The 9th Symposium on Accelerator Science and Technology, Tsukuba, Japan 1993

Present Status of NIRS Medical Accelerator - HIMAC
K. Sato, A. Itano, M. Endo, H. Ogawa, T. Kanai, M. Kanazawa, K. Kawachi, A. Kitagawa, M. Kumada,H. Koyama-Ito, T. Kohno, Y. Sato, M. Sudou, F. Soga, E. Takada, H. Tomura, K. Noda, Y. Furusawa,S. Minohara, N. Miyahara, T. Murakami, S. Yamada, J. Yoshizawa, and Y. Hirao

Research Center of Charged Particle Therapy
National Institute of Radiological Sciences
4-9-1, Anagawa, Inage-ku, Chiba 263, Japan
Abstract
The NIRS heavy-ion medical accelerator facility,HIMAC, is corning to the final construction stage. Allelements of the accelerator system were delivered. Successful
beam acceleration test of the injector linac system and thus
its commissioning is one of the most important ·progress in
the last one and a half year. The elements of synchrotrons,
high-energy beam transport lines, and irradiation equipments
are accurately aligned and are under operation tests at theinstitute extensively toward completion by the end of thisyear, 1993.
This paper briefly describes a present status of theHIMAC facility at the middle of the year. The feature offield control of lattice magnets of the synchrotrons is
discussed as another sample of the progress since the lastsymposium.
Introduction
Heavy-Ion Medical Accelerator in Chiba (HIMAC) at
National Institute of Radiological Sciences (NIRS) is
dedicated to heavy-ion cancer therapy and is the first heavyion medical accelerator facility in the world. The accelerator
is capable of variable particle, variable energy, and variable
intensity to satisfy medical requirement such as a longresidual range of 30 em in human bodies and a high dose
rate of 5 G/min at therapy rooms. In addition, stable andreproducible operation is strongly required for the medicaluse.
The HIMAC facility is divided into four systems. Main
accelerator is two identical synchrotron rings installed at
upper and lower underground floors of the building. Injector
accelerator is a cascade of an RFQ linac and an Alvarez
linac preceded by two kinds of ion sources, a PIG source
and an ECR source. High-energy beam transport system
consists of vertical and horizontal beam lines which deliver
the beam from the upper and lower rings to three treatment
rooms and experimental irradiation rooms. One of threetherapy rooms is equipped with simultaneous vertical andhorizontal beam irradiation port, while the others areequipped with vertical only and horizontal only, respectively.
Since HIMAC had been approved by the Government
in 1987 as a seven year project, contracts with companies forfabrication and delivery of accelerator elements of eachsystem have been made from 1987 to 1991. Construction
works for the building including associated facility such as
power substation and air-conditioning system have been
contracted from 1987 to 1993 through the regional office of
the Construction Ministry and is to be completed in themiddle of 1993. While Mitsubishi Electric Corp. became themain contractor of the accelerator construction, thearrangement is such that Sumitomo Heavy Industries, Ud.
took charge for the injector linac system, and that Hitachi
Ltd. and Toshiba Corp. shared the responsibility for thesynchrotron system. Mitsubishi Electric Corp .. herself wasassigned for the high-energy beam transport system, theirradiation system, and water-cooling system for theEach company further called various subaccelerators.
contractors to meet the state-of-the art specification of many
In addition, a new company,devices and techniques.
Accelerator Engineering Corp., has joined in the last year for
operation and maintenance of the HIMAC facility. The final
contract for installation, operation tests at the institute, andbeam tuning is made in 1992 and 1993 aiming at completionof the HIMAC facility in the 1993 fiscal year.
The delivery of the injector system had started in theearly part of 1992 and the other system in the middle of thesame year, respectively.
Present status of the HIMAC facility
In Fig. 1(a) to 1(i), recent photographs of significant
elements of each system are collected together with aschematic bird's eye view of the whole facility.
As of July, 1993, all construction works of the building
and the accelerators are nearing to the final stage. The
building is being reviewed for inspection and a final civilengineering work is underway as seen from Fig. 1(i).
Beam acceleration test of the injector linac system wascarried out this spring with satisfactory results(1 ], which isdiscussed later. Concerning the other systems, elements arebeing installed and are under operation tests without beam.
In the case of the synchrotrons, the accuratealignment(2] of elements such as magnets, beam monitors,
and electrostatic inflector and deflectors has· been completed
and vacuum ducts for them have been assembled as shownin Fig. 1(e). At present, all vacuum components of thelower ring are being baked out at 2000C for high vacuum[3].
On the other hand, preliminary tests on power supplies forring dipole magnets and quadrupole magnets have started
although a bridging bypass resistor for a magnet coil(4] will
be equipped later very soon. In addition, on-site tests of acomputer control system[5] are being made. At the end of
this year, the beam from the injector linac will be transferredto the synchrotrons.
In the case of the high-energy beam transport system,
it was already at the checking stage of major magnet power
supplies for the system in early 1992. Those power supplies
showed satisfactory stability for 8 hour run at a manufacturer.
Vacuum system was also extensively checked and sequencecontrol of turbo molecular pump sets was adjusted. Most of
the beam line elements including profile monitors weredelivered in the last year and were aligned subsequently.
Alignement of the vertical beam lines has been completedrecently.
For the treatment and irradiation system, the wobbler
magnets and their power supplies were tested and installed.
Several devices for beam collimation and range modulationsuch as ridge filters, range shifters, block collimators, andmulti-leaf collimators were also delivered and aligned.
The global interlock system and supervisory computer
have been installed and connection to each subsystem isbeing examined.
The building has been constructed from year to year forthe reason of the budget based on the scheduled contracts as
described above. Movement of the building[2], however, wasunavoidable during a period for initial installation andaccurate alignment because there was no enough time
between the construction of the building and the installationof the accelerator elements. Main component seems to besuch uniform movement as rolling and pitching of thebuilding as a whole. Detectable movement seems to occur
within one month or so. The accurate alignment of theaccelerator elements is being extensively made in as shortperiod as possible in order to overcome this problem.
In the following, two topics will be highlighted to show
the recent result of the HIMAC accelerators.

