System identification of a hot cathode electron source: Time domain approach

Abstract

Electron sources with a hot cathode operating in consumption or generation modes are widely used in many vacuum devices as gas ion sources, thermionic energy converters. The main aim of this work is to get information how dynamic properties of the electron source changes within full range of work, therefore the identification of a hot cathode electron source using the step signal and the time domain approach to know dynamic parameters (DC incremental transconductance, time constant, delay time) of the electron source in full range of its operation is made. In the first part, an open-loop system identification using step response method was conducted. For the electron source with a thoriated tungsten cathode (d=0.1 mm, l=45 mm) operating in the range 1 μA to 1 mA, the time constant T varies from 0.71 s to 0.35 s, the delay time T0 from 0.04 s to 0.01 s and the DC incremental transconductance g0 from 0 to 0.0056 S, respectively. In the next step, an approximation of obtained characteristics is made and ultimate gains of thermionic emission current automatic control system for each fixed operating point are estimated. The results of similar investigations for electron sources with an yttrium oxide coated iridium cathode and a tungsten cathode have also been shown. Presented system identification approach can be successfully applied to other types of the hot cathode electron sources.