M. Muramatsu

Advanced RF-KO slow-extraction method for the reduction of spill ripple

Two advanced RF-knockout (RF-KO) slow-extraction methods have been developed at HIMAC in order to reduce the spill ripple for accurate heavy-ion cancer therapy: the dual frequency modulation (FM) method and the separated function method. As a result of simulations and experiments, it was verified that the spill ripple could be considerably reduced using these advanced methods, compared with the ordinary RF-KO method. The dual FM method and the separated function method bring about a low spill ripple within standard deviations of around 25% and of 15% during beam extraction within around 2 s, respectively, which are in good agreement with the simulation results.

Development of a compact electron-cyclotron-resonance ion source for high-energy carbon-ion therapy

Ion sources for medical facilities should have characteristics of easy maintenance, low electric power consumption, good stability, and long operation time without problems (one year or longer). For this, a 10GHz compact electron-cyclotron-resonance ion source with all-permanent magnets (Kei2 source) was developed. The maximum mirror magnetic fields on the beam axis are 0.59T at the extraction side and 0.87T at the gas-injection side, while the minimum B strength is 0.25T. These parameters have been optimized for the production of C4+ based on the experience at the 10GHz NIRS-ECR ion source and a previous prototype compact source (Kei source). The Kei2 source has a diameter of 320mm and a length of 295mm. The beam intensity of C4+ was obtained to be 530μA under an extraction voltage of 40kV. The beam stability was better than 6% at C4+ of 280μA during 90h with no adjustment of the operation parameters. The details of the design and beam tests of the source are described in this paper.

Performance of HIMAC

Abstract The NIRS heavy-ion two-synchrotron medical facility, HIMAC, was approved in the 1987 fiscal year and clinical trials were started in late June 1994 as previously arranged. The operation experiences show that the entire HIMAC facility can work well with high stability and excellent reproducibility. For example, the intensity of beam extracted slowly from the rings can be reduced as low as 500 particles per pulse because stable and reproducible acceleration can be achieved in the rings in spite of no beam feedback. This performance enables direct counting of the beam and its fragments in the preparatory experiments toward clinical treatments and provides a promising basis for acceleration and storage of radioactive beams toward simultaneous treatment and diagnosis in future.

Review on heavy ion radiotherapy facilities and related ion sources (invited)

Heavy ion radiotherapy awakens worldwide interest recently. The clinical results obtained by the Heavy Ion Medical Accelerator in Chiba at the National Institute of Radiological Sciences in Japan have clearly demonstrated the advantages of carbon ion radiotherapy. Presently, there are four facilities for heavy ion radiotherapy in operation, and several new facilities are under construction or being planned. The most common requests for ion sources are a long lifetime and good stability and reproducibility. Sufficient intensity has been achieved by electron cyclotron resonance ion sources at the present facilities.

Source of spill ripple in the RF-KO slow-extraction method with FM and AM

The RF-knockout (RF-KO) slow-extraction method with frequency modulation (FM) and amplitude modulation (AM) has brought high-accuracy irradiation to the treatment ofa cancer tumor moving with respiration, because ofa quick response to beam start/stop. However, a beam spill extracted from a synchrotron ring through RF-KO slowextraction has a huge ripple with a frequency of around 1 kHz related to the FM. The spill ripple will disturb the lateral dose distribution in the beam scanning methods. Thus, the source ofthe spill ripple has been investigated through experiments and simulations. There are two tune regions for the extraction process through the RF-KO method: the extraction region and the diffusion region. The particles in the extraction region can be extracted due to amplitude growth through the transverse RF field, only when its frequency matches with the tune in the extraction region. For a large chromaticity, however, the particles in the extraction region can be extracted through the synchrotron oscillation, even when the frequency does not match with the tune in the extraction region. Thus, the spill structure during one period ofthe FM strongly depends on the horizontal chromaticity. They are repeated with the repetition f of the FM, which is the very source ofthe spill ripple in the RF-KO method. r 2002 Elsevier Science B.V. All rights reserved.

Bio-Nano ECRIS: an electron cyclotron resonance ion source for new materials production.

