary measurement of the magnetic fieldin the aperture of the very high-field, short-pulse
dipole magnet is presented. The dipole magnet isapplied for a compact proton synchrotron
dedicated for cancer therapy. After numericalanalysis for the design of coil geometry of thedipole magnet using 3 dimensional field
simulation, test machine of the dipole magnet hasdeveloped. Besides, the special equipment for themeasurement of the field in the aperture are also
made. Preliminary operation for exciting the fieldin the aperture to the maximum magnetic flux
density of 4 [T] is carry out, and measurement
data are compared with data of the field
simulation.

The authors have studied the feasibility of theproton synchrotron of the type of STAC, andshowed that dynamic aperture is increased by theimprovement of the design of bending magnet [6].
The new design of the cross-section of current
conductor of the bending magnet considerably
decreases sextupole field component [7, 8]. Theauthors have also reported the feasibility of thelattice composed of four bending magnets andfour quadrupole magnets from the standpoint ofdynamic aperture using detailed distribution of
the multipole coefficients of bending field [9].
This paper introduces about the high-field,
compact dipole magnet which the authors havedeveloped based on results of numerical fieldsimulation, and also reports the preliminary
measurement of the field in the dipole magnet.

1 INTRODUCTION

2 MAIN PARAMETERS

Radiation therapy using high-energy proton has
been proved to be very effective method of cancer
treatment. On the other hand, it is not widely used
due to its very high cost and large area required
for the total system. Considering that theaccelerator occupies the major parts of the system,
reduction of its size and cost is strongly required
for the spread of this effective therapy system.
A challenging idea of proton synchrotron usingpulse high field (5 T) magnet was proposed by
BINP [1], and component development has been
made [2]. As the joint study of Frascati and BINP,
Picardi et al (Frascati) [3,4] relaxed theparameters of the original BINP design, andproposed a moderate design of the maximum
bending field of 4 T (referred to as “STAC” in thepapers). Using more relaxed bending field of 3 T,
Endo (KEK) et al. proposed a design of better
feasibility to realize a very small carbon
synchrotron [5], which is also strongly requiredfor cancer treatment.

A compact 200 [MeV] proton synchrotron withthe injection energy of 3 [MeV] has been
proposed [6-9]. Four bending magnets and fourquadrupole magnets compose the basic lattice asAbstract

QD SXTBMSXTQDBM

Average diameter=2.02 [m]BM=Bending Magnet
QD=Defocus Quad
SXT=Sextupole Magnet

QD
SXT
BMBM
SXT QD

Figure 1 Lattice layout

Table 1 Main parameters

shown in Figure 1. Four sextupole magnets arealso prepared for the compensation of sextupole
component of the magnetic field that may begenerated near the edge of the bending. As theouter dimension is about 2.1 [m], it can betransported to hospitals after the assembly andtuning in the factory. Main parameters ofsynchrotron and its bending magnet are listed inTable 1.

3 DIPOLE MAGNET
Figure 2 is the photograph of the full-size
dipole magnet. The bending radius is 0.54 [m],and the bending angle is 90 [deg]. The magnet
core is consisted of silicon steel sheets with athickness of 0.5[mm]. In order to laminate siliconsteel sheets with high density, each silicon steelZX

One turn coil

Y 20ZO76X

52Value
200 MeV (644 MeV/c)
3 MeV (75.1 MeV/c)
RFQ
6.473 m0.54 m0.42 - 4 T
0.052 / 0.020 m
90 deg0 deg
3.5 ms4
1.469 / 0.420
1.395 / 2.641 m
0.596 / 0 m-0.049 / -0.346
3.86 – 27.4 MHz
1144

Item
Extraction energy, T ext
Injection energy, T inj
Injector typeCircumference, C
Bending radius, rBending field, B
Gap height / width, h / w
Bending angle
Edge angle
Acceleration time
Super period
Betatron tune, νH / νV
Betatron function (Max.), βH /βVDispersion (Max.), ηH /ηV
Natural chromaticity, ξH /ξVRF frequency, fRF
Harmonic number, hY

