FIRST RESULTS OF THE 25 PIXEL HPD

Speed properties, signal shape, response uniformity and magnetic field behavior of a 25 pixel, proximity focused HPD have been measured in d ifferent experimental conditions. Using 30 ps wide laser pulses, rise times of less than 1 ns and 10 ns long trapezoidal pulse shapes (at 20 0 V bias) have been observed. The 25 pixel HPD was measured to have go od integrated charge response uniformity without charge losses or gain variations across pixel boundaries, although a spatial scan showed so me significant pulse height and pulse shape variations near the border s between pixels. These pulse shape variations were traced to disconti nuities of the electric field inside the chip. The signal shape unifor mity is