AVS 49th International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP8
Influence of Gas-Surface Interaction on Thermal Transpiration of a Capacitance Diaphragm Gauge

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Poster Session
Presenter: M. Hirata, National Institute of Advanced Industrial Science and Technology, Japan
Authors: S. Nishizawa, National Institute of Advanced Industrial Science and Technology, Japan
H. Akimichi, National Institute of Advanced Industrial Science and Technology, Japan
M. Hirata, National Institute of Advanced Industrial Science and Technology, Japan
Correspondent: Click to Email
For a capacitance diaphragm gauge (CDG), the temperature difference between the sensor head and the vacuum chamber gives a non-linear sensitivity, which is called thermal transpiration. This sensitivity depends on gas species and pressure. It is supposed that under the same condition of gas-surface interaction, the sensitivity should be normalized by mean free path regardless of gas species. However, the sensitivity dependence of mean free path is also different from gas species. For example, at molecular flow regime, the sensitivity of He is slightly small in comparison with Ar and N@sub 2@. It means that the gas-surface interaction should be different from each gas. In this study, by using a direct simulation Monte Carlo (DSMC) method, the influence of gas-surface interaction on thermal transpiration was analyzed. In case of random and cosign reflection models, the sensitivity has non-linearity and depends on mean free path. On the other hand, in case of a perfectly elastic reflection model, the sensitivity is constant regardless mean free path. In case of complex reflection that is composed of random and elastic reflections, as increasing the elastic reflection component, the sensitivity decreases from that of random and cosign reflection to elastic reflection. From these results, it is suggested that the elastic reflection component of He-surface interaction is larger than Ar and N@sub 2@ -surface interaction. It means that as decreasing the molecule diameter, the elastic reflection becomes important.