Investigation Of Solid Pulse Forming Lines With Slow-Wave Structure

Pulsed power technology is suited to drive electrical loads requiring very large power pulses in short bursts?high-peak power?.It has important applications in many fields such as industry,environmental protection,medical treatment and bioelectronics.Pulse forming line?PFL?is one of the basic components of a pulsed power system,which is widely used in intermediate stages to generate the high power pulse with hunrads nanoseconds pulse duration.In many applications,there is an overwhelming need to provide the compact,portable and long-pulse-duration pulsed power systems deployed in small spaces under stressful environments,while the traditional liquid dielectric is difficult to meet them in PFL as the storage medium.Ceramic attracts strong interest in pulsed power technology due to its essential characteristics such as stable environmental adaptability,high energy storage density since it can behave in a high dielectric constant and high breakdown strength at the same time.Unfortunately,the difficulty of manufacturing large ceramic bulks also influences its extensive use in pulsed power systems,so the thin thickness is usually adopted to the solid PFL modules and then the thin PFL modules are stacked to generate the high power pulse with certain duration time.Through combining with the hot application requirements and promising prospects such as compactness,modulazation,long pulse duration and solid-state,several typical designs for the solid state pulse forming modules are presented and investigated in this dissertation,and the relevant key technologies and physics are also revealed.The main contents and innovative points are as follows.1.Investigation of the solid helical PFL?HPFL?A new type HPFL with outer helical surface structure is studied.The electromagnetic dispersion theory is used to calculate the important parameters of the HPFL based on tape helix model.Dispersion effects on the important electromagnetic parameters of HPFL,such as electric length?half of the pulse duration?and characteristic impedances,are analyzed.When Al₂O₃ ceramic is applied to be the dielectric in the HPFL,the pulse width of the HPFL is calculated nearly 50 ns only with the length of 305 mm.Electromagnetic field simulation can draw the dispersion curve of the HPFL directly,which can describe the dispersion effect on the electric length of HPFL.Furthermore,the electromagnetic field simulation and experiments are carried out to verify the theoretical calculations of the pulse wide and characteristic impedances.Both simulation and experimental results can prove the electromagnetic analyses and calculations in this paper.At present,the Al₂O₃ HPFL can hold off voltages larger than40 kV at microseconds-charging-time range.At last,one stage Blumlein line with different angle between two HPFLs is tested to measure electromagnetic coupling effects and the amplitude of ouput pulse is nearly equal to the charging voltage with different angle,which means that the coupling effect is weak in the two designed HPFLs as the Blumlein line.2.Investigation of the solid Meander PFL?MPFL?Nowadays,most of the solid-state circuits are of the strip type and its fabrication is very convenient by utilizing the 2-D manufacturing technology.In printed circuit boards?PCBs?,the circuit designers usually adopt the common meander lines to be the delay lines,to produce delay between two points?or devices?while occupying as little board space as possible.Using quasi-TEM approximation and parralle conductor line methods,dispersion effects on the important electromagnetic parameters of MPFL,such as electric length?half of the pulse duration?and characteristic impedances,are analyzed under the conditions of different electrode thickness or environmental dielectrics.In particularly,we use a glass-ceramic substrate,with the dimension 250 mm×95 mm×4mm,to deliver a high voltage pulse on the 7.5?load with pulse duration longer than120 ns.Experimental results show that the glass ceramic substrate can hold off voltage higher than 20 kV,and the high breakdown strength is not achieved up to the 26 kV/mm level which the same thick bulks without electrodes.Moreover,the distributions of the breakdown points have regularities,which present the edge effects on the field enhancement at specialized areas.Simulation results also indicate the same phenomena,and a simplified model is built to find ways to decrease the edge effect on the field enhancement.3.Investigation of the new solid Dual MPFL?DMPFL?A new type solid DMPFL is proposed.The new strustural designs are investigated to the improved withstand voltage performance of thin electrode in MPFL.In details,by forming two MPFL electrodes on the same substrate with the same start area and the end area of the line,the?break‘area has been removed.The connected two MPFL on the same substrate both charge and discharge in parallel,not the same as the working theory of Blumlein-line or Marx-line which two lines discharge in series.Using the same glass ceramic substrate,the impedance and the pulse duration are calculated as 3.7 ohms and 85 ns by the previous calculation methods,respectively.Experimental results show that the DMPFL can hold off voltage higher than that of MPFL.4.Investigation of the other pulse-forming modules structure to increase the pulse durationSeveral new type pulse-forming modules are described,including LC pulse-forming module and concentric ring planar PFL.In particulariy,inspired by the rapidle development of the multilayer ceramic capacitor?MLCC?in mordern power electronic,a coxial pulse forming module based on the manusfacturing process of the MLCC is presented.The square pulse forming ablitities of new type pulse-forming modules above have been investigated by simulations and experiments.5.Investigation of photoconductive semiconductor swiches?PCSS?with solid PFL employed in the solid state pulsed power systemA solid-state pulse generator module combining solid state slow-wave pulse forming lines with photoconductive semiconductor switch is presented.To achieve the synchronization of the multiple pulses,the GaAs PCSS triggered by compact laser diode are used in the one stage Blumlein line composed of two HPFLs.After 30 times consecutive group tests,the jitter of delay time between command signal?3V?and output pulse is 612 ps.A high power pulse with 50 ns pulse duration,18.5 kV can be obtained by the module.However,when the nonlinear mode GaAs PCSS is employed in the one stage Blumlein line composed of two glass-ceramic DMPFL with low impedance,the large current do harm to the GaAs PCSS for the characteristic of filements current.Next,the trigger generator based on GaAs PCSS by laser diode triggering is prensented,aiming to take the advantages of the low-jitter compact characteristics and avoid the large current that is harmful for the nonlinear mode PCSS.In trigger circuit,a 200 pF capacitor is charged by microseconds pulse with amplitude of 18 kV and then discharges by the high gain mode GaAs PCSS to trigger the high power trigatron switch.Triggered by the fast rise time¹0 ns pulse generated by PCSS,the DC charged trigatron can be operated on the voltage up to 24 kV with rise time 10ns and 40 consecutive tests show 1.5 ns delay-time jitter.PCSSs show a bright future in ns or sub-ns multi synchronization applications.