Carbon velvet cathode implementation on the Orion relativistic magnetron

After decades of use, the magnetron still remains an important cross-field microwave source. In an effort to increase the peak output power researchers, within the high power microwave (HPM) community, began to investigate relativistic magnetrons in the 1980´s and these investigations continue to date. This paper reports on the results obtained when novel caesium iodide CsI coated cathode materials were evaluated within two different 10-vane rising sun magnetrons (D-Band and E-Band). These experiments were performed at the Orion HPM Facility in the United Kingdom (UK). The Orion system allows cathode designs to be tested at different narrow band frequencies from 1.07 GHz up to 3.0 GHz, within a 30% tuning range of each of the four magnetrons covering this frequency range, with high voltage (HV) pulses (/spl sim/100 kV up to 500 kV), along with variable HV pulse lengths (150 ns up to 500 ns) and at repetition rates up to 100 Hz. Earlier cathode research work, within the UK at the Orion Facility, showed that pulse shortening limited the microwave pulse lengths that were achievable by this HPM source. The relativistic magnetron suffered from pulse shortening, with the likely mechanism being expansion of cathode plasma in the anode-cathode gap. Researchers proposed that the plasma de-tuned the magnetron, thus causing the microwave interaction to turn off. This paper shows that a change in the cathode material to CsI coated material can enable the magnetron to operate at the maximum pulse duration of the HPM power supply (/spl sim/500 ns). Hence, CsI coated cathode material plays an important role in reducing pulse shortening affects, when operating within a relativistic magnetron.