Initial investigations into the role of the bremsstrahlung conversion target in the self magnetic pinch radiographic diode

The self magnetic pinch diode is routinely used at AWE as a radiographic source [1,2]. This diode consists of a hollow cathode and a planar target separated by of order 10mm. The pinching of the electron beam relies on ions being drawn back from the anode thus reducing the self repulsion that the beam would otherwise experience and allowing the self magnetic field of the beam electrons to bring the beam to a focus. A grounded foil is generally used directly in front of the conversion target and the separation of this foil to the conversion target may be altered. A number of shot series were undertaken on the EROS machine at AWE with differing conversion target material and foil to conversion target separation, the electrical records were then used to look at the change in bi-polar flow within the diode. The shape of the conversion target was also altered such that it formed a band and a further set of shot series were undertaken on the EROS machine at AWE as this band target allows the amount of conversion material to be varied while still allowing a radiographic spot to be measured. The conclusion of these shot series is that the conversion target is not required in order for the diode to operate and that the quantitative degree of pinch experienced by the electron beam is not dependent on the presence of the conversion target.