The gated X-ray framing camera (XFC) is an indispensable piece of two-dimensional diagnostic equipment used to measure implosion symmetry, hydrodynamic instability, and plasma uniformity. Therefore, this device plays an irreplaceable role in the research of laser inertial confinement fusion (ICF) and high energy density physics.

The open structure and outgassing materials of the MCP imager equipped in current XFCs may lead to the contamination of the MCP and the Au photocathode, resulting in further reduction of the gain of the framing camera as storage time prolongs. In addition, Au has a lower quantum efficiency as an X-ray photocathode, which has been found to reduce the camera detection quantum efficiency and increase the image noise. Is there a way to improve both?

A research team led by Assoc. Prof. Dr. YANG Yang from Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences (CAS) proposes a hermetically sealed MCP imager with a CsI photocathode. Compared with traditional MCP imagers, it solves the problems of poor stability and the low quantum efficiency brought by the open structure and the Au photocathodes. The result was published in Nuclear Inst. and Methods in Physics Research, A.

Schematic structure of the sealed MCP imager. (Image by XIOPM)

According to the result of their experiments, with two microstrip photocathodes of 100 nm Au and 100 nm CsI, respectively, the proposed imager has a measured exposure time of 65 ps when applied with a 200 ps width gate pulse. The image intensity of the CsI microstrip photocathode is 3.4 times that of the Au microstrip photocathode when illuminated by a non-monochromatic portable X-ray source with high energy photons.

Furthermore, the sealed structure effectively improves the performance stability of the MCP imager. After being stored in the laboratory air for 1000 hours, the sealed MCP imager recorded a 17% drop from the initial value in its static response intensity. As for the open-structured MCP imager, the static response intensity was reduced by more than half when the exposure time accumulated to more than 24 hours.

The proposed hermetically sealed X-ray MCP imager with a CsI microstrip photocathode makes a great improvement in both sensitivity and stability. With its enhanced detection efficiency and potential to reduce crosstalk and artifacts, the sealed MCP imager is expected to achieve quantitative measurements with higher precision.