Norio Ogiwara

Application of the field emitter array to the vacuum measurements

We have successfully used the Spindt field emitter array (FEA) in the pressure measurements in ultrahigh vacuum (UHV) and extremely high vacuum (XHV). For applying the FEA to pressure measurements, we have made evaluation tests, focusing on gas exposure and outgassing characteristics. The cold cathode hardly influenced the vacuum conditions, compared to a hot-filament cathode.

Reduction of hydrogen content in pure Ti

Pure Ti is adopted as a material for ducts and bellows at the proton accelerator 3 GeV-RCS in J-PARC project, because of its small residual radioactivity. In the particle accelerator, the H2 outgassing due to ion impact is often the dominant source of gas release. As the reduction of hydrogen content will probably suppress ion induced desorption, we attempted to reduce the hydrogen content in the Ti by in-situ vacuum baking. First, thermal desorption behavior and the change in hydrogen content after the heat treatment were investigated. Vacuum firing at temperatures higher than 550°C was effective in reducing the hydrogen content in the Ti. At the same time, the mechanical properties were monitored because grain growth leads to decrease in mechanical strength. Even after treatment at 750°C for 12 hr, the decreases in tensile and yield strength were so small (~10%) that we have no anxiety about the reduction of mechanical strength. Based upon the results of this study, vacuum firing has been applied to reduce the hydrogen content in the Ti bellows and ducts of the RCS machine.

Titanium alloy as a potential low radioactivation vacuum material

For the vacuum systems of high-intensity beam accelerators, low radioactivation materials with good vacuum characteristics and high mechanical strength are required. The titanium alloy Ti-6Al-4V was investigated as a potential low activation vacuum material with high mechanical strength for the fabrication of vacuum components, particularly the flanges of beam pipes, in the J-PARC 3 GeV synchrotron. The dose rate of Ti-6Al-4V when irradiated by a 400 MeV proton was observed to decrease more rapidly than that of stainless steel. Furthermore, the generated radioactive isotopes were nuclides with relatively short half-lives. The outgassing rate per unit area of Ti-6Al-4V was approximately 10−8 Pa m3/s m2 after pumping for 100 h, which is the same as the typical value for stainless steel. Additionally, the hydrogen concentration in bulk Ti-6Al-4V was reduced to approximately 1 ppm by vacuum firing at 700 °C for 9 h; the mechanical strength was not reduced by this process. These results indicate that Ti-6Al-4V...

Electric Discharge Suppression by Outgassing Reduction from Kicker Magnet of J-PARC RCS

Kicker magnets in rapid cycling synchrotron (RCS) of Japan Proton Accelerator Research Complex (J-PARC) are now under construction. Extraction kicker magnets are short pulse magnets with high charging voltage of more then 60 kV which is installing in vacuum chambers. They mainly consist of aluminum alloy as electric plates and ferrites as magnetic cores. Outgassing reduction from those components is very important to prevent not only electrical discharge but also interaction between the proton beam and residual gas in the vacuum. Some structures of the magnet were improved to suppress discharge. We thoroughly reduced outgassing from the components. Surface of the aluminum alloy was finished by pit-free electropolishing. Aluminum alloy and ferrites cores were baked under vacuum before construction of the magnet. They were baked each other until water, which was the main component of outgassing, was reduced. As a result, outgassing rates of the aluminum alloy and ferrite cores were reduced less than 10-9 and 10 -10 Pa m/sec, respectively. We construct the system which is baked any time as needed by micro heaters directory mounted on the chambers