Facilities

HIMAC (Heavy-Ion Medical Accelerator in Chiba)

HIMAC, a heavy-ion synchrotron for medical use, began its operation in November, 1993. An aim of HIMAC is to evaluate the therapeutic advantages of heavy-ion beams for cancer therapy. The accelerator was, thus, designed to fulfill the medical requirements listed in Table 1.


       Table 1  Medical requrements
------------------------------------------------
  Particle species     He,C,Ne,Si,Ar
  Penetrating range    30cm in tissue
  Dose rate            5Gy/min.
  Max. field size      22cm in diameter
  Beam direction       Vertical and horizontal
------------------------------------------------

HIMAC comprises ion sources, injector, a synchrotron, a beam-transport system, three clinical treatment rooms, and four experimental rooms, an outline of the accelerators is summarized in Table 2.


        Table 2  Outline of the accelerators
----------------------------------------------------------
  Ion source
    PIG and ECR           8keV/nucleon
  Injector
    RFQ linac             800keV/nucleon
    (0.6m¦Х * 7.3ml)      (4% of the light velocity)
    Alvarez linac         6MeV/nucleon
    (2.2m¦Х * 24ml)       (11% of the light velocity)
  Main accelerator
    Synchrotron           100-800MeV/nucleon
    (42m¦Х)               (43-84% of the light velocity)

  Treatment rooms
    3 treatment rooms
    4 experimental rooms
----------------------------------------------------------

The ion sources produce ions (tiny charged particles) by stripping electrons from atoms in various forms: gas or solid. The sources are placed on platforms to which a high voltage of 60kV (static electric field) can be applied. Extracted ions are pre-accelerated by a high voltage and injected into the accelerators. Two types of ion sources have been installed: PIG (Penning ionization gauge) and ECR (electron cyclotron resonance).

The injector comprises two types of linear accelerators: an RFQ linac (1st stage) and an Alvarez linac (2nd stage). The linear accelerators use an RF electromagnetic field of 100MHz with a high power of ЎБ0.8 MW for accelerating beams. A combination of two types of linaces increases the energies of heavy-ion beams up to 6Mev/nucleon, corresponding to 11% of the velocity of light. At the exit of the injector, the ions are fully stripped (no electrons around the nuclei) after passing through a thin carbon foil. (Many electrons move around the nuclei in heavy atoms, and not all electrons can be removed in ion sources.) The beams are then transported to the synchrotron.

A synchrotron is a complex system comprising bending magnets, quadrupole magnets, an accelerating RF cavity, vacuum ducts, etc. located in a circular from(ring), Injected beams circulate in the ring on the order of 100000 times (ЎБ0.4 sec), while gradually increasing their energy. The final energies vary from 100 to 800 MeV/u, depending on the required ranges. The maximum velocity reaches as high as 84% of the velocity of light. The HIMAC synchrotron comprises two identical rings: upper and lower. The two-ring structure enhances the utility of the accelerator because they can deliver beams to two treatment courses simultaneously. Fully accelerated heavy ion beams are tranported using a high-energy beam-transport system (combination of many magnets and a beam-monitoring system).

Three clinical treatment rooms have been prepare. Since the size and volume of cancer varies greatly, the beam shape and energy must be different from patient. The treatment rooms are thus equipped with beam-shaping devices: wobbler magnets, a ridge filter, a multileaf collimator, a range shifter, etc. A wide range of basic experiments, on the other hand, can be carried out in four experimental rooms; there are rooms for (1) biological experiments, (2) generalpurpose, and (3) secondary-beam experiments, and (4) medium-energy experiments.

[Fig. 1] [Fig.1] Bird's eye view of the HIMAC facility.
large size image is here. (44 kbyte)

[Fig. 2] [Fig.2] RFQ and alvarez linacs.

[Fig. 3] [Fig.3] Synchrotron.

[Fig. 4] [Fig.4] High-energy beam-transport system.

[Fig. 5] [Fig.5] Treatment room.

Home Page

Facilities