Power flow in the output section of the 14 MV AWE-IVA accelerator

Summary form only given. The radiographic source for a new Hydrodynamic Research Facility (HRF) at AWE, Aldermaston is a 14 MV, 100-kA to 150kA, Induction Voltage Adder (IVA) designed by AWE and PSD. At the end of the accelerator the inner and outer conductor of the magnetically insulated transmission line (MITL) are flared into a larger radii dustbin region. The inner conductor (cathode) terminates in a shaped non-emitting dome attached to an emitting sphere on rod, which makes up the cathode of an intense paraxial-focussed diode. This paper reports on electromagnetic particle-in-cell (PIC) simulations of the power flow from the end of the accelerator through the diode. Since the ideal current for the focussed diode is 40-60 kA the non-emitting dome is intended to shunt the remaining current to the outer conductor without disrupting the focus. The LSP PIC code was used to calculate the voltage and current delivered to the paraxial-focussed diode for different A-K spacings, accelerator output impedances, and MITL geometries (length and shape of taper as well as different radii). We also investigated the impact on power flow of emission from a portion of the dome, which is impacted by the MITL vacuum flow electrons. The ability of the non-emitting dome to re-trap a portion of the vacuum flow electrons in the cathode prior to the focussed diode is also addressed. The voltage input to the simulation was taken from the transmission line code predictions for the voltage at the entrance to the dustbin. Using a realistic voltage waveform was important since the shape and position of the shunting vacuum flow electrons depended strongly on the rate of change of the voltage. Interpretation of the simulation results also requires that the large capacitance of the non-emitting dome be considered. Initial results imply that the output section of the AWE-IVA can be designed to function as desired.