Test of the image converter cameras complex for research of discharges in long air gaps and lightning

Tests of image converter cameras (ICC) designed by the BIFO Company [1] were undertaken with the aim of checking a possibility of ICC application for recording from large distances low-luminous structures and structures existing during a short time period such as a hypothetic leader streamer zone and a return discharge corona. The main ICC elements are as follows: an image converter tube (ICT) with a microchannel plate (MCP) intensifying an electron image and a digital CCD camera. The ICT forms an image of the object to be recorded on its luminescent screen; depending on a mode of ICC operation this image is subjected to a frame sweep or a linear sweep. In case of two MCP a gain coefficient (a ratio of radiation energy at the ICT output to that at its input) can achieve 10 W/W. By means of voltage variation at the MCP, ICTs allow to adjust gain in both static mode and dynamic mode (in a process of sweep). The СCD camera readouts the image from the ICT screen and enters it into a personal computer (PC) for visualization and digital processing. A photosensor (PS) with two identical channels based on PMT controls ICC operation. The first channel comes into action at the very beginning of a discharge and triggers an ICC sweep and the second channel triggers, in the course of recording, a circuit of fast and adjustable by value gain coefficient reset when discharge brightness is so increased that the image at the ICT output may be saturated and may loose brightness gradations. An optical system of each PS channel can be focused to a required height above the earth. It is equipped with a set of horizontal slits of a various width and an adjustable length as well as with a set of different filters. All this in combination with electronic adjustment of a level of coming a channel into action allows to perform spatial, amplitude and spectral selection of input signals.