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To resolve the drawback of conventional thyratron switches, development of a semiconductor high voltage switch utilizing a 13 kV class SiC-MOSFET developed by Tsukuba Power Electronics Constellations (TPEC) is proceeding. At first, the device evaluation test was carried out with a resistive load circuit. With the conditions of drain voltage of 10 kV and load resistance of 1 kΩ, turn on loss Eon, turn off loss Eoff, rise time Tr and fall time Tf were 1.7 mJ, 1.1 mJ, 64 ns, and 75 ns, respectively. Thereafter, the 2s-12p switch array was designed and assembled, where 12 MOSFETs are equally aligned on a circle shaped circuit board and two circuit boards are stacked in series. An 18 kV-318 A-1 us pulse with a rise time of 289 ns in the short pulse switching test were successfully demonstrated. Moreover, switching tests of 2nd generation MOSFET that has a twice larger device area was conducted. As a result, 60 % reduction of on-resistance was confirmed.

The linac-based neutron source “iBNCT” developed by the Tsukuba team has been shown to generate a large intensity of neutrons. To confirm the applicability of the device to BNCT, several characteristic measurements have been implemented. In a water phantom experiment, when the accelerator was operated with an average current of 1.4 mA, the maximum thermal neutron flux was approximately 7.8 × 108 (cm-2s-1). From estimation of the stability of the linac, the results demonstrate its applicability to actual treatment.

The linac-base neutron source “iBNCT” developed by the Tsukuba team has begun to generate a large intensity of neutrons. To confirm the applicability of the device to BNCT, several characteristic measurements have been implemented. In a water phantom experiment, when the accelerator was operated with an average current of 1.4 mA, the maximum thermal neutron flux was approximately 7.8 × 108 (n/cm2/s). Results demonstrate the stability of the linac over time, showing its promising potential for future patient treatment.

Boron neutron capture therapy (BNCT) is emerging as the next-generation radiation therapy, thanks to the recent technological advancements in the accelerator-based neutron source. In the iBNCT project headed by the University of Tsukuba, a linac-based BNCT device is being developed. The demonstrator of the iBNCT device commenced its operations in 2016. This paper reports the various experiments and measurements performed on the iBNCT device to confirm the physical characteristics of the neutron beam emitted from the beam aperture of the device. We evaluated the neutron energy spectrum at the beam aperture experimentally using the Bonner sphere detector method. The results demonstrated that the device emits the epithermal neutron beam corresponding with the energy spectrum assumed in the design phase. Furthermore, we performed experiments using a water phantom that simulates a human body whereby we measured the profiles of both thermal neutron flux and gamma-ray dose rate on the beam axis in the phantom. The results demonstrated that the iBNCT neutron beam has sufficient intensity applicable to clinical studies of the BNCT. In order to apply the iBNCT device to real-time therapy, we perform the device development on a continuous basis to further improve the stability performance as well as to increase proton current.

In boron neutron capture therapy, it is important to evaluate the dose administered to a patient's body outside the tumour area. The exposure dose is evaluated by calculation; however, the calculated value must be validated using a measured value. The dose evaluations based on the measured neutron spectrum are investigated. Multi-foil activation, combined with a LiCaAlF6 scintillation detector and an imaging plate, is proposed as a measurement method. The proposed method can measure the neutron spectrum at various points quickly.

All systems comprising the Japan Proton Accelerator Research Complex (J-PARC), namely, the 400 MeV linac, 3-GeV rapid-cycling synchrotron, and 50-GeV synchrotron, were completed in 2009 and are now being used to supply high-power proton beams to secondary particle users. In order to minimize maintenance and shorten the pump-down and conditioning period, an ultra-high vacuum of 10 −5 Pa or lower is required for the vacuum system. Here we present a review of the surface processing methods employed and the results of outgassing measurements for the components used in the vacuum system made from the following materials: electroformed copper, alumina ceramic, titanium, and stainless steel. The vacuum performance of these materials during accelerator operation is also reported.

Boron neutron capture therapy (BNCT) is one of the hopeful cancer therapies. Until recently, BNCT used the Nuclear fission reactor as a neutron source. However, many usable reactors for BNCT have been terminated and it is hard recently to build the new research reactor in many countries. Thus, a small accelerator which can supply the intense proton beam become a candidate of a neutron source instead of the reactor. Furthermore, it is impossible to install the reactor in a hospital but we can install the accelerator system in the hospital. In this article we describe the basic physics of the linear accelerator and cyclotron for BNCT. An ion source and the target for neutron production are also described briefly.

Clinical trials of the boron neutron capture therapy (BNCT) have been conducted using research reactors. Recent progresses in the accelerator and accelerator-driven-neutron-source technologies have rendered it possible to generate the substantial number of neutrons required for BNCT treatment, using a compact accelerator, which can be installed in a hospital. The University of Tsukuba launched a project for the development of a compact accelerator-based neutron source for BNCT. For this accelerator, we employed a linear particle accelerator (linac) and the energy of the proton beam was 8 MeV. Beryllium was selected as the neutron target material. To generate sufficient neutron intensity by the reaction between 8 MeV protons and beryllium, the linac accelerates a high current of 5 mA or more. As the target system is critical, we developed a beryllium target system with a threelayered structure to avoid target breakage, caused by massive heat load and blistering, within a short period. The linac-based neutron source for the BNCT is almost complete and we succeeded in generating neutrons, in 2015. Currently, several characteristic measurements are being carried out.

The HOM absorber for the normal conducting RF cavity of the KEK B-factory (KEKB) was designed. Sixteen bullet-shape sintered SiC (silicon carbide) ceramics are used for HOM absorption. The HOM power to be handled will be about 10 kW per cavity, corresponding to about 1 kW per absorber. A prototype of SiC absorber was made to verify the performance as a HOM absorber in vacuum. The high power test was carried out successfully using a pulsed klystron (f=1296 MHz). The design of the HOM absorber and the results of the high power test are discussed.

The input coupler for the normal conducting RF cavity of the KEK B-factory (KEKB) was designed comprising a disk-type coaxial ceramic window and a door-knob transition. We designed two different types of window structure; one is a choke-type structure and the other is a under- and over-cut structure. The fabrication of two types of coupler is underway in order to confirm the RF properties.