磁脉冲压缩的分幅相机超快选通脉冲研究

Research on Ultrafast Gating Pulse of Framing Camera Using Magnetic Pulse Compression

为拓展脉冲功率技术在超快诊断领域的发展和磁脉冲压缩技术的应用,基于磁性元件良好的开关性能和脉冲宽度压缩原理,采用具有多重压缩特性的级联磁开关,设计磁脉冲压缩电路,并将输出的皮秒选通脉冲应用于分幅相机时间分辨率研究。研究结果显示,磁脉冲压缩电路能产生适用于分幅相机的皮秒选通脉冲,当直流电源为500 V,磁开关电感量为1μH,初级线圈回路充电电容为4μF,变压器匝数比为10∶1,磁开关线圈匝数比为1∶2,复位电流为1 A,次级线圈回路和两级磁开关电路充电电容为1 pF时,获得幅值为-3.2 kV和半高宽为149 ps的选通脉冲,将其加载于采用蒙特卡洛法建立的微通道板通道内光电子动态倍增模型,通过计算随选通脉冲的时变增益和构建微通道板上的时间-增益曲线,可实现87 ps的分幅相机时间分辨率。研究结论可为应用于分幅相机的皮秒选通脉冲产生以及磁脉冲压缩电路的拓展应用提供新思路。

The picoseconds framing camera is an ultrafast diagnostic device,which effectively measure the spatio-temporal evolution of plasmas at the implosion stage of fusion in the inertial confinement fusion experiments.The temporal resolution of the Microchannel Plate(MCP)framing camera is 60~100 ps,that closely related to the thickness of the MCP and the parameters of picoseconds gating pulse.Although the temporal resolution is improved using the 0.2 mm MCP,the thin MCP is difficult to widely apply due to the poor signal-to-noise ratio and high fabrication requirements.Therefore,for the MCP farming camera,the higher performance of the picoseconds gating pulse is gradually became an important research work.Currently,the picoseconds gating pulse is generated by the Marx generator and the pulse shaping circuit,however,due to the complex multistage structure and the higher voltage discharge ignition,the maintenance work is tedious,therefore,it is necessary to design picoseconds gating pulse using the a method of the simple topological circuits and the high voltage device.In order to explore the new technology and expand the development of high-power pulse technology of the ultrafast diagnostics,in the course of studies of the gating pulse of the MCP framing camera,firstly,the basic characteristics of the magnetic switches and transformers are introduced,the working principle and topology structure of the circuit of magnetic element are sketched,the influence of circuit parameters on output performance is analyzed;Secondly,the multilevel magnetic pulse compression circuit is designed based on the excellent switching performance of the magnetic components and the principle of the pulse compression,which included foundation,first and second level.The influence of circuit parameters on the amplitude and the Full Width at Half Maximum(FWHM)of the gating pulse are analyzed,that included the DC power supply,the reset current,the charging capacitor and the turns ratio of magnetic switch.The optimal output of the gating pulse is discussed;Lastly,according to structure of the MCP,the dynamic multiplication model of photoelectron in the MCP channel is built using the Monte Carlo method,and the optimal output of the gating pulse is loaded on the model,the number of secondary electrons,the axial displacement and the transport time are analyzed,the corresponding gain of the photoelectron through the MCP channel is calculated,and the temporal resolution of the MCP framing camera is achieved by the curve of the time and gain on the MCP.The picoseconds gating pulse is realized by the multilevel magnetic pulse compression circuit.With increasing the DC power supply and reset current,and decreasing the charging capacitor and the turns ratio of magnetic switch,the amplitude of the gating pulse is gradually improved.With decreasing the DC power supply,reset current,the charging capacitor and the turns ratio of magnetic switch,the FWHM of gating pulse is gradually narrowed.When the DC power supply is 500 V,the reset current is 1 A,the inductance of the magnetic switch is 1μH,the charging capacitance of the primary coil circuit is 4μF,the turns ratio of the transformer is 10∶1,the turns ratio of the magnetic switch coil is 1∶2,and,the charging capacitance of the secondary coil circuit and the two-stage magnetic switch circuit is 1 pF,the amplitude and the FWHM of the gating pulse are-3.2 kV and 149 ps,respectively.As the gating pulse is loaded on the dynamic multiplication model of photoelectron,the temporal resolution is achieved to about 89 ps by calculating the corresponding gain of the photoelectron through the MCP channel and constructing the curve of the time and gain on the MCP.Based on the excellent switching performance of the magnetic components and the principle of the pulse compression,the multilevel magnetic pulse compression circuit is designed using the magnetic switches and transformers,the gating pulse with the high amplitude and the narrow FWHM is realized by optimizing and matching the circuit parameters.While the gating pulse is loaded on the dynamic multiplication model of photoelectron,the curve of the time and gain on the MCP is constructed and the temporal resolution of the MCP farming camera is calculated.The research results show that,it is feasible to utilize the magnetic pulse compression circuit generated the gating pulse,which is appropriate for the MCP framing camera.And the higher performance is realized by adjusting the direct current power supply,the reset current,the charging capacitor and the turns ratio of magnetic switch.In conclusion,this research can provide a new idea for the picoseconds gating pulse of the MCP framing camera.