AVS 45th International Symposium
    Partial Pressure Measurements and Process Control Topical Conference Thursday Sessions
       Session PC-ThA

Paper PC-ThA5
Emission Free Measurement of Residual Gas in XHV Using Ionization by Trapped Electrons in Magnetic Field

Thursday, November 5, 1998, 3:20 pm, Room 317

Session: RGA Characteristics and Calibration
Presenter: A. Yamamoto, KEK, Japan
Authors: A. Yamamoto, KEK, Japan
S. Kato, KEK, Japan
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One problem associated with partial pressure measurement in an extremely high vacuum ( XHV ) region is outgassing from an ion source of a residual gas analyzer (RGA) itself. In order to reduce the outgassing, an improvement of its structural materials of the ion source was reported previously.@footnote 1@ However there still remains a problem of thermal outgassing from the ion source as far as a hot filament is used. Therefore, it is required for suppressing thermal outgassing to limit a time of electron emission from a filament. In this work we used a hot filament for a limited time in the beginning of the measurement. Adopting an axial magnetic field to a cylindrical anode to make a flight time of emitted electrons long, we could keep electrons trapped inside. These trapped electrons allowed us to ionize the residual gas without the thermal outgassing. But dwindling of the number of electrons due to the electron - gas collisions leads to decreasing of ion currents. We measured a dependence of the decay of ion currents for He, Ne, N2 and Xe on a gas pressure in a range of 10@super -7@ to 10@super -8@ Pa. And we also compared the decay of ion currents for the different gas species in the same pressure range. We verified that the decay time decreased with an increase of the pressures or the molecular diameters. @FootnoteText@ @footnote 1@S.Watanabe, M.Aono, S.Kato, J. Vac. Sci. Technol. A 14, 3261 (1996).