The design and operation of a new extractor gauge

Abstract

A new type of extractor gauge with a cylindrical reflector and a squirrel-cage grid shaped as a frustum of a cone is presented. The trajectories of electrons and ions are evaluated by numerical method, while the extraction and collection efficiency of the new gauge, as well as its x-ray current, have been studied experimentally. These results show that the new geometry with appropriate applied voltage of the gauge are favorable for enhancing the sensitivity and reducing the x-ray current. It has been found that self-modulation and ‘‘deep modulation’’ can be used to determine the x-ray current of an extractor gauge without an additional modulator electrode. An interesting result of deep modulation is that the value of modulation factor k (defined as the ratio of the collector current at modulation to normal operating conditions at high vacuum, 10−6–10−8 Torr) of 10−4 has been achieved, so that the x-ray current can be measured at a pressure 2–3 orders of magnitude higher than the x-ray limit by deep modulation. As a result of this improvement in design and operation of the extractor gauge, both of the x-ray limits estimated by comparing with a normal Bayard–Alpert gauge in geometry factor and measured by using the deep modulation are less than 1×10−13 Torr (equivalent for N2), and the sensitivity is about 25 Torr−1.