JAERI-Conf 95-021

3a1-3
The optical design of HIMAC secondary beam course
Masahito Hosaka, Koji Noda, Tak:eshi Murakami, Mitsutaka Kanazawa,AtsushiKitagawa, Yukio Sato, Eiichi Takada, Masami Torikoshi
and Satoru Yamada
National Institute of Radiological Sciences
4-9-1 Anagawa, Inage-ward, Chiba-city, Chiba-prefecture, 263, Japan
ABSTRACf

A new beam course is under construction inHIMAC, NIRS, in order to utilize radioactive secondary
beams for medical purpose. The new course comprises adoubly achromatic spectrometer, which separates
projectile fragmentations. The design and the beam optics
are presented.
1. INTRODUCfiON
Application of radioactive beams[ I] is related tovast scientific areas, and one of the fruitful candidates is a
medical use. The heavy-ion accelerator complex for
medical use, HIMAC, began its operation in 1994 andcontinues treatment of cancer patients[2]. Great
advantages of charged-particle therapy, especially by
heavy ions, are the excellent dose distribution and thehigh biological effectiveness.
Although ranges and scattering angles in various
materials can be, in principle, precisely evaluated, small
ambiguities are left in evaluation of the dose distribution
inside human bodies because they are complicated mosaic
of soft and hard tissues. In order to fully utilize theadvantage of the charged particles, precise measurements
and/or confirmation of dose distribution inside bodies
under practical conditions are important.

-Combination of radioactive secondary beams of positron
emitters and annihilation y-ray detectors like PETs willrealize these measurements with no excessive dose.
Beams of 11 C and 19Ne are good candidates for thispurpose and are mainly quoted in the design stage of thenew course. On the other hand, other types of beams,
especially heavier ones, are taken into consideration inorder to expand experimental fields being carried out by
the new course. Therefore beam optics of three beamcourses are studied in order to maintain the versatility inthe future. One of the new courses is now underconstruction and will be completed in three years. This
paper describes design and beam optics of the new course.
2. BEAM OPTICS AND LAYOUT
Layout of the new course A layout of the new course
is illustrated in Fig. 1. The new beam course is a doubleachromatic fragment separator, comprising two bending
magnets, 11 quadrupole magnets, and an energy degrader.
The reaction products produced in the production
target, are separated from the primary beam by a 20°
bending magnet (BM01). The maximum magnetic
rigidity is chosen to be 8.13 Tm, which corresponds toq/A =l!l ions with an energy of 600 MeV/nucleon.

SLIT! SLIT2 SQ02 BMOl

production
target05lOrn

Fig. 1 Layout of IDMAC secondary beam course. The course denoted by SBLl isnow under construction.
11-410-11

JAERI-Conf 95-021

Dumping locations of primary beams varydependent on their magnetic rigidity relative to that of asecondary beam. Most of primary beams are stopped by a
movable beam stopper placed between an exit of themagnet, BMOl, and an entrance of a quadrupole magnet,SQ04. The exact separation of the fragments is performed
at a dispersive focusing position FO where the fragmentswith different magnetic rigidity are focused on thedifferent position. The dispersion D at FO is taken to be
the value of 1.87 (em/%). With an object size x0 =±0.3cm, at the production target, and then at FO the±0.28cm, the momentum
image size x (x,x)x 0
resolution is R = 2x!D = 0.30%. An achromatic energy
degrader of a wedge in shape can be inserted at FO, whichallows an additional fragment separation at the laterstage.
The second magnet, BM02, with a bending
angle of 26.5° and a pair of quadrupole magnets realize
the double achromatic condition that two chromatic terms(x,p) and (x',p) vanish hereafter. Thus, the image size ofthe secondary beam, which is broadened owing to its own
momentum spread at the dispersive focus FO, once moreshrink. When an achromatic energy degrader is placed at
FO, an additional isotope separation can be performed at
the second focusing point Fl. This second selection
based on the difference of the atomic energy loss in thedegrader, is essential for the separation of fragments ofheavier nuclei with whose magnetic rigidity one cannot
identify.
The three last quadrupole magnets gives the thirdfocus at F2 where irradiation of the radioactive secondary
beam is performed for medical purpose or for otherscientific research. The flexibility of using three
quadrupole magnets allow the focusing position to vary
to meet various requirements.

