Takahiro Yamaki

Sputtering characteristics of B4C-overlaid graphite for keV energy deuterium ion irradiation

Two types of B 4 C-overlaid graphite (CFC), conversion and CVD B 4 C, together with bare CFC (PCC-2S) and/or HP B 4 C, were investigated with respect to erosion yields for 1 keV D + , D 2 /CD 4 TDS after 1 keV D + implantation, and thermal diffusivity/conductivity, in a temperature range from 300 to 1400 K. The erosion yields of both conversion and CVD B 4 C were found to be much lower than that of the bare CFC (PCC-2S), in both chemical sputtering (600–1100 K) and RES (1200–1400 K) temperature regions. The D 2 TDS peak of the conversion B 4 C was found to be located at nearly 200 K lower temperature than that of the bare CFC (PCC-2S), indicating much lower activation energy for detrapping/recombination of trapped D in the conversion B 4 C and in the CFC. The CD 4 TDS peak of the conversion B 4 C was found to be much weaker in intensity than that of the bare CFC (PCC-2S), in agreement with the present erosion yield results. Thermal diffusivities and conductivities of both the conversion B 4 C/PCC-2S and the CVD B 4 C, were measured to be nearly 1/10 of that of the bare CFC (PCC-2S), and to decrease with increasing temperatures.

Thermal desorption spectroscopy of boron/carbon films after keV deuterium irradiation

Abstract Thermal desorption spectroscopy (TDS) of D 2 and CD 4 was done on boron/carbon films (B/(B + C) = 0–74%), after 3 keV D + 3 irradiation to 4.5 × 10 17 D/cm 2 at 473 K. The D 2 desorption peaks were observed at 1050, 850 and 650 K. For a sputter B/C film (0%), only the 1050 K peak was observed. With increasing boron concentration to 3%, a sharp peak appeared at 850 K, the intensity of which was found to increase with increasing boron concentration to 23%, and then to decrease at 74%. The 650 K shoulder, which was observed for high boron concentration specimens, was speculated to be deuterium trapped by boron atoms in the boron clusters. The relative amount of CD 4 desorption was found to decrease with increasing boron concentration, which was attributed to the decrease in the trapped deuterium concentration in the implantation layer at temperatures at which CD 4 desorption proceeds.

New composite composed of boron carbide and carbon fiber with high thermal conductivity for first wall

Abstract A new composite was created from B 4 C powder and carbon fiber by hot-pressing at 1700°C or more. The composite sintered at 1700°C with 20–35 vol% B 4 C shows a thermal conductivity of 250 W/m·K at 25°C which is slightly lower than the felt type C/C, but its value becomes higher than the C/C at temperatures above 400°C. The composite with 40 at% B shows more controllable recycling properties than B 4 C. The erosion yield for the composite is about half the yield for graphite at 800 K. After electron beam irradiation in order to test heat resistance no cracks were detected up to 22–23 MW/m 2 leading to a surface temperature of 2500°C.

Erosion characteristics of B4C-converted CFC composite

Erosion characteristics of B 4 C converted CFC composite (conv-B 4 C) and bare CFC were investigated for 3 keV D 3 + , O + and Ne + irradiations in the 400-1400 K range. In both D + and O + irradiation cases, chemical sputtering observed for bare CFC was suppressed through B 4 C conversion. For D + irradiation to conv-B 4 C, the suppression of chemical sputtering was explained through a decrease in the trapped D density within the implantation layer around 700 K at which CD 4 desorption could take place. While as to O + irradiation to conv-B 4 C below 800 K, the suppression was explained through self-sputtering of trapped O atoms in place of target boron and carbon atoms

Thermal desorption spectroscopy of pyrolytic graphite cleavage faces after keV deuterium irradiation at 330–1000 K

Thermal desorption spectroscopy (TDS) measurements were made on D 2 and CD 4 from surface layers of pyrolytic graphite cleavage faces after 3 keV D 3 + irradiation to 1.5×10 18 D/cm 2 at irradiation temperatures from 330 to 1000 K. Thermal desorption of both D 2 and CD 4 was observed to rise simultaneously at around 700 K. The D 2 peak was found at T m = 900–1000 K, while the CD 4 peak appeared at a lower temperature, 800–840 K. The T m for the D 2 TDS increased, while that for the CD 4 decreased with increasing irradiation temperature. These results obviously indicate that the D 2 desorption is detrapping/recombination limited, while the CD 4 desorption is most likely to be diffusion limited. The amount of thermally desorbed D 2 after the D + irradiation was observed to monotonously decrease as the irradiation temperature was increased from 330 to 1000 K. These tendencies agreed with previous results for the irradiation temperature dependencies of both C 1s chemical shift (XPS) and the interlayer spacing, d 002 (HRTEM), on the graphite basal face.

New microwave ion source for plasma‐wall interaction studies

To obtain high‐flux hydrogen atoms equivalent to the irradiation condition at the surface of the first‐wall or divertor plate in a nuclear fusion reactor, a new microwave ion source was constructed and its operation was demonstrated. The source was designed so that H3+ ions are efficiently produced through the ion‐molecule reaction between H2+ ions and H2 molecules. Extracted ion beams were mass analyzed and pure H3+ ions were introduced into the ultrahigh‐vacuum target chamber. The obtainable irradiation current of H3+ ions was 1.5 mA at 3 keV. The beam diameter at the target was about 1 cm. Maximum flux density of hydrogen atoms at an energy of 1 keV exceeded 4×1016 H/cm2 s, which is high enough for plasma‐wall interaction studies.