Injection and Capture of Electrons in the UCI Stellatron

An l=2 stellatron accelerator is under experimental study. The stellarator field has a strength of up to 10 kG and a rotational transform angle χ ~ 0.1. Electrons are injected from either a thermionic emitter or a field-emission cathode placed inside the torus. Typically, a 20 kV, 2-4 μs pulse is applied to the hot cathode which emits ~ 3 A. A 2 MeV, 200 A beam is formed due to betatron acceleration which immediately follows the injection. The injection voltage is raised to 60 kV with the cold cathode emitting ~ 30 A for ~ 0.4 μs. A significant increase in beam current is not observed. A beam in excess of 500 A is generated by injecting plasma and electrons simultaneously at the beginning of the stellarator field and starting the betatron acceleration after the plasma has diffused throughout the torus.