三格子変調Ｂ‐Ａゲージの静特性

Abstract

A modulated gauge, which is a special Bayard-Alpert gauge with two additional concentric grids inside the electron collector grid, was investigated. The static characteristics of this gauge for three modulation methods were measured and compared; the method of modulating the potential of the intermittent grid is considered to be the best.Much effort was made for the reduction of the modulation factors of background current (noise current). That is, the causes which induce the change of X-ray photo-current with the modulation, and the causes which induce the local pressure change by the change of electron stimulated gas desorption with the modulation, were carefully removed. Furthermore, to avoid the effects of reverse X-ray photo-emission and electron stimulated ion desorption, the intensities of the noise currents themselves resulting from these phenomena were reduced.The collector currents in the “on” and “off” states (Ion and Ioff) were measured at various pressures, and it was confirmed that the relationship between the difference-value (ΔI=Ion-Ioff) and the pressure was sufficiently linear down to 8×10-9 Pa (6×10-11 Torr). It is believed that this linearity is kept also in the lower pressure region, although this could not be confirmed because of the insufficient accuracy of the DC electrometer used in this study.