The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Development of Compact Proton Synchrotron with Combined Function
Dedicated for Cancer Therapy
Akira NODA, Yoshihisa IWASHITA, Makoto INOUE, Akio MORITA, Toshiyuki SHIRAI, Masatsugu NISHI*,
Kazuo HIRAMOTO*, Jun'ichi HIROTA**, Masahiro TADOKORO** and Masumi UMEZAWA*
Institute for Chemical Research, Kyoto University
Gokanosho, Uji-city, Kyoto, 611 JAPAN*Hitachi Research Laboratory, Hitachi Ltd., Hitachi shi, Ibaraki, 319-12 JAPAN** Hitachi Works, Hitachi Ltd., Hitachi shi, Ibaraki, 317 JAPANAbstract
A compact proton synchrotron with combined function
lattice has been developed to be dedicated for cancer therapy.
Its maximum energy and the circumference are 250 MeV
and 23.9 m, respectively. A ring with 6-fold symmetrycomposed of 6 identical combined function magnets of the
focusing structure of FDF has been adopted in order toavoid the effect of sector resonances. By the calculation withuse of 3 dimensional code TOSCA, the operation point of
the betatron oscillations is expected to remain well close to
the desired value of (1.70, 1.75) in the wide excitation levelup to 1.35 T.
1 Introduction
Recently cancer therapy has become one of the mostimportant item for human welfare because about one thirdof the people die for cancers. In Japan, group of Universityof Tsukuba has achieved good results with proton therapy
and in these few years, heavy ion therapy has become
available after the completion of world first dedicatedheavy-ion synchrotron, HIMAC in Chiba. The number ofpatients who fortunately receive such benefit, however, islimited to rather smaller value compared with those whoneed such charged particle therapy.
In Kyoto University, efforts to realize particle cancer
therapy has been continued succeeding the will of late Prof.
Hideki Yukawa who wanted to utilize the attainment ofphysics for human welfare and at the first stage, pion
therapy has also been pursued together with proton andneutron therapies[!]. In recent years, however, a proton
facility called KUMPF has been proposed for the merit ofcompactness both in size and cost[2]. On the basis of suchapproach, we are aiming at establishing a prototype designof dedicated proton synchrotron for cancer therapy, which
can be operated in hospitals without experts of accelerator.
Main difficulty in operation of synchrotron resides incontrol of RF system and tracking of excitation currents
between dipole and quadrupole magnets. From the point ofview of easy daily routine-operation, we do not need muchflexibility, but the fewer the freedom of operation, theSMl

Sl\12 to Beam Transport LineFig. 1 Combined Function Proton Synchrotron.
better. So as to respond such requirement, we havealready constructed a real power untuned-RF cavity wellsuited for daily routine operation[3].
So as far assynchrotron ring is concerned, the operation will become
very easy if the combined function lattice works wellbecause no tracking between dipole and quadrupole isneeded, although its design is somewhat difficult. From
this point of view, we are making main efforts to establish
reliable design of combined function lattice. In Fig. 1, theproposed lattice with 6-fold symmetry is shown. Eachmagnet deflect proton as large as 60° and has focusing
Beta and Dispersion Function·--i\.............t).-\........ /:..............

+----<!

6 1-··············: ................
iiI i \\.
I.3is =:-:~:~~~<;r0) 1··-\·r····j·······i/··+············· .z~

4_~ .D,(m •······-:--·····\···r··/y···(··········· ·::1::~.
1·10234.8

Distance along the Orbit (m)II'IIB:.comhined FWiction I\..fagnet)

Fig. 2 Beta and dispersion functions for one superperiod.

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The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 199,7

Table 1Main Parameters of Combined Function ProtonsIVnChrotron
250 MeV
Maximum Energy
Radius of Curvature

1.9 m

Circumference

23.9m

Maximum Magnetic Field athe Central Orbit

1.281

Lattice Structure

OFDFO

Operating Point(1.70, 1.75(a)" ".---:---;--,---,---,-.,....-,-,-,---::-=-r--;:-~--:--r-~-:--,---,~o~bi~ed: Func~ion; M~gn;et0. 0 s.

j'''jjj: : : :---~----t---·t····t···- ----~----~----~----)-----

jlji.'

1''': : : : -- --··{····{----~-.
··{··.
----:-----:-----:----+'

f:::li±il. .•t~f:~ll"" I : i i=:~~~~G! I ! :""j\~\~l' IR60°

Bending Angle of theMagnet(b) " '" ,--,--r--:--c--r::;-~c--=-.-:r-:-:-:.,--,-:-r-:~--:---:--,

F: -5.855, D:6.16L

n-values''..

structure of FDF. In Fig. 2, beta- and dispersion functionsof this lattice are shown for one superperiod. Main optics
is solely based on these 6 magnets, while two trimquadrupoles are added considering correction of operationpoint. These trim quadrupoles are expected to become
ll340 j--...J970

