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

DESIGN OF NEW SYNCHROTRON FOR HADRONTHERAPY
Akifumi ITANO, PhD.
Hyogo Ion Beam Medical Center
1-chome 2-1, Kouto, Shingu-cho, Ibo-gun, Hyogo, 679-5165, Japan
Abstract
A design of a synchrotron for hadrontherapy ispresented. The synchrotron accelerates carbon beam up to400 MeV/u and proton beam up to 230 MeV. It has superperiodicity 2 and two long straight sections with FODOF
structure and small dispersion, where multiturn injection
and slow extraction devices are located. Control ofchromaticity enables a superposition of the separatrices
with different momentum and minimum losses would beobtained at the electrostatic septum.

INTRODUCTION
Recent successful operation of medical accelerators forhadrontherapy with carbon beam, HIMAC at National
Institute of Radiological Sciences (NIRS) [1] and PATRO
at Hyogo Ion Beam Medical Center (HIBMC) [2],accelerated the hadrontherapy projects in Europe [3-5].
The designed synchrotrons all have super periodicity 2
and a circumference 60 – 80 m. We design a new
synchrotron with super periodicity 2 and two FODOF
structure long straight sections. This structure produces alarge phase advance in a transfer between an electrostatic
septum and a following septum magnet, and was very
successful at HIMAC and PATRO.

SPECIFICATIONS OF THE
SYNCHROTRON
Table 1 summarizes the specifications of synchrotron.
Figure 1 shows a layout of the synchrotron ring in ahorizontal plane. It has a 10-fold FODO structure withsuper periodicity 2. Figure 2 shows betatron anddispersion functions at nominal tunes (Qx, Qy) = (2.35,2.20). The ring has 2 long straight sections (FODOF) withsmall dispersion (< 0.3 m), which are used for a multiturninjection and a third order resonant slow extraction
respectively. This small dispersion results a large
dispersions (~7m) at other sections. Horizontal aperture
containing a corrected horizontal 3σ COD (±4mm) andmomentum envelope with maximum dp= ±0.7% at rf
capture is ±102 mm in focusing quadrupole. This gives anenough space for injection and to have a 10 mm spiralstep at extraction, where the momentum deviation would
be reduced to ±0.1%. Vertical aperture containing an
uncorrected 3σ COD (±12mm) is ±27 mm in defocusing
quadrupole.

MULTITURN INJECTION
Four fast bump magnets are used to form a bump orbit.
Entry point to the synchrotron of an injection electrostaticinflector (ESI) is 1.2 m upstream of a defocusing
quadrupole in FODOF long straight sections. Septum of
ESI is located at 44 mm from central orbit. Injection beam
enters the ring at 47 mm from the central orbit and withan angle – 8.7mrad. The requested number of turns is 20.
Emittances of injecting beam are assumed to be εxπ=εyπ=10π mm·mrad.
Table1. Specifications of the Synchrotron

Particles
Extraction Energy Range

Beam Intensity(Circulating beam)
Maximum Dipole Field
Tune ( Qx, Qy )Injection Energy
Max. βx / βyNatural Chromaticity ξx/ξyMax. Dispersion Dx
Acceptance (εxπ , εyπ)
Circumference
Super Periodicity
rf frequency
Spill length
Maximum Repetition Rate
Extraction

Proton and Carbon
100 -230MeV for p100-400MeV/u
forCarbon
5x1010 ppp for p
4x109 ppp for Carbon
1.433 T (rectangular type )( 2.35, 2.20 )5 MeV/u12.4 m / 23.1 m-1.063 / -2.2387m( 200π , 10π ) inmm·mrad
81.4 m2
1.1 – 7.9 MHz (h=3)
400ms
0.5 Hz for Carbon
1 Hz for proton
3rd order resonance at
7/3

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

are 250, 160 and 25 respectively in mm. Assuming amaximum induction Brff=10mT·MHz for Ni-Zn typeferrite, about 21 cores per half cavity are needed. Recentdevelopment of amorphous type magnetic alloy (such asFINEMET, VITROVAC6025F) gives a much larger
value of rf magnetic field strength Brf. Although this candecrease a number of cores required for the accelerating
voltage, it also decreases a shunt impedance of a cavity
and increases a required rf power. Anyway a large valueof µQF-product ~4x109 of amorphous alloy is interesting
to obtain a large impedance together with its low bias
current to control a permeability. With the amorphousalloy, the shunt impedance of the cavity is about 590Ω and the required amplifier power is 11 kW.

THIRD ORDER RESONANT SLOWEXTRACTION

Fig.1 Layout of the synchrotron ring.

