Investigation of an X band experimental magnetron through MAGIC modelling

Summary form only given. We have investigated the operation of an X band experimental magnetron by using 3D MAGIC code. This magnetron has 18 cavities and a strapped anode, but exhibits a typical efficiency of approximately 40%. In the previous magnetron model, we have obtained a total efficiency of around 50%. We have devoted considerable efforts to identify the possible causes for a lower efficiency in the real magnetron. Firstly, the leakage current due to the emission of the inner side of the end-hats has been included in the model. This has resulted in a drop of the efficiency of the tube to the region of the measured values at individual points. However, it has not been possible to replicate the characteristic curves for the magnetron. So the leakage current seems not to account for the low efficiency on its own. Secondly, we have studied different emission models of the cathode. The previous Space Charge Limited Model is replaced with the Beam-Emission model, which can vary the cathode emission current density, in an attempt to more accurately model the emission characteristics of the cathode surface as this is not a simple emitting surface in the magnetron under study. It is shown that the efficiency decreases as the cathode emission current density is decrease. Finally, when we replace the uniform axial magnetic field employed in the previous model with non-uniform one which was applied to the real tube, very different simulation results have been obtained. Therefore, the uniform axial magnetic field is not accurate enough for magnetron modeling. In summary, possible causes for low efficiency in an X band experimental magnetron have been investigated in the MAGIC model. These simulated results verified in the experiment in due course.