基于脉冲功率合成技术的宽微带分幅成像驱动技术研究

Research on Driving Technology of Wide Microstrip Amplitude Division Imaging Based on Pulse Power Synthesis Technology

针对行波选通分幅相机超宽画幅驱动需求,基于宽带多节威尔金森脉冲功率合成方法,设计了一款高压驱动脉冲源。基于有限元分析方法,采用仿真软件对脉冲功率合成电路进行了仿真,系统分析了端口驻波比、插入损耗、端口隔离度、幅相一致性等参数。根据仿真分析完成了脉冲功率合成电路研制,验证系统最终能够利用8路峰值电压为1.3 kV左右、脉冲宽度为3.5 ns左右、脉冲前沿在600 ps左右的单路脉冲合成峰值电压超过3.2 kV的高压脉冲,脉冲宽度在3 ns以内,脉冲前沿在600 ps以内。脉冲频谱范围在300 MHz到3 GHz范围内的两路合成效率为83.5%,特定频率下为88%,八路脉冲合成效率为58%,特定频率下可以达到68%。通过该电路合成的高压脉冲可用于驱动宽20 mm、长95 mm、等效阻抗6Ω左右的微通道板实现选通成像,验证了基于宽带多节威尔金森电路实现脉冲功率合成,提高分幅相机驱动脉冲功率的可行性。目前基于该技术的高压驱动脉冲源已应用于I-MCP1.0型分幅相机。

When a pulse current with a rise time of about 100 ns and an amplitude of tens of MA is applied to a wire array or jet load,the load will rapidly ionize and form a plasma.Due to the Lorentzian force,these plasms will rapidly implode towards the axis and eventually stagnate in the center,forming a high temperature and high density plasma and further emitting strong X-rays,a process known as Z-pinch.Zpinch has been widely used in High Energy Density(HED)physics research for decades,including radiation source development,radiation actuation science,dynamic material properties,Magneto-inertial Fusion(MIF)and Inertial Confinement Fusion(ICF).In order to explore the structure,properties and motion laws of matter in the ultra-small space and ultra-fast time scale,the research and measurement techniques of ultra-fast phenomena represented by the variometer framing camera technology have become the main tools in use.X-ray framing cameras are widely used for two-dimensional plasma imaging in the Z-pinch process.This type of frame camera requires selective pulses to excite the Microchannel Plate(MCP).Because the width of the pulse is very narrow,only a microstrip region has voltage at a time,and photoelectrons generated by the X-ray image formed through a pinhole in the region at the input surface of the MCP will be gained and be imaged to the screen on the screen.The exposure time of each image is determined by the half-width of the selected pulse and the characteristics of the framing tube.The MCP with different equivalent impedances will realize the framing camera imaging with different frames.The width and length of the transmission microstrip line of the ultra-wide frame traveling-wave selective framing camera are up to 20 mm and 95 mm,and the equivalent impedance is about 6Ω.To actuate the beamsplitter,gating pulses with electric field peaks of more than 3 kV,pulse durations on the order of nanoseconds or hundreds of picoseconds,and spectral widths of tens to thousands of megahertz is required.In this paper,the power coupling method based on Wilkinson structure power splitter is adopted to synthesize the narrow-band pulse with low amplitude into the high-voltage pulse with the required amplitude.However,limited by the characteristics of the transistor device itself,the pulse source whose amplitude is higher than 5 kV and the front edge is better than 100 ps and the jitter is better than 20 ps is close to the technical limit of electronics.To obtain higher power gate pulse it is necessary to adopt multichannel pulse power synthesis technology.In this paper,a power coupling method based on Wilkinson structure power splitter is adopted to synthesize the narrow-band pulse with low amplitude into the high-voltage pulse with the required amplitude.The large bandwidth of the multi-section impedance converter is used to improve the working bandwidth of the power coupling,so as to meet the pulse coupling of different spectrum.The simulation software is used to design the power coupling circuit with the working frequency band of 300 MHz~3 GHz,and the loss generated in the system is optimized to achieve high efficiency coupling.Combined with the high-voltage narrow pulse output and synchronization control circuit of the preceding stage,the high-voltage pulse with peak voltage exceeding 3.2 kV is synthesized by using eight single-channel pulses with peak voltage of about 1.3 kV and pulse width of about 3.5 ns,pulse leading edge of about 600 ps.The pulse width was within 3 ns and the pulse leading edge was within 600 ps.In the pulse spectrum range of 300 MHz to 3 GHz,the two-channel synthesis efficiency is 83.5%,88%at a specific frequency,and the eight-channel synthesis efficiency is 58%,up to 68%at a specific frequency.Finally,the coupled high-voltage pulse is input into the 20 mm microstrip amplitude-divider.The transmission line of the microchannel plate inside is 20 mm wide and 95 mm long,and the equivalent impedance is 6Ω.The output pulse amplitude is 1.433 kV,the pulse width is 3.63 ns,and the pulse front is 747.3 ps,which fully conforms to the design requirement that the output voltage of the tube must exceed 800 V.At present,the coupling technique can generate driving pulses for use.In the future,the coupled pulses can be shaped by adjusting the delay of the eight pulses.At present,the high voltage driven pulse source based on this technology has been applied to I-MCP1.0 framing camera and can be used to explore the high energy density physics research with Z-pinch as the core.