Research On Repetitive Compact PFN-Marx Type Pulsed Driving Sources

According to the requirements of mobile platform for pulsed driving sources,pulsed power technology has been promoted to the directions of repetitive-rate operation,compactness,miniaturization,lightweight and modularization.Pulse forming network（PFN）-Marx generator,due to its compact characteristics of combining energy storage,voltage step-up and pulse forming,has great potential in compactness realization and has been drawn wide attention.Based on the repetitive-rate and compact PFN-Marx pulsed driving source,the gas switches,load waveform optimization,high voltage branch switch,and other key technical problems are investigated in this dissertation.The investigation of the PFN-Marx system lays a good foundation for the development of a compact rep-rate pulsed driving source.The main points of this dissertation are as followings.1.Research on gas switches of PFN-Marx generatorBased on the structure parameters,electrical parameters,and switch working pressure of the compact PFN-Marx generator,a trigatron with spherical main electrodes has been designed.The influence of several factors on the gap field enhancement of the trigatron has been studied numerically.Under the experimental condition of working gas of N₂:SF₆（85%:15%V/V）between 0 and-160 k Pa,the trigger delay time and the jitter of the switch are 72 ns and 4 ns,respectively,at the maximum undervoltage ratio.Futher optimization on the switch insulation structure and its electrode material leads the increase of lifetime of the trigatron to more than 10⁵ times.An integrated gas switch with 22 stages has been developed and investigated based on the trigatron.The influence of the placement of the isolating inductors on switch overvoltage has been analyzed theoretically and numerically.Results show that stable switch overvoltage can be obtained by the series and parallel mixed grounding of isolating inductors.The relationship between switch built-up time,jitter,operating voltage,and rep-rate is experimentally studied.Under the experimental condition of working voltage of 42 k V,rep-rate of 30 Hz and 50 pulses,results show that the built-up time of the integrated switch is about 150 ns with jitter of 5 ns.2.Development of a repetitive compact PFN-Marx generatorIn order to improve the output waveform quality of the PFN-Marx generator,a coupling transmission line（CTL）model consisting of coupling capacitor and node inductors between adjacent PFN modules has been established.The parameters of the CTL have been calculated theoretically.The influence of the CTL on load waveform has been analyzed in detail.Simulation results show that a high frequency oscillation has been superimposed on the load waveform due to the existence of the CTL.A RC discharging circuit of the PFN-Marx generator has been put forward and the high frequency oscillation phenomenon caused by the CTL has been effectively suppressed.Data comparison shows that the energy density of a mica capacitor is higher than that of a ceramic capacitor.Based on mica capacitors,the modular PFN module has been designed.The compact modular PFN-Marx generator is realized via the design of independent of PFN module and integrated switch module.In addition,the temperature characteristics of mica capacitor and ceramic capacitor have been compared in experiment.The results show that mica capacitor is capable of a relative wide temperature,since its capacitance is increased by 2.5%when the temperature rises by50℃.In contrast,the capacitance of ceramic capacitor is dropped by 26.6%under the same condition.A primary energy subsystem based on pulse charging method has been designed and studied with theoretical,numerical and experimental methods.The experimental results show that the temperature rise of the transformer is about 5℃after operating 50pulses.It causes the increase of the resistance of the transformer primary and secondary windings,which futher resulting in the drop of the output voltage with the increase of pulse number.3.Investigation on a 5 GW PFN-Marx pulsed driving source.A repetitive compact PFN-Marx pulsed driving source with volume of 80 L and weight of 56 kg has been developed.The results show that output pulse with peak power of 5.3 GW,rise edge of 30 ns,and pulse width of 100 ns has been delivered to a50Ωresistor in single pulse operation mode.The ratio of the storage energy to volume of the generator is about 6.6 J/L.The output peak power of the generator is about 4 GW at rep-rate of 30 Hz.In addition,the output characteristics of driving a transit time oscillator at 30 Hz rep-rate mode are studied in experiment and 10 pulses of high power microwave with peak power of 400 MW and pulse width of 20 ns are generated.The pneumatic control mode has been adopted to solve the branch switch synchronization and insulation problems.A high voltage branch switch is developed and investigated.The function of discharging to two loads at different times is realized in experiment.Under the experimental condition of output voltage of 470 k V and output current of 9 k A,the time-sharing switching function of the branch switch has been realized.The pulse transmission characteristics of the branch switch are studied theoretically,simulatively and experimentally.These efforts provide a new technical method for the compactness enhancement of systems which is needed when driving multiple loads at different time with one pulsed driving source under limited volume and weight constraints.4.Study on a lightweight and compact pulsed driving sourceA lightweight and compact pulsed driving source based on PFN-Marx generator has been developed.The total weight of the system is 15 kg,of which the generator volume of 8 L and the weight of 6 kg.A novel PFN-Marx topology has been proposed by adjusting node capacitor parameters and node number in one stage of Rayleigh type PFN-Marx generator.The simulation results show that the output waveform quality of the new topology is better than that of the traditional circuit.The experimental results show that the pulse width of the output pulse is reduced due to the coupling between the adjacent PFN modules.An output pulse with peak power of 546 MW,rise edge of 25 ns,and pulse width of 100 ns is delivered to a 38.7Ωresistor load.The ratio of the storage energy to volume of this generator is about 6.8 J/L.In addition,the output characteristics of driving a magnetron at 10 Hz rep-rate mode are studied in experiment and 10 microwave pulses with peak power of 70 MW and pulse width of 75 ns are generated.