New developments in pulsed power technology and associated electron beam transport mechanisms at the United Kingdom Atomic Weapons Establishment

The Pulsed Power Group at AWE is interested in the generation of small, intense, multi-megavolt X-ray sources for radiographic applications. For this paper, research has been carried out into electron beam transport and focusing studies on one of our single pulse forming line flash X-ray machines. Experiments were undertaken on E Minor to improve the radiographic spot size generated by our 'paraxial diode'. This is a novel anode/cathode assembly designed to produce a small diameter electron beam focused onto a high Z target. Electrons are propagated through a gas-filled cone such that their electrostatic repulsive and magnetic attractive forces are almost cancelled. The cone's length and gas pressure were initially optimized and then specific gas species applied to the drift cone. Helium gas improved spot size stability whilst the addition of a 'secondary cell' to increase the neutralization of the electron beam's self-electric forces yielded a 30% improvement in measured spot size.