-20-Fig. l

Schematic bird's eye viewand recent photograghs ofHIMAC facility(a) Schematic bird's eye view(b) Ion sources:
ECR(front) & PIG(rear)(c) Injector linac cascade:RFQ(front) & Alvarez(rear)(d) Injection beam line:
Switching mag. for both rings(e) Lower synchrotron:
BM+QM(front) & RF(rear)(f) High-energy beam line:
Horizontal beam line(g) Irradiaiton device: Wobbler mag.
(h) Therapy room:
Vertical line to be installed(i) Building(d)'......
-'=>

(i)

(e)

(f)

(h)

Commissioning of the injector linac system
The injector linacs had been once assembled accurately
at the company and were powered successfully without beam
acceleration. The linacs were then appropriately divided into
several tanks for shipping, each of which was delivered tothe institute. Because elements such as vanes of the RFQ
linac and drift tubes of the Alvarez linac were kept at proper
positions for shipping, . main works after the delivery werecareful joint between the tanks and accurate installation as awhole of the each linac. In addition, because a period forinstallation and alignment was rather short, the movement of
the building, which is described above, did not affect onthese works. Figures 1(b) and 1(c) show photographs of theion sources and the cascade of the RFQ linac and theAlvarez linac, respectively, after completion of installation inFebruary, 1993.
As soon as the electric power substation and the watercooling system had become available, operation tests of theMulti-pactoring due to rf power
linacs have started.
excitation was easily overcome. Ion species for the firstbeam was chosen to be He'• ions because of lower rf power
level and enough intensity produced at the ion source incomparison to those of ions with a charge to mass ratio of1(7. The acceleration tests have finished very soon because
Such performance of the beamof no major trouble.
acceleration for 6 MeV/u by the linac cascade as transmission
efficiency of about 90 %, beam intensity of 800 e 11 A, andnormalized emittance of 1 n •mm•mrad is proven to bealmost same as design values. This success leads us thecommissioning of the injector linac system very quickly.
Field control of synchrotron magnets
Field distribution of lattice dipole and quadrupole
magnets had been extensively computed in 2-dimensional
calculation during the design period. Cross section of themagnets are then manufactured on the basis of thecomputations. Performance of the magnets, however, is muchaffected by leakage field around pole ends along the beam
direction. In order to realize the nice overall performance ofmagnets, we have attached adjustable and demountable end
pieces for both dipoles and quadrupoles. In the case of thedipoles, the end pieces are adjusted in thickness to achieve
the same product of field strength and effective length, BL,
just on the beam axis for all dipoles of the ring. In the caseof the quadrupoles, the end pieces are adjusted in shape toachieve the uniform radial and vertical distribution of a
product of field gradient and effective field length, GL(x) andGL(y).
The product BL on the beam axis of the dipoles is once
normalized at a field strength of 1 T experimentally bymeans of thickness adjustment of the end pieces in measuring
a deviation of BL from the reference magnet. Measured dataof deviation of BL at low and high field strength are thenplotted in a two-dimensional figure: for example, a horizontal
axis for deviation at the low field and a vertical axis for thatat the high field. It is noticed from the figure that thedeviations at low and high strengths have a correlation thatthe data for many magnets tend to fall on a straight line. It
is considered from a natural extension of Ampere's law thata lower remanent field results in a higher permeability andvice versa due to the characteristics of ferromagnetic materialof magnet core. This analysis has been very helpful toconfirm a validity of the field measurement because
