Photomultiplier Control by a Clamping Cross-Bar Grid

This paper reports on the possibilities for locating light events randomly distributed in a plane by using only one photomultiplier with original electron optics. This experimental 2 inch phototube designed at LEP allows a spatial and temporal control of the electron emission from small elements of the photocathode. The originality of the tube lies in the use of a cross bar control grid embedded in the glass of the window at a short distance (d = 1 mm) from the photosensitive layer. The amplitude of the anode signal obtained in response to a light flash is dependent on the electrical voltage applied to the X or Y wire of the grid associated with the excited element of the photocathode. In such a way it has been shown that the position of a point light source scanning the photocathode plane of the PM could be determined with a resolution of 5 mm. Some results obtained by using a coding process to supply the blocking electrical pulses are given.