Development of intense electron beam diodes for use in deep penetration radiography at AWE Aldermaston

The Atomic Weapons Establishment (AWE) UK has a number of pulsed power driven flash X-ray machines that are used to take transmission radiographs of hydrodynamic experiments using Bremsstrahlung radiation with end-point energies up to 10 MV. A project is taking place to develop a new facility with higher voltage (14 MV) flash X-ray machines using inductive voltage adder (IVA) drivers. Diodes that can deliver high dose (1000 Rad @ 1m) in a small source diameter (2mm) are required for these drivers. Both high impedance (several hundred Ohm) and low impedance (<50 Ohm) diodes are being researched as possible radiographic sources. This paper discusses the advances made in characterising and overcoming the physical interactions limiting the performance of the various candidate diodes. Factors that limit performance include electron ion interactions, magnetic hose instabilities and plasma creation within the anode cathode gap. Some of the methods used to overcome these problems involve creating plasma filled or cryogenic cells within the diode. Collaborations with other groups and establishments involved with electron beam diodes and radiography are also discussed.