A novel solution to the gated x-ray detector gain droop problem.

Microchannel plate (MCP), microstrip transmission line based, gated x-ray detectors used at the premier ICF laser facilities have a drop in gain as a function of mircostrip length that can be greater than 50% over 40 mm. These losses are due to ohmic losses in a microstrip coating that is less than the optimum electrical skin depth. The electrical skin depth for a copper transmission line at 3 GHz is 1.2 μm while the standard microstrip coating thickness is roughly half a single skin depth. Simply increasing the copper coating thickness would begin filling the MCP pores and limit the number of secondary electrons created in the MCP. The current coating thickness represents a compromise between gain and ohmic loss. We suggest a novel solution to the loss problem by overcoating the copper transmission line with five electrical skin depths (∼6 μm) of Beryllium. Beryllium is reasonably transparent to x-rays above 800 eV and would improve the carrier current on the transmission line. The net result should be an optically flat photocathode response with almost no measurable loss in voltage along the transmission line.