We developed an electron cyclotron resonance ion source (ECRIS) for new materials production on nanoscale. Our main target is the endohedral fullerenes, which have potential in medical care, biotechnology, and nanotechnology. In particular, iron-encapsulated fullerene can be applied as a contrast material for magnetic resonance imaging or microwave heat therapy. Thus, our new ECRIS is named the Bio-Nano ECRIS. In this article, the recent progress of the development of the Bio-Nano ECRIS is reported: (i) iron ion beam production using induction heating oven and (ii) optimization of singly charged C(60) ion beam production.

Development of an ECR ion source for carbon therapy

A compact electron cyclotron resonance ion source has been developed for heavy-ion medical facilities. The beam intensity and stability were considerably improved by recent modifications on three points (length of sextupole, cooling system for the extraction electrode, and position of the Einzel lens). Initial results of C4+ beam tests show that an intensity of 180 eμA can be routinely obtained with simple tuning. The best record was 220 eμA for C4+, which meets the medical requirements. Throughout these tests, CH4 gas was used with 0.1 cc/min and the extraction voltage was fixed at 25 kV. Results on beam emittance and long-term stability are also briefly discussed.

Development of the National Institute of Radiological Sciences electron cyclotron resonance ion source for the heavy ion medical accelerator in Chiba

The development of an electron cyclotron resonance ion source for the heavy ion medical accelerator in Chiba (HIMAC) injector is reported. The HIMAC is a heavy ion medical accelerator for cancer therapy. The electron cyclotron resonance (ECR) ion source is expected to provide a long lifetime, easy operation, and easy maintenance for medical use. The NIRS‐ECR ion source has a single closed ECR stage, and a microwave frequency of 10 GHz is applied. Under the present performance, the output electrical currents of the ions are 2500 eμA for He1+, 300 eμA for C2+, 480 eμA for Ne3+, and 110 eμA for Ar6+. Stability of the intensity is better than 2%. The transmission efficiency through a low‐energy beam‐transport line with an acceptance of 200 πmm mrad is more than 70%; the typical 50% and 90% emittances of the injection beam with 8 keV/u are 20 and 80 πmm mrad, respectively. These performances satisfy the requirements for radiotherapy.

Status report on electron cyclotron resonance ion sources at the Heavy Ion Medical Accelerator in Chiba

The Heavy Ion Medical Accelerator in Chiba at the National Institute of Radiological Sciences (NIRS) is not only dedicated to cancer therapy, it is also utilized with various ion species for basic experiments of biomedical science, physics, chemistry, etc. Two electron cyclotron resonance (ECR) ion sources are installed for production of gaseous ions. One of them, the NIRS-ECR, is a 10 GHz ECR ion source, and is mainly operated to produce C4+ ions for daily clinical treatment. This source realizes good reproducibility and reliability and it is easily operated. The other source, the NIRS-HEC, is an 18 GHz ECR ion source that is expected to produce heavier ion species. The output ion currents of the NIRS-ECR and the NIRS-HEC are 430e μA for C4+ and 1.1e mA for Ar8+, respectively.

Fullerenes in electron cyclotron resonance ion sources

Fullerene plasmas and beams have been produced in our electron cyclotron resonance ion sources (ECRIS) originally designed for other purposes. The ATOMKI-ECRIS is a traditional ion source with solenoid mirror coils to generate highly charged ions. The variable frequencies NIRS-KEI-1 and NIRS-KEI-2 are ECR ion sources built from permanent magnets and specialized for the production of carbon beams. The paper summarizes the experiments and results obtained by these facilities with fullerenes. Continuous effort has been made to get the highest C60 beam intensities. Surprisingly, the best result was obtained by moving the C60 oven deep inside the plasma chamber, very close to the resonance zone. Record intensity singly and doubly charged fullerene beams were obtained (600 and 1600nA, respectively) at lower C60 material consumption. Fullerene derivatives were also produced. We mixed fullerenes with other plasmas (N, Fe) with the aim of making new materials. Nitrogen encapsulated fullerenes (mass: 720+14=734) we...