Experimental investigation of thermionic cathode properties of ultrafine tungsten filament

Abstract

The thermionic cathode emission properties of an ultrafine tungsten filament are investigated with the accurate filament temperature (T) measured by an infrared pyrometer. The results show that the tungsten filament begins to emit electrons at T of about 1800 K, and the maximum electron emission efficiency (∼20 mA/W) occurs at T of about 2900 K. Moreover, the effective filament area for electron emission reaches saturation after T exceeds 2700 K. For a tungsten hot-cathode, a using standard is recommended that its operating temperature should not exceed 2600 K, the electron emission current density should not exceed 0.5 A/cm2, and the electron emission efficiency should be less than 5 mA/W. Additionally, the relation between the thermal emissivity of tungsten filament and T is also studied, showing a nearly linear increase of the thermal emissivity from 0.23 to 0.31 with T increasing from 1700 K to 2500 K and a saturated thermal emissivity of 0.48 at T of about 2900 K.