| AVS 59th Annual International Symposium and Exhibition | |
| Vacuum Technology | Monday Sessions |
| Session VT-MoA |
| Session: | Gas Flow, Leaks, Permeation and Mass Analysis |
| Presenter: | H. Yoshida, National Institute of AIST, Japan |
| Authors: | H. Yoshida, National Institute of AIST, Japan K. Arai, National Institute of AIST, Japan T. Kobata, National Institute of AIST, Japan |
| Correspondent: | Click to Email |
A porous plug made of sintered stainless steel, which is named as standard conductance element (SCE), has been developed as an open-type standard leak element for in-situ calibration of ionization gauges (IGs) and partial pressure analyzers [1]. Since the pore size of sintered filter is less than 1 micro meter, the molecular flow condition is realized up to 10 kPa of the upstream pressure of SCE. Therefore, four useful characteristics shown in below are available. (1) Flow rate is proportional to the upstream pressure of SCE. (2) Introducing various gas species with known flow rate is available by applying this single leak element. (3) Calibration using mixture gases is available. (4) Dependence of flow rate on the temperature is small and easy to compensate. In addition, the molecular conductance CS of SCE has good long-term stability of less than 3 %/year typically. No significant influence is observed by introducing water vapor and bake-out. Since SCE with CS from 1x10-10 m3/s to 2x10-9 m3/s is available, the flow rate of less than around 10-5 Pa m3/s is generated with various gas species.
Three typical applications of SCE are introduced. First is the quantization of the gas desorption rate for thermal desorption spectroscopy (TDS) [2]. The gas desorption rate was measured by a quadrupole mass spectrometer (QMS) which was calibrated by SCE with H2, H2O, N2, CO, and CO2 gases. Second is the measurement of the effective pumping speed Seff of cryopump in the range from 10-9 Pa to 10-6 Pa [3]. H2, CH4, N2, and Ar gases with known flow rate Q were introduced into the test chamber with the cryopump through SCE, and measured the pressure increment p by extreme high vacuum gauges. Pressure indications of the gauges were compensated by relative sensitivity factors for N2. The last one is the in-situ calibration of IG and QMS. The standard pressure p was obtained from Q divided by Seff, where Q and Seff were determined by using SCE and conductance modulation method, respectively. The sensitivity of IG and QMS were measured for H2, He, CH4, H2O, Ne, CO, N2, C2H4, C2H6, O2, Ar, C3H6, CO2, N2O, and C3H8.
These results show that SCE seems to satisfy almost all of requirements for the quantitative measurements in high and ultrahigh vacuum. SCE will be used as a new vacuum standard device.
[1] H. Yoshida, et.al., Vacuum 86 (2012) 838-842.
[2] S. Inayoshi, et.al, 52th Annual Symposium of the Vacuum Society of Japan (AVSSJ-52), Tokyo, Japan, 2011.
[3] M. Yamamoto, et.al., Proceedings of international particle accelerator conference (IPAC2011), San Sebastian, Spain, 2011, 979-981.