Technique Research On The PFN-Marx Generator Based On Mica Capacitors

In the field of high power microwave technology,pulse forming network(PFN)-Marx generator is one kind of the significant compact pulse power drivers which has the advantages of compact structure,low input voltage,short high voltage time,less isolation pressure and the high quality of output waveform.High voltage mica capacitors as fresh storage energy capacitors of the compact solid state PFN-Marx generator,have some perfect characteristics such as good shape plasticity,high isolation voltage,solid-state,stable performance and good temperature property.Considering all above,this dissertation presents the investigations of a PFN-Marx generator based on mica capacitor.Firstly,the mica capacitor test platform was designed and established,and the mica capacitor's characteristics of capacitor inductance and lifetime were studied in the experiments.Secondly,the property of PFN-Marx generator output waveform was studied through theoretical analysis and computer simulation,and a method of waveform adjustment of the PFN-Marx generator was put forward,which is called single stage network adjustment method.Finally,according to this method,a5-stage and 2-node PFN-Marx generator based on mica capacitors was designed,established and then studied in the experiments.The main results of this dissertation are list as follows:1.The study on the pulse discharge characteristics of the mica capacitor.Firstly,based on the assumption that the same batch and model mica capacitors have same inductance,the mica capacitor' inductance was measured by using the shortcircuit discharge method.No matter by using 2 capacitors in parallel pattern or 2capacitors in series pattern,the measured mica capacitor's inductance is around 30 nH in the experiment.Secondly,the mica capacitor lifetime test platform was designed and established,and the mini-trigger was made up with integrating Marx generator and transformer.The designs of magnet-core transformer as well as the influence of the primary coils connection are all presented in the dissertation.And the tested transformer unstable performance which was caused by magnetic core saturation was solved.In the level of 50kV's charging and 10Hz's repetitive frequency,9 mica capacitors were tested in two modes that one mode is 1500 pulses continuous operation and the other is 5100 pulses continuous operation.And the relations of capacitor's capacity,temperature,loss angle tangent value,and the lifetime were analyzed.The experimental data indicates that the tested capacitor's parameters of C,T and tg? increased with the discharging times increase and the average discharging lifetime of the tested mica capacitors is more than 60 thousand times in both modes.Besides,through the test of mica capacitor lifetime,the operation characteristics of the trigger gas switch were studied.Theexperiment data shows that the gap switch can operate stably more than 500 thousand times when change the isolation gas and trigger electrode regularly.2.The proposing of single stage network adjustment method.According to the typical PFN-Marx generator model,the single stage network adjustment method was put forward.The influence of altering capacitors parameter in one stage of PFN-Marx generator on the output current was analyzed by mathematics,and the influence of the capacity of node-capacitor in first stage on the output waveform was studied by the help of Pspice circuit code.The adaptation of the adjustment method for the multi-stage PFN-Marx generator,the influence on the output waveform of the node number in adjusted network and the influence of the adjusted network position in the PFN-Marx generator were analyzed by simulation.The analysis showed that the adjusted method can adapt to various PFN-Marx models;the adjustment process is more easily if the adjusted stage has more nodes;the position of the adjusted stage has no impact on the output waveform and the total capacity in each stage has to roughly equal.Furthermore,the detail procedures of the adjustment method were introduced.3.The simulation and experimental study on the PFN-Marx generator structure with one adjustment stage.Based on the adjustment method,an adjusted 3-stage 2-node generator and a5-stage 2-node PFN-Marx generator was designed separately.Through simulation study,the corresponding low voltage experiment circuit was established and the quasi-square pulse was obtained with a rise-time of about 30 ns and a flattop-time of about 110 ns.The low voltage experiment verified the technical feasibility of the PFN-Marx generator.Finally,the adjusted 5-stage 2-node PFN-Marx generator based on the new mica capacitors outputted quasi-square pulses of 80 kV,110ns in experiment.