Third order resonance at Qx=7/3 is used for slow
extraction. Two electrostatic deflectors ESD (<80kV/cm)
are located in a first part of FODOF long straight sections.
Two magnetic septa (0.5 and 1.5 T) are located in asecond part. Two sextupoles located in diametrically
opposite positions in the ring with inverse excitation areused for resonant excitation. This arrangement decouples
a separatrix control from a chromaticity control. The
sextupole with negative excitation is located at theposition with a phase advance p/3 θn downstream of thefirst electrostatic septum of ESD.
p/3 θn = p/3 θ0 + π/3 n = 5.69 rad with n=5, p=7p/3 θ0 = ϕesd – π/6
ϕesd = arctan (αx) = 0.975 rad
α x = 1.475 at ESD

Fig.2 Betatron and Dispersion functions of the ring.

RF ACCELERATION
A single-gap rf acceleration cavity, composed of twoquarter-wave ferrite-loaded coaxial lines excited inpush-pull mode with figure-of-eight bias current loops, islocated at downstream of ESI and defocusing quadrupolein FODOF section. As a dispersion function is small there,a beam phase and position monitor for rf frequency
control will be located in other straight section, wheredispersion is large. Required voltage is 5 kV (2.5 kV per
half cavity). Aperture of the vacuum chamber is 200 mm
in diameter. Outer, inner diameters and thickness of coreThis locates the sextupoles near focusing quadrupoles
and a large value of βx (~11 m) permits a moderate
sextupole strength 4 m-3 for resonance excitation atmaximum energy.
Four slow bump magnets are used to form a 20-mmbump at ESD septum. Septum is located at 65 mm apartfrom a central orbit. Figure 3 shows a simulation of beam
extraction. Initial εxπ is 20π mm·mrad, which is ahorizontal emittance at 400 MeV/u. Tunes are (Qx, Qy) =( 2.336, 2.20 ). Outward separatrix to the septum is nearlyparallel to the x-axis in horizontal phase space. At theposition of septum a spiral step is 10.2 mm and the beam
angle is –6.0 mrad for dp=0. This angle can be controlledwith an extra set of sextupoles.

HARDT CONDITION [6]The beam contains particles with different amplitude, xand x’, in a phase space and a certain momentum spread
dp. It can be represented as a series of ellipses (circles in anormalized phase space) for each dp. The circles become
triangles by a resonance excitation. The size of a triangle
corresponds to the last stable orbit. Any particles outside

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

the last stable triangle are lost along the outward
separatrices, as is shown in Figure 3. Due to thechromaticity in the ring, the momentum spread willtranslate into a tune spread. Particles in the beam withdifferent dp have the corresponding stable triangles inphase space with different sizes. Figure 4 shows threetriangles and corresponding outward separatrices for dp=0,±0.1% at the electrostatic septum. Chromaticities are set
at their natural values. In the figure, an effect of Dndp/p isneglected because the dispersion vector is very small(~0.082 m1/2). The separatrices are not superimposed andthe particles move outward along different trajectories
and reach the septum with different angles (d θ=±0.7mrad). This angular spread increases the effective
thickness of the septum and so a beam loss. The angularspread will be eliminated if all the separatrices can besuperimposed. This is achieved by the Hardt condition,
which can be obtained by a removal of dp dependent
terms from a general mathematical expression (withdispersion effect) of the separatrix. The Hardt condition isexpressed with following expression:

δµSDn
ζx

Dn cos (π – δµ) + D’n sin (π – δµ) = -4π/S ζx .
: phase advance from resonance sextupole to ESD: normalized sextupole strength: normalized dispersion vector at ESD: horizontal chromaticity.

Fig.3 Phase space representation of the extraction.

Fig. 4 Separatrices in the normalized phase space for
dp= -0.1% (outer), 0% (middle) and 0.1% (inner).

When the horizontal chromaticity is changed to –0.061
according to the condition, the three triangles in the figure
become almost of equal sizes and the separatrices aresuperimposed on that of dp=0.
Figure 5 shows the last 3-turn trajectories in the ring for
dp=0, ±0.1%. Particle trajectories do not interfere with theseptum of the injection electrostatic inflector (ESI) and iswell inside the vacuum chambers.
Computer simulation was done with a code WinAGILE.

REFERENCES[1] E. Takada et al., Proc. of the 13th Sympo.on Accel.
Sci. and Tech., Osaka, Japan (2001) pp.187-189.
[2] A. Itano, Proc. of the 13th Sympo.on Accel. Sci. andTech., Osaka, Japan(2001) pp.160-164.
[3] U. Amalidi et al., The TERA project and the Centre
for Oncological Hadrontherapy, INFN-LNF, Italy(1994).
[4] J. Debus, Proposal for a dedicated ion beam facility
for cancer therapy, DKFZ and GSI, Germany (1998).
[5] Projet ETOILE, rapport LYCEN 2002-1 (A,B,C),
Universite Claude Bernard Lyon 1, France (2002).
[6] W. Hardt, Ultraslow extraction out of LEAR, CERNInternal Note PS/DL/LEAR Note 81-6 (1981).

Fig. 5 Last 3-turn trajectories for dp= 0, ±0.1%.