20
Laminatediron144

Figure 3 Conceptual cross-sectional viewof the bending magnet
sheet is welded with seven steel bars under thecondition where silicon steel sheets are clampedwith special device firmly. Besides, considering
the maintenance of the duct in the aperture, themagnetic core can be divided into two blocks(lower and upper sides). Figure 3 shows theconceptual cross-sectional view of the bendingmagnet. The current pattern for field excitation isthe quarter of the sine curve, and its current risingtime is 3.5 [ms]. In order to get the maximum
field of 4 [T], the magnet is excited by highcurrent of 200 [kA] using single turn copper bus.

4 MAGNETIC FIELDMEASUREMENT

Figure 2 Photograph of the full-size
dipole magnet

Figure 4 shows the diagram of the pulsed
power supply for preliminary measurement of themagnetic field of the dipole magnet. The time
shape of the current is a quarter sine function with3.5 [ms] duration, which comes from thedischarge of a 2.7 [mF] capacitor bank. The
transformation ratio is 100:9.
The magnetic field measurements are
performed using a set of 5 search coils to obtainthe values of the magnetic field on X axis. The

Ignitron

Dipole Magnet

Figure 4 Diagram of the pulsed power[4] L. Picardi et al, “Preliminary Design of aTechnologically Advanced and Compact (STAC)
for Proton therapy, Hadron therapy and Oncology”,
1994, pp367-376[5] K. Endo et al., “Table-top Proton Synchrotron Ringfor Medical Applications”, EPAC2000, Vienna,
2000, pp2515-7.
[6] Y. Miyauchi et al., “Preliminary Study of theFeasibility of Pulse High Field Compact
Synchrotron for Medical Use”, Kyoto Univ.
activity report, Vol.6, 2001.
[7] S. Tokura et al., “Very High-Field Short-Pulse
Dipole Magnet For Compact Proton Synchrotron“,
PAC’2001, Chicago, 2001.
[8] S. Tokura et al., “Design of the Very High-Field
Short-Pulse Dipole Magnet“, The 13th
Symposium on Accelerator Science andTechnology, Japan, 2001, pp271-273.
[9] S. Tokura et al., “Study of the Dynamic Aperture ofthe Pulse High Field Compact Proton Synchrotronfor Medical Use”, Kyoto Univ. activity report,Vol.7, 2002.

values of the magnetic field in the direction of thebeam orbit are also measured. Figure 5 is thetypical result obtained from 3 dimensional
magnetic field simulation. This figure shows thedistribution of the sextupole component in thedirection of the beam orbit near the edge of thedipole magnet at extraction (200 [MeV]). The
measurements of the magnetic field are mainly
performed near the edge of the dipole magnet
because of the figure suggesting the increase of
the sextupole component near the edge.

6 SUMMARY
The proto type of the very high field short pulse
dipole magnet has been developed, andpreliminary field measurements have beenperformed. The values obtained from fieldmeasurements are compared to the result of the 3
dimensional magnetic field simulation.

ACKNOWLEDGEMENT
The authors would like to thank Dr. K. Endo
(High Energy Accelerator Research Organization)
for valuable advice and helpful suggestions to thisresearch. They also thank Tokin Machinery
Corporation for great help.

REFERENCES[1] I. Averbukh et al., “Project of Small-Dimensional
200 MeV Proton synchrotron”, EPAC’88, Rome,
1988, pp413-6.
[2] “Prototype of the Proton Synchrotron with 5-Tesla
Dipole Magnets”, BINP annual report, 1998,
pp207-9.
[3] L. Picardi et al., “Preliminary Design of aTechnologically
AdvancedandCompact
Synchrotron for Proton therapy”, ENEA, 1994.

Sextupole field component B2 [T/m^2]

supply of the dipole magnet
200.0
150.0
100.0
50.0
0.0
-50.0
-100.0-150.0-200.00.0

100.0 200.0 300.0 400.0
Z [mm]

Figure 5 Sextupole component in thedirection of the beam orbit (200MeV)