Investigation Of A Compact Low Impedance Marx Generator With Quasi Rectangular Pulse Output

In recent years,pulsed power has evolved to play an important role in scientific research as well as industrial and commercial fields.One of the reasons is that the pulsed power system is becoming more and more compact,portable,and reliable.Compact pulsed power system is widely applied in radiographic and high power microwave.Apart from being compact,the system has to meet a few other requirements.First,the lower the impedance of the source the higher the voltage delivered to the diode load.Second,pulse shape and flatness of the peak voltage are also important factors,as shorter pulse leading edge and a proper flat-top can help maximize radiation dose or microwave power within the allowed pulse duration or diode impedance lifetime.To sum up,the desirable pulse power source should be compact,low impedance,short rise time,and flatness of the peak voltage.The Marx generator is basically an array of high-voltage capacitors initially charged in parallel and simultaneously series connected,causing a multiplied high-voltage pulse across the load.Compact,low impedance Marx generator can directly drive diodes to produce x-rays or high power microwave.However,as load requires the driving voltage to have a flat top,PFN-Marx with pulse forming networks or pulse forming line rather than capacitors has achieved rapid development.In this paper,A low impedance compact Marx generator with near-square pulse output based on the Fourier theory is developed.In the Marx generator the drive currents of different discharge frequency generated at different capacitance are superimposed to form quasi-rectangular output pulse voltage.It is an effective way to generate a high-voltage quasi-rectangular pulse with width of 100 ns at low impedance load.It also has high energy density and power density and therefore is very compact.Some results as following:(1)Discharge characteristic of an ideal module with infinite branches is calculated theoretically.The result shows that the module has the same characters as a pulse forming line.And the module has infinite driving circuits in parallel and each driving circuit has the same inductance,and capacitance is in inverse proportion to the square of odd number.And then finite capacitors was considered.The value of different capacitors and inductors has been calculated from the conservation of energy.A methord how to design the module has been discussed from the simulation results.The influence of the series resistant of capacitors and magnetic field coupling between different discharge branches has also been discussed.(2)A three-branch and a two-branch module are designed and tested.The former can output a electric pulse with current of 15.7kA,risetime of 27.8ns,pulsewidth of 156ns and flattop(95%-95%)of 110ns at a load of 1.6 Ω.The two-branch module has an impedance of 1.2 Ω.When charging voltage is 100.6 kV and load resistance isl Ω,the peak output pulse is 45.2 kV voltage,the peakpower is about 2 GW,the pulse width is about 130 ns,and the rise time is about 35 ns.The energy density and power density of the module are 15 kJ/m3 and 140 GW/m3,respectively.A four stage Marx was build based the two-branch module and the test shows a good output results.(3)A 16 stages Marx generator with near-square pulse output has been designed.First the inductances of different branches were calculated from a staic magnetic simulation.Magnetic oupling between different branches and different modules also has been discussed from the simulation.Design and analysis of gas switch,charging and grounded inductor has been accomplished and all parameters has been obtained from simulation or testing results.A full circuit of the Marx generator has been built from parameters of modules and a resistant model of the gas switch from literature.And then influence of the charging and grounded inductor was analyzed.Output wave at different charge voltages also been calculated from the circuit.(4)Erection process of the Marx generator has been analyzed.Influence from the grounded capacitor of the switch electrode and the isolated inductor(including charging inductor and grounded inductor)has been discussed by academic calculation and simulation from a 3 stages Marx.And the coefficient of the over voltage from different circuit including traditional method,coupling capacitor method and grouped isolated inductor method.The waveform of the third switch in the 16 stages Marx generator has been simulated from different methods.And the impression was compared.(5)A marx generator consists of 16 basic quasi-rectangular modules has been investigated.The Marx generator was designed to provide a fast rise time of about 30ns,the full-width at half-maximum(FWHM)of 120ns.Test results show that the generator can deliver voltage of 550kV and power of 20GW to the load.The voltage pulse is rectangular in profile as expected,with a risetime(10-90%)of 32 ns and a pulse duration of 120 ns.The simulated output voltage and the experimental recording one accurately fit each other except the rise step of the pulse.A new model including process of each self-breakdown switch has been built for improving simulation.Final the errection of the Marx at different earth capacitor has been tested and discussed.