Influences of Input High Voltage Waveform on the Output of Magnetron with Diffraction Output

In this article we simulate the operation of Magnetron with Diffraction Output (MDO) with different input waveforms, which include two near square waveforms with different rise time and fall time, and a Gaussian waveform. The latter is closer to the scenario that the output of the Marx Generator (MG) waveform been fed directly into MDO. The results show the rise time of the high voltage waveform has a significant influence on the output power of MDO. A longer voltage rise time waveform suffers very low output power. A Gaussian waveform, which inherently means no flat-top part, suffers the same dilemma but produces more particles than the second case. Long voltage rise time means inefficiency in building up a substantially higher than space charge limit cathode current, thus it considerably reduces the peak output power. Also, the voltage fill factor, which means the area ratio between a voltage waveform and a perfect square waveform, is considerably lower in a Gaussian waveform case. This means the total input energy to the cathode is much lower in Gaussian waveform case than a square waveform case, therefore the total microwave output energy is also lower. Conclusion is an intermediate energy storage is still necessary in pulsed power system despite substantial energy is lost in the peaking spark gap stage.