R~t-.,.-----R-1-90---'0'-'-____.,.j-"-----R-23-1-'-0-=e::i__,

R

270

340

120

120

120800Fig. 3(a)F sector Correction Coil

Main Coil--I
970
I~~~.,.-----R-1-90-0-~~----R-2--31~

270

800

Fig. 4 Calculated Field Distribution in F (a) and D (b)sectors.
unnecessary once the final good design is fixed byconstruction of the prototype machine, hopefully at Kyoto
University. The budget for the whole ring, however, is not
approved yet, but we are now constructing only one of thesix identical combined function magnets in order to fix thedesign. Main parameters of the ring are listed up in Table
1. In the following sections, design of the model magnet
are described.
2 FDF Magnet with Combined Function
The magnet has the structureofFDF, where each section
has deflection angles of 15°, 30° and 15°, respectively.
With the calculation assuming sharp edge as the starting
point, the n-values needed for F and D sections arecalculated to be -5.855 and 6.164, respectively to realize theoperation point of (1. 75, 1. 75). The pole shape has been
determined to make the equipotential surface of themagnetic potential given as

Fig. 3 (b)D sector

k2 2(jJ = -B0 y[ l+k1x+-zx201700

1950

X

Fig.3(c)Pole profiles ofF (solid line) and D (dashed line).

JY2 ] ,kl
-61 ( P+k2

where x andy are the radial and vertical displacements fromthe central orbit, p is the radius of curvature of the centralorbit and B0 is the magnetic field at the central orbit[ 4]. In
the present design, the sextupole component is desirable to--315--

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997
1.9

1.85

I-; :~rget·G. O.Odeg~tune

1-~0.1d~"'1.75~···--~ ~...

1.7~?.4deg

1.65
1.64
X2600.0

I

Fig. 5 Transition region assumed in the 3 dimensional
calculation by TOSCA.
be as small as possible and we imposed the condition k2
should be zero. In addition to this, several slots are madein the pole in order to keep the magnetic field strength
constant in the whole pole region while the magnet field at
the gap has large gradient. In Fig. 3(a) and (b), the crosssection ofF and D sectors are shown and the precise poleshape profiles are shown in Fig.3(c) for F and D sections bysolid and dashed curves, respectively.
3 Field Calculation with 2 Dimensional CodeWith this pole shape, the expected field distribution withcylindrical symmetry is obtained by 2 dimensional code
P ANDILA. In Fig.4, the field distributions are shown for
full range of excitation levels. It is found that in the widefield levels between 0.4 and 1.35 T the good field region isrealized for ±50 mm[5].

transition region between F and D-sectors ..

1.7

1.72

1.74

1.76

5 Evaluation of Tune Values
Using the magnetic field map obtained by suchcalculations, two dimensional field distribution in the
median plane is Fourier expanded, which is extrapolated to3 dimensional distribution in the nearby region of themedian plane with the relation V X B = 0. The equationof motion of proton beam is solved with this field
distribution[8]. In order to realize desirable tune values
for radial and vertical directions, the deflection angles ofFand D sections are adjusted keeping the total deflection to be60°. In Fig. 7, the result of such estimation is shown and it
is known that the modified operating point of (1. 70, 1. 75)
will be attained by selecting the deflection angles of
15.24 o and 59.52° for F and D section, respectively.
Acknowledg ment

In order to avoid the saturation at the sharp edge of ironcore, both ends of the magnet are designed to approximate
the so called Rogowski's curve[6] by 5 steps in the regionof ±70 mm length along the orbit. Further the transition
regions between F and D sections also have such structure as
illustrated in Fig. 5.
Three dimensional field calculation
has been performed with use ofcomputerc odeTOSCA In
Fig. 6, typical example of the field variation along theFie~d variation along the central orbit in the1.68

Fig. 7 Estimated betatron tune from field distribution.
central orbit in the transition region between F and D sectors
obtained with the three dimensional calculation is shown.

4 Three Dimensional Field Calculation with TOSCA

Fig. 6

1.66'xyThe work presented here has been supported by Grantin-Aid for Scientific Research from Ministry of Education,
Science, Sports and Culture of Japan.
References[1] H. Takekoshi, "Proposal for a University Accelerator
Facility for Physics and Medicine", Proc. of the 4th Syrup.
on Accel. Sci. and Tech., RII<EN, Japan, (1982) 279.
[2] A. Noda et al., "Dedicated Accelerator Project forProton Therapy at Kyoto University", Proc. of NIRS Int.
Seminar in connection with the 21st PTCOG Meeting,Chiba, Japan (1994)292.
[3] J.I. Hirota et al., "An Untuned Type RF Cavity using
Multiple Power Feeding", Proc. of the lOth Symp. on Accel.
Sci. and Tech., Hitatinaka, Japan (1995)25.
[4]K. KakiKawa et al., 'The KEK Boosrer Magnet", KEK75-3.
[5] M. Tadokoro et al., Proc. of PAC1997, Vancouver,
Canada (1997) in print.
[6] W. Rogowski, "Die Elektrische Festigkeit am Rande desPlatrenkondensators", Archiv fur Elektrotechnik, 7(1923) 1.
[7] A. Morita et al., to be published in ICR Activity Report,''Beam Science and Technology", Vol. 3.

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