Hitoshi Akimichi

Two-stage flow-dividing system for the calibration of vacuum gauges

A two-stage flow-dividing system was developed for calibrating an ionization gauge (IG) and residual gas analyzer (RGA). This system generates a stable high and ultrahigh vacuum from 8×10−3to2×10−7Pa by adjusting the pressure in the first chamber using N2, Ar, He, and H2. The calibration pressure in the third chamber is calculated from the pressure in the second chamber using their linear relation in molecular flow. The uncertainty of the generated pressure was comparable to or several times larger than that of the continuous-expansion system. However, this system has a simple configuration and is easy to operate compared with the continuous-expansion system because it has no moving parts. Results of the calibration of IG and RGA showed that the two-stage flow-dividing system is useful for a routine calibration of practical vacuum gauges in high and ultrahigh vacuum.A two-stage flow-dividing system was developed for calibrating an ionization gauge (IG) and residual gas analyzer (RGA). This system generates a stable high and ultrahigh vacuum from 8×10−3to2×10−7Pa by adjusting the pressure in the first chamber using N2, Ar, He, and H2. The calibration pressure in the third chamber is calculated from the pressure in the second chamber using their linear relation in molecular flow. The uncertainty of the generated pressure was comparable to or several times larger than that of the continuous-expansion system. However, this system has a simple configuration and is easy to operate compared with the continuous-expansion system because it has no moving parts. Results of the calibration of IG and RGA showed that the two-stage flow-dividing system is useful for a routine calibration of practical vacuum gauges in high and ultrahigh vacuum.

Effect of surface material and roughness on conductance of channel between parallel disks at molecular flow

The effect of surface material and roughness on the conductance of a channel at molecular flow was measured for N2, Ar, He, and H2. The experimental results were compared with the results of Monte Carlo calculations. The channel consisted of two parallel disks with different surfaces including polished stainless steel (SS), roughly polished SS, quartz, Ti, Cu, Al, alumina with smooth surface, alumina with rough surface, Au coating, Pt coating, and diamondlike carbon (DLC) coating. The conductances of the experimental channel depended on the slope of the surface roughness, rather than the arithmetic surface roughness (Ra) or the material. In the case of smooth surfaces, such as polished SS, quartz, and DLC coating, the experimental results for N2, Ar, and H2 show good agreement with the calculation, assuming diffuse reflection. The momentum accommodation coefficients on these surfaces for N2, Ar, and H2 were estimated to be in the range from 0.98 to 1.00, based on the assumption that specular reflection wa...

Generation of precise micro gas flows by a constant pressure flowmeter

Micro He gas flows ranging from 10-7 to 10-5 Pa m3/s are generated by a constant pressure flowmeter with an uncertainties of 1.1~0.91%, when the pressure in the flowmeter is changed from 1 to 100 Pa. Holding a pressure in the flowmeter during an operation of this type of the flowmeter is one of the important parameters to generate precise and stabilized gas flow rates. By controlling the volume reduction rate based on the proportional-integral-derivative (PID) algorithm, a relative fluctuation ratio of the pressure is kept within 0.03% above the pressure of 1 Pa

Generation of a stable vacuum pressure by flow method using micro capillaries

A stable vacuum pressure is necessary to calibrate a vacuum gauge by direct comparison. Three flow methods to generate a vacuum pressure are examined; by using a variable leak valve, a mass flow controller and a micro capillary in conjunction with a precise pressure controller for the calibration of a spinning rotor gauge. The fluctuation of generated pressure by using a micro capillary in conjunction with a pressure controller is 0.01%-0.22%, that is the most stable of three methods, and the adjustable pressure range is more than 4 orders, from 3times10-4 Pa to 5 Pa. The two-stage flow method using two capillaries in series is also examined to generate a stable ultra-high vacuum (UHV) pressure for the calibration of an ionization gauge. The fluctuation of generated UHV pressure lies within the range from 0.1% to 0.6% corresponding to the pressure from 2times10-7 Pa to 6times10-3 Pa. The fluctuations are mainly determined by the resolution of the digital indication of the ionization gauge