Akinori Sugiura

Status of ion sources at National Institute of Radiological Sciences

The National Institute of Radiological Sciences (NIRS) maintains various ion accelerators in order to study the effects of radiation of the human body and medical uses of radiation. Two electrostatic tandem accelerators and three cyclotrons delivered by commercial companies have offered various life science tools; these include proton-induced x-ray emission analysis (PIXE), micro beam irradiation, neutron exposure, and radioisotope tracers and probes. A duoplasmatron, a multicusp ion source, a penning ion source (PIG), and an electron cyclotron resonance ion source (ECRIS) are in operation for these purposes. The Heavy-Ion Medical Accelerator in Chiba (HIMAC) is an accelerator complex for heavy-ion radiotherapy, fully developed by NIRS. HIMAC is utilized not only for daily treatment with the carbon beam but also for fundamental experiments. Several ECRISs and a PIG at HIMAC satisfy various research and clinical requirements.

Development of gas pulsing system for electron cyclotron resonance ion source

A gas-pulsing system for an electron cyclotron resonance ion source with all permanent magnets (Kei2 source) at NIRS has been developed and tested. The system consists of a small vessel (30 ml) to reserve CH(4) gas and two fast solenoid valves that are installed at both sides of the vessel. They are connected to each other and to the Kei2 source by using a stainless-steel pipe (4 mm inner diameter), where the length of the pipe from the valve to the source is 60 cm and the conductance is 1.2 l/s. From the results of the test, almost 300 e microA for a pulsed (12)C(4+) beam was obtained at a Faraday cup in an extraction-beam channel with a pressure range of 4000 Pa in the vessel. At this time, the valve has an open time of 10 ms and the delay time between the valve open time and the application of microwave power is 100 ms. In experiments, the conversion efficiency for input CH(4) molecules to the quantity of extracted (12)C(4+) ions in one beam pulse was found to be around 3% and the ratio of the total amount of the gas requirement was only 10% compared with the case of continuous gas provided in 3.3 s of repetition in HIMAC.

Status of ion sources at the national institutes for quantum and radiological science and technology (QST)

The National Institutes for Quantum and Radiological Science and Technology (QST) manages various types of ion sources for research and development in the fields of life sciences, medical and industrial applications, and fusion energy science. The QST is currently developing on electron cyclotron resonance ion sources, negative ion sources (ion sources for fusion and for tandem accelerators), ion sources for radioactive beams, laser ion sources, and miscellaneous ion sources. Its intra- and inter-institutional collaborations make QST a promising platform for future ion source technologies.The National Institutes for Quantum and Radiological Science and Technology (QST) manages various types of ion sources for research and development in the fields of life sciences, medical and industrial applications, and fusion energy science. The QST is currently developing on electron cyclotron resonance ion sources, negative ion sources (ion sources for fusion and for tandem accelerators), ion sources for radioactive beams, laser ion sources, and miscellaneous ion sources. Its intra- and inter-institutional collaborations make QST a promising platform for future ion source technologies.

Improvement of the NIRS-930 Cyclotron for Targeted Radionuclide Therapy

In recent years, the production of radionuclides for Targeted Radionuclide Therapy (TRT) with the NIRS-930 cyclotron has been one of the most important activities in National Institutes for Quantum and Radiological Science and Technology (QST, NIRS). In the production of At, for example, a target material with low melting point is irradiated with a high intensity helium ion beam. A vertical beam line has the advantage in irradiation with low-melting-point target. Therefore, a vertical beam line has been modified for the production of radionuclides. This line was used for neutron source with beryllium target. The beam intensity and beam energy are important parameters for the effective production of radionuclides for TRT. In order to increase beam intensity, the acceleration phase and injection energy have been optimized by measuring beam phase. The beam energy has been measured by TOF and adjusted by tuning the acceleration frequency. Those studies and improvement are reported.

Status of a compact electron cyclotron resonance ion source for National Institute of Radiological Sciences-930 cyclotron.

The Kei-source is a compact electron cyclotron resonance ion source using only permanent magnets and a frequency of 10 GHz. It was developed at the National Institute of Radiological Sciences (NIRS) for producing C(4+) ions oriented for high-energy carbon therapy. It has also been used as an ion source for the NIRS-930 cyclotron. Its microwave band region for the traveling-wave-tube amplifier and maximum output power are 8-10 GHz and 350 W, respectively. Since 2006, it has provided various ion beams such as proton, deuteron, carbon, oxygen, and neon with sufficient intensity (200 μA for proton and deuteron, 50 μA for C(4+), for example) and good stability for radioisotope production, tests of radiation damage, and basic research experiments. Its horizontal and vertical emittances were measured using a screen monitor and waist-scan. The present paper reports the current status of the Kei-source.

Beam Simulation for Improved Operation of Cyclotron NIRS-930

A beam inside NIRS-930 cyclotron (Thomson-CSF, Kb=110 MeV, Kf=90 MeV) is diagnosed by such device as differential prove and phase prove, though the beam behavior is not well recognized. To understand the behavior of the beam, beam simulation is an effective method. The SNOP code is developed to simulate multiple particles in a cyclotron taking account of space charge effect using PIC method. Firstly, comparing the simulation results with actual measurement, we can ensure the correctness of simulation. The phase variation of 18 MeV proton beam of simulation was compared to that of the experiment. Both results show similar tendency. The beam loss point was also studied in simulation changing beam injected phase. We found that a lot of particles injected with early phase are lost at deflector. On the other hand, a lot of particles injected delayed phase is lost at inflector. The difference of the phase of maximum transmission ratio at inflector and deflector was 20°. Furthermore, space charge effect was found to decrease transmission efficiency if the injection beam current is more than ~1 mA. Considering the results of the simulation, actual operation of the NIRS-930 cyclotron can be improved.

Broadband “in-series multistation” rf cavity with low voltage standing wave ratio

A configuration for an untuned broadband rf cavity with a low-voltage standing wave ratio (VSWR) is proposed. Although an untuned broadband cavity is currently implemented by loading magnetic alloy (MA) cores, the VSWR of such a cavity is expected to be no less than approximately 2.0 in the operational frequencies sweeping by a factor of about 10. A type of rf cavity, “in-series multistation” cavity, described here can cover a much broader frequency range sweeping by a factor of 20, while keeping the VSWR value below 1.2. The system consists of multiple stations, each of which is loaded with low-Q high-permeability MA cores. A “bench” test circuit was built and successfully tested.