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SR and FEL sources and centers

Methods for counteracting of back-bombarding effect for thermionic RF guns


  • Mr. Konstantin TORGASIN

Primary authors



Thermionic RF guns find application as high brightness electron sources for RF linacs or as pre-injectors for synchrotron facilities. The thermionic RF guns have advantage over photo-cathode RF guns in their compact structure and simplicity of operation. However, for the applications where long electron macropulse duration (several µs) is required, such as oscillator type FELs, the thermionic RF guns have a big disadvantage due to the back-streaming electrons. Those electrons are accelerated in the negative phase of an RF period backwards to the cathode. The back-streaming electrons hit the cathode and increase its temperature during the macropulse. This causes a ramp in thermionic current and limits usable pulse width. The reduction of the impact of the back-streaming electrons would advance further development of accelerator technologies using the advantage of compact structure of thermionic RF guns. This work presents a short overview over concepts for reduction of the back-bombardment effect for thermionic RF guns and some examples of technical realization respectively.