Kouichi Jimbo

A new Multiple Beams–Material Interaction Research Facility for radiation damage studies in fusion materials

Abstract As an important part of fusion materials research, evaluation of radiation damage in fusion materials has been emphasized more than two decades. Under the current situation with no 14 MeV neutron irradiation facility available for materials research, Multiple Beams–Materials Interaction Research Facility has to have a very important role in many years to come. In order to obtain clear understandings of radiation damage in fusion materials, as the dynamic material behavior under severe environments in advanced energy systems, such as fusion reactors, fission reactors, a Multiple Beams–Material Interaction Research Facility (DuET facility) has been constructed at the Institute of Advanced Energy, Kyoto University, in these three years. And is at the first stage of accelerator operation and adjusting. The facility consists of a 1.7 MV tandem accelerator system with a pair of ion sources (a cesium sputter type heavy ion source and a duo-plasmatron type light ion source), a 1.0 MV single-end accelerator system with a light ion source and three target stations. Some of the preliminary results utilizing HIT Facility, the University of Tokyo, is also provided with the future plan.

Negative ion current measurements with the modified JAERI probe

The modified JAERI probe, developed to measure negative hydrogen ion current, is a kind of Faraday cup with Nd magnets to distinguish negative ions from electrons. An extractable negative ion current is easily evaluated for extraction voltage less than 2 kV in the grounded negative ion source.

Efficiency Enhancement of Indirect Transverse Laser Cooling with Synchro-Betatron Resonant Coupling by Suppression of Beam Intensity

The efficiency of indirect transverse laser cooling with synchro-betatron resonance coupling has been improved with the reduction in beam intensity by scraping the tail part of the beam. In order to measure the beam size at a low beam intensity, a new scheme to measure the beam profile by observation of the survival ratio with changing the scraper position has been established. With 104 particles, the transverse cooling time was reduced to 1.2 s, and the cooled horizontal and vertical beam sizes were 0.19 and 0.61 mm, corresponding to temperatures of 20 and 29 K, respectively, which is largely improved compared with that in our previous experiment [Nakao et al.: Phys. Rev. ST Accel. Beam 15 (2012) 110102].

Features of the Uramoto‐type sheet plasma as a possible negative ion source

The Uramoto‐type sheet plasma, which has a unique magnetic field geometry, has been investigated with both Langmuir and JAERI probes [Rev. Sci. Instrum. 62, 772 (1991)]. In these investigations, the plasma potential was found to decrease while the extracted negative hydrogen ion currents increased in the cold region of the plasma. The extracted negative hydrogen ion current also increased as the plasma potential decreased at the same location when the chamber was biased more negative. These features are very favorable for negative ion generation since the destruction of negative hydrogen ions in the extraction region of the source can be minimized resulting in larger negative hydrogen ion currents at constant discharge power. An extracted negative hydrogen ion current density of 3 mA/cm2 was obtained in a 150 V–10 A discharge.

Improved confinement in the cold region of a Uramoto‐type ion source for negative hydrogen ion production

It has been reported that plasma confinement in the cold region of a Uramoto‐type sheet plasma ion source is very important for negative hydrogen ion production [Rev. Sci. Instrum. 66, 1035 (1995)]. In the present experiments, the stainless chamber was biased as low as 100 V relative to the anode potential in a 150 V–15 A discharge. The negative hydrogen ion current density (5 mA/cm2) was found to be larger than the positive hydrogen ion current density under the same experimental conditions. These experimental results suggest that the negative hydrogen ions are formed directly from atomic hydrogen.

Cavity Swelling Behavior in SiC/SiC Under Charged Particle Irradiation

Abstract The microstructural evolution of SiC/SiC composites after Si2+ with/without He+ ion irradiation was studied using transmission electron microscopy. The temperature, displacement damage level, and He/dpa ratio were 1273/1673K, 10/100dpa and 0/60appmHe/dpa, respectively. In 10dpa single-ion irradiation, no cavity was detected at 1273 and 1673K. But cavities were observed locally at 1673K, 100dpa. In dual-ion irradiation, cavities were observed at 1673K, 100dpa. Helium bubbles (d<5nm) were formed densely on {111} faulted planes in the fiber and matrix. And lens-shaped cavities (major axis 2a=20-50nm) were formed on grain boundaries in the matrix. The swelling by cavities in CVI matrix is about 0.5% at 80dpa and 0.7% at 130dpa. Loss of PyC layer beneath the irradiated surface was observed (single-ion: about 500nm, dual-ion: about 1 μm). And the thickness of the PyC layer expands after single/dual-ion irradiation (single-ion: 12%, dual-ion: 29% increase). But Tyranno-SA/PyC/CVI composites shows showed better microstructural stability than expected at 1673K.

Decay rate measurements in a negative ion rich plasma

By artificially terminating the hydrogen arc discharge in the sheet plasma experiments, the decay rates of the negative and the positive saturation currents of a Langmuir probe could be measured. This technique made it possible to observe, under a deep potential well geometry, two single decay curves of saturation currents, which decayed at the same rate reciprocally with time in the negative ion dominant cold region. This result illustrates that the negative saturation current, which consisted of chiefly electrons, was still proportional to negative ion density.