Equivalent Modeling of Microchannel Plate Framing Camera Gain Uniformity

Abstract: In X-ray framing cameras, the gating pulse will be attenuated as it transmits along the microchannel plate (MCP) microstrip cathode, which affects the dynamic gain uniformity of the MCP. A full-wave electromagnetic attenuation model for gating-pulse transmission on the MCP microstrip cathode was established to investigate dynamic gain uniformity. To improve computational efficiency, the porous MCP containing on the order of 10^7 microchannels was represented as an equivalent homogeneous medium with a frequency-dependent complex permittivity. The input signal was a combination of a −400 V DC bias and a −2 kV Gaussian gating pulse with a full width at half maximum (FWHM) of 200 ps. After propagation along the 40-mm-long and 8-mm-wide MCP microstrip cathode, the simulated signal decreased to −1.268 kV and the FWHM broadened to 293 ps. As a result, the normalized gain reduced to 31% along the pulse-transmission direction. An X-ray framing camera has been developed to verify the correctness of the theoretical model. The MCP dynamic gain uniformity was measured using an ultraviolet laser with a FWHM of 6.5 ns, which demonstrated that the gain dropped to 27%. An error-correction model was proposed, which reduced the normalized root mean square error (NRMSE) from 5.91% of the original simulation to 2.75%.