The design and operation of a new extractor gauge

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.