Study On Gain Mechanism And Structural Optimization Of X-ray Framing Camera

Physics experiment and diagnostics are two very important contents in the current inertial confinement fusion research. The development of ICF diagnostic techniques is an important research direction, due to not perfect situation of the current theory, not ideal technology of the target fabrication, and the fact of limited power of the laser devices. Micro-channel plate (MCP) based high-speed proximity focusing X-ray framing cameras (XFC), whose measurement data is an important reference for analysis of ultrafast process, are a standard diagnostic tool for two-dimensional, time-resolved imaging and time-resolved x-ray spectroscopy in the fields of laser-driven inertial confinement fusion, high energy density physics and Z-pinch experiments.This paper summarizes the evolution of framing camera technology at home and abroad. Then taking the travelling-wave gated X-ray framing camera as an example, we introduce its basic structure and working principle. Because MCP is the core device of XFC, we also introduce its working principle, manufacturing process and structure parameters in detail. On these bases, the structure of current framing camera is optimized with the use of modular design. Besides, an electric controller is developed to generate four high-voltage gating picosecond pulses by using the method of pure electronics. Testing results indicates that pulse energy majorly distributes in the frequency range of 0 ~ 6GHz. In this passband, the transmission characteristics of microstrip line is simulated, and simulation results show that the Chebyshev and Klopfenstein impedance transformers could achieve not only the function of impedance matching, but also to transmit the gating picosecond pulse with sufficiently low signal reflection and energy loss.In order to verify the performance of the camera, we carry out static and dynamic experimental tests of XFC, using a variety of UV light source. The camera's exposure time parameter (152ps) is obtained. It is found that the fact of measured exposure time smaller than theoretical value is due to the broadened pulse width, by monitoring the gating pulse transferring through the micro-strip lines. The truth may contribute to the improvement of time resolution of the camera.Analytic method is employed to simulate the whole courses of electronic transportation, collision and secondary emission in a MCP single channel. With the use of commercially available software Lorentz-2D, we obtain such curves as initial energy distribution of secondary electrons, electron energy distribution just before colliding with the channel wall, and electron transit time distribution. These simulation results can serve as references when developing a new framing camera or trying to improve its performance. MCP sensitivity is measured, and it's found after the comparison with simulation results that the first collision will actually affect the gain of MCP. Qualitative analysis shows that parameters like bias voltage make significant impacts on the depth of the first collision. According to what is observed in the simulation, the empirical equation of the gain versus voltage, which is based on Eberhardt's discrete dynode model, is corrected to better fit the measurements. It is found that the principle of microwave attenuation is the reason that causes gain attenuation of XFC. Custom experiments are designed to measure the dynamic gain curve, and the gain attenuation constant is derived.