==i

As shown in Fig. 1., whole system is not
symmetric due to constraint that three beam courses
should be made within limited space. Although theoptimization process to attain double achromaticcondition may need a longer time than that of thesymmetric case, it essentially gives the same properties.
The beam optics was calculated using the code
MAGIC[3]. The design parameters and values of matrix
elements are summarized in Table 1 and the first orderbeam envelopes are shown in Fig. 2.
Table 1The parameters of the secondary beam course

Angular acceptance±13mrad±13 mrad±2.5%
8.13 Tm
11.9m to FO
22.6m to Fl
29.4m to F2
The ion optical matrix elements•>
F2FlFOMatrix element-0.35-0.93 0.87
(x,x)
0.000
(x,x) {cm/mrad] -0.000 0.000
0.000-1.87 0.000(x,p) [em/%]
0.000(x',p) [mrad/%] -0.26 0.000-2.1-1.75 0.86
(y,y)
0.000
(y,y) [cm/mrad] 0.029 0.010
verticalhorizontal
Momentum acceptanceMax. magnetic rigidity
Flight path lengtha) The matrix elements transfer inital values of X(), x• 0 and
Po as following.

x ) ( (x,x) (x,x') (x,p) )(xo)( x' = (x',x)(x',x')(x',p) x'opo(p,x) (p,x') (p,p)
p

0 ~--~++~~--~~~U--4~~~~~U-~~

~'0Qj

5

jloo

11:1

l:;lil

~10 01020

Distance along central trajectory (m)Fig. 2. The first order beam envelopes calculated fora initial parallelogram-like emittance of ±13 mrad inangle and ± 3mm in size
Solid line : with momentum spread±2.5%
Dashed line : without momentum spread-411-JAERI-Conf 95-021

Acce,ptance In general large values of beam emittanceand momentum spread are unavoidable in secondary
beams. Therefore wide acceptance is needed to collect a.larger amount of all the fragment. These angular andmomentum spread of the secondary beam are estimatedbased on the statistical model of Goldhaber[4].
Consequently the acceptance. values of ± 13mrad bothhorizontal and vertical angle, and ±2.S% in momentum
are chosen. With these values, the fragment separator cantransport as secondary beam, 6S% of He and 90% of
19Ne fragments produced in the reaction that a Scm-thickberyllium target are bombarded with 600MeV/nucleon
12(: and 2~e primary beams respectively.
Second order calculation An optics of an ion opticalsystem with a wide acceptance, might be affected by thehigher order aberration greatly. Hence we evaluated thesecond order aberration for the secondary beam course
using the code GIOS[5] and the following effects werefound. First, the focal plane at FO is slightly tilted
relative to the perpendicular plane to the optical axis.
Although this aberration deteriorates the momentum
resolution at FO, it was confirmed that degrading of theability is negligible for the separation of nuclei such as
11 C or 19Ne. Second, the image size is found to increase
owing to the second order aberration; especially at thefocusing points. As an example, the calculated position
distribution of the secondary beam of 11 C at the second
focus F1 is shown in Fig. 3. The secondary beam isassumed to be initially distributed of Gaussian shape inposition, angle and momentum space, whose widths aredetennined under the condition that the secondary beam is
produced by a bombardment of a primary beam of
600MeV/nucleon 12C with a Scm thickness beryllium
target. As shown in the figure, the second orderaberration does not make much difference to the position
distribution of the secondary beam, except for a rather
long outer tail. This tail may have a harmful effect forthe separation of the fragments with very small
production cross section from those with large production
cross section, but in most of case the effect is expteced tobe of little importance.

ACKNOWLEGEMENTS
The authors would like to thank Dr. K. Kawachi
for his encouragement and helpful advice.
REFERENCES[1] T. Kubo et. al., Nucl. Insr. and Meth. B70 (1992)

309[2] K. Sato et. al., Nucl. Phys. A588 (199S) 229c-234c[3] A. S. King et. al., SLAC-183-RL-7S-110 (1975)[4] A. S. Goldhaber, Phys. Lett. BS3 (1974) 306.
[S] H. Wollnik et al., Nucl. Instr. and Meth. A2S8(1987) 408.

1~~~~~~~~~~~--~~~~

f0 -10-S0S
Horizontal position (mm)10Fig. 3. Calculated u C beam position distribution at Fl.
Solid line : the second order caluculation
Dashed line : the first order calculation-412-