The first (Phase-1) commissioning of SuperKEKB, an asymmetric-energy electron-positron collider at KEK, began in February 2016, after more than 5 years of upgrade work on KEKB and successfully ended in June 2016. A major task of the Phase-1 commissioning was the vacuum scrubbing of new beam pipes in anticipation of a sufficiently long beam lifetime in the next commissioning. The pressure rise per unit beam current decreased steadily with increasing beam dose, as expected. Another important task was to check the stabilities of various new vacuum components at high beam currents of approximately 1 A. The temperature increases of the bellows chambers, gate valves, connection flanges, and so on were less than several degrees at 1 A, and no serious problems were found. The effectiveness of the antechambers and TiN coating in suppressing the electron-cloud effect (ECE) in the positron ring was also confirmed. However, the ECE in the Al-alloy bellows chambers was observed where TiN had not been coated. The use of permanent magnets with an axial magnetic field of approximately 100 G successfully suppressed this effect. Pressure bursts accompanying beam losses were also frequently observed in the positron ring. The preparation for the next Phase-2 commissioning, such as the installations of new beam pipes at the collision point and of six more beam collimators, are now in progress.
The stability of the output of a pressure sensor using a temperature-stable quartz oscillator for outdoor use was improved. This was accomplished by reducing the temperature change in the preamp of the pressure sensor using a thermal insulation bag for the preamp. The thermal insulation bag reduced the change in temperature at the preamp by approximately several degrees centigrade. Thus, fluctuations in the output from the pressure sensor were suppressed, with increasing average atmospheric temperature. The method used in this study was less effective at lower atmospheric temperatures, probably because of the preamp temperature dependence of the pressure sensor output. It can be concluded that the method used in this study is not sufficiently effective at all atmospheric temperatures to reduce fluctuations in the output from the pressure sensor below 0.33%, which is the necessary level for practical use of a hydrogen sensor in outdoor environments.
Ellipsometry monitoring was carried out in-situ for the analyses of substrate surface in the first stages of graphene growth in magnetron plasma-enhanced chemical vapor deposition. By the comparison of the experimentally obtained trajectory of ellipsometric parameters on the Ψ-Δ coordinate plane to that of the calculated ones, it has been found that graphene tends to grow parallel to substrate surface under the pressure of 10 Pa while perpendicularly under that of 200 Pa.
We have developed a portable ultrahigh-vacuum sample transfer vessel. The size of the vessel is about 55 cm in length, and 5.2 kg in weight. The lowest vacuum pressure achieved by this device was ∼8×10−7 Pa. It is improved by 1/6, compared to the previous device. The transfer vessel was used for analysis of DNA thin film.
A model gas separator that makes use of the molecular exchange flow through porous membrane of 18 cm2 area is fabricated. The effect of molecular exchange flow is accumulated by the counter flow of gas mixture that flows around the membrane. The half part of the device concentrates light molecules, and the other concentrates heavy molecules. This study demonstrates the capability of the device to make two flows of different gases whose difference of mole percentage is around 6.5% from a continuous feed flow of 3 sccm helium-neon 50% mixture. The effect of the product flow rate and the flow rate around the membrane are also investigated.
This paper describes the microfabrication of titanium micro molds for the microfluidic chip by a reactive ion etching (RIE) system. The etching was carried out using SF6 plasma. We have examined the etching rate and surface roughness at the range of process pressure 0.3-0.7 Pa and RF (13.56 MHz radio-frequency) power 30-70 W. The etching rate is over 0.3 μm/min at the RF power of 70 W. The surface roughness of etched substrates is below 40 nm at the process pressure of 0.3 Pa. We made a titanium micro mold and molded microfluidic chips by using polycarbonate, and microresico® (Polypropylene resin).
We propose a simple method to fabricate SiO2 diaphragms supported on a Si substrate by using the inward plasma etching. In this method, a Si substrate covered with SiO2 was locally etched with the inward plasma from the Si side. When using a SiO2 (280 nm)/Si (380 μm) substrate, a SiO2 diaphragm with a diameter of ∼50 μm was fabricated at the bottom of the bowl-like hole with an opening diameter of ∼1.2 mm. This method does not require lithographic processes which are inevitable for the conventional microfabrication techniques and may be used to fabricate MEMS devices in the lab.
To observe specular oscillations in ion-surface scattering originating from layer-by-layer desorption of an electron stimulated desorbed (ESD) surface, a 15 keV proton beam was impinged on the surface with an angle of incidence less than 1°. We prepared an experimental system to examine the scattering yields of reflecting protons by conveniently employing a fluorescent screen to view scattering yields (scattering patterns) and a commercial digital camera for yield measurements. Because the present energy of the proton beam was too low to illuminate the screen, a micro-channel plate was inserted in front of the screen. Measurements with electron irradiation show obvious damping specular oscillations; the widths of angular distributions of scattered protons simultaneously oscillated with increasing electron fluence. From the measured periods of the oscillations, the ESD rates of thermal desorption from KBr(001) at 1.5 keV electrons irradiation were obtained for sample temperatures.