Improvement of the gating efficiency of gated image intensifier tubes

Abstract

Gated image intensifier tubes (IITs) with microchannel-plate (MCP) may be used for the diagnostics of very fast transient phenomena such as predischarge development in gases. The gating pulse is usually applied to the cathode of the IIT while the voltages across the MCP and the anode remain constant. Due to the transparency of the cathode, which is in the range of 10<SUP>-5</SUP>, and the low emission energy of the MCP-material, which can be below 2 eV, a small portion of radiation is able to pass the cathode during its non-gated state and release electrons directly from the MCP-material. These electrons are amplified by the MCP which may result in an aliased picture. Therefore the amount of radiation which can be applied to the IIT during its non-gated state is limited. In order to increase the gating efficiency of the IIT combined gating of the cathode and the MCP is used. This allows us to take pictures from predischarge phenomena with very low luminosity followed by the intensive radiation of the high current arc. Similar problems exist during investigations of the recovery phase of high current switches. In addition gating of the MCP reduces all kinds of noise caused by the MCP during the relatively long integration time of the video-camera usually connected to the IIT. A single frame high speed camera with gated photocathode, gated MCP, and variable exposure times between 700 ps and 5 ns has been developed. The transparency could be decreased from 1E - 5 of less than 1E - 13.