erromeous data is away from the line largely.
In addition, the relation between the deviations at thelow and high fields is applied to decrease a closed orbit
distortion in wide dynamic range of the field strength on thebasis of appropriate shuffling of the magnets, because the all
magnets are normalized at 1 T in BL and deviations at low
and high fileds have opposite values.
A new expression for fitting between a field strengthand a coil current is proposed to be a sum of two inverse
polynomials as a natural extension of Ampere's law, too. It
is featured that most of all parameters in the expression
correspond to physical quantity of the magnets such as aremanent field and a magnet gap. A preliminary fitting
result based on the 4th order polynomials shows anagreement in the observed value of a remanent field and thedesign value of a magnet gap. Consequently, it is confirmed
from the agreement that fabrication of the magnets and fieldmeasurement including measurement of coil excitation current
are valid.
Radial and vertical distribution of GL(x) and GL(y) of
the quadrupoles is adjusted extensively in a given boundary
condition of the end pieces to achieve as uniformity
independent of coil current as possible. In order to control
the distribution easily, a nice method has been found[6]. The
end pieces consist of stacked sheets and are finally glued fora solid block. The end pieces were originally shaped in a
regular step with a given width of tread on the basis of an
appropriate straight line. We have observed the effect ofsheets of each step on distribution of the GL product toincrease or decrease the sheets. Combining the effect ofeach step, we have achieved a nice distribution.
Summary
All elements for the HIMAC accelerators have beentested at the companies to confirm the performance before
delivery to the institute. For examples, such measurement as
field distribution and excitation curve have been made formagnets, operation tests for actual or dummy loads have been
made for power supplies, and operation tests such as rf
power excitation have been made for devices such as rfaccelerating cavities. These measurements and tests haveshown the performance that meets the specification. Special
procedure such as field control of the dipoles and thequadrupoles has been newly developed during this period formeasurements and tests.
Presently the HIMAC accelerator facility is coming to
the final construction stage of the seven year project which
had been approved in 1987. Commissioning of the injector
linacs has been made recently. Elements of the other systemwere delivered, are being aligned accurately, and are undertests one after the others extensively to aim at beam transferfrom the injector linac to the synchrotron in the later part of1993.
Acknowledgement
There are so many works for the entire HIMAC facility.
In particular, all elements should be manufactured precisely,aligned accurately, and tested carefully by very many persons
in order to satisfy the specification. The authors are muchindebted to them for efforts toward the completion in the1993 fiscal year. Staffs of the institute, guest scientists, andengineers of many companies concerning the HIMAC project
are greatly acknowledged.
References[1] T. Murakami et al., Beam Test of HIMAC Injector,
contribution to this symposium (PA12)[2] K Sato et a!., Accurate Geodetical Settlement ofReference Points for HIMAC Synchrotrons at NIRS,ibid. (PB9)[3] M. Kanazawa et al., Vaccum System for HIMAC
Synchrotrons, ibid. (PASS)[4] M. Kumada et al., Analysis of the HIMAC Synchrotron
Power Supply, ibid. (DL4)[5] E. Takada et al., Synchrotron Control System of theHIMAC, ibid. (PA16)[6] A. Itano et al., Field Measurement and End Shim Controlof the HIMAC Quadrupole Magnet, ibid. (PB13)-22-