The Research Of Long-lifetime Cathodes For Applications In Magnetically Insulated Transmission Line Oscillators

Magnetically insulated transmission-line oscillator(MILO)is a popular high power microwave device because of its advantages of compact volume and light weight.Currently the usual velvet cathode applied in MILO has the advantages of low emission threshold electric filed strength,good emission uniformity and high current density,however,its drawback of short lifetime limits the long-lifetime and stable operations of MILO.On this background,a long lifetime cathode is on research to enable the MILO has a long maintain-free lifetime and performs as well as when a velvet cathode is mounted.The main works and conclusions are listed as follows.1.Two kinds of cathode structures for MILO applications were designed and manufactured.The fibers array structure and circle plates array structure were designed for radial electron emission,and a carbon fiber array cathode and a glass fiber cathode were manufactured based on the two structures.2.Emission characteristics of three cathodes were studied comparatively.Three cathodes was tested under conditions of diode voltage of 100 kV,pulse duration of 30 ns and current density of about 70-100 A/cm~2,while the voltage was changed in the test of the emission threshold electric strength.According to experiments results,the carbon fiber array cathode has a emission threshold electric strength smaller than 21.7 kV/cm,the velvet cathode has a emission threshold electric strength smaller than 38.3 kV/cm and higher than 31.7 kV/cm,and the glass fiber cathode has a emission threshold electric strength smaller than 30 kV/cm.The outgassing rate of the carbon fiber array cathode,velvet cathode and glass fiber cathode are 6.93 atoms/electron,85.8atoms/electron,14.24 atoms/electron,respectively.The carbon fiber array cathode has the best stability on 20 Hz operations,while the velvet cathode performs worst.The lifetime of the carbon fiber array cathode and glass fiber cathode are longer than 10000pulses and 1500 pulses,respectively,while the velvet cathode has a lifetime of about2000 pulses,so the lifetime of the carbon fiber cathode is much longer than that of the velvet cathode.3.The three cathodes were applied for MILO operations comparatively.The three cathodes were applied in a high-efficiency MILO which can generate microwave in L-band with peak power of several GW.The experiments results present some important conclusions.The output microwaves of the MILO generally have the same pulse durations for the three different cathodes.The power efficiency of the carbon fiber array cathode is almost the same as that of the velvet cathode,while the power efficiency of the glass fiber cathode is a little lower than that of the velvet cathode.Generally the power efficiency of the carbon fiber array cathode on single shot mode and repetitive mode are 16.1±1%and 13.5±1%,respectively,while it is about14.8±1%and 12.6±1%for the velvet cathode,and the power efficiency of the glass fiber cathode on single shot mode is about 13.9±1%.Under the condition of output microwave power of several GW,the lifetime of the velvet cathode is smaller than 300pulses and it is longer than 800 pulses for the carbon fiber array cathode.In conclusion,the carbon fiber array cathode applied in MILO has advantages of high power efficiency,long lifetime and low outgassing,and this is very meaningful for the research of a high-efficiency,long-lifetime and high-repetition rate MILO.