| 摘要 |
An electron impact ion source comprises an electron repeller 1144, a thermionic cathode 1138, an electron lens 1154, an electron extractor 1140 and an ionisation chamber 1108. Voltages are applied to the electron repeller, the thermionic cathode, the electron lens and the electron repeller so as to emit electrons from the thermionic cathode, accelerate the electrons towards the ionisation chamber, and generate a potential valley or potential well at the electron lens for decelerating the electrons. The decelerated electrons form a virtual cathode 1162 which is characterised as a high density accumulation of electrons. The electrons from the virtual cathode may be accelerated into the ionisation chamber to produces a low energy yet high intensity electron beam for soft electron ionization. The electrons may be decelerated to near zero velocity in the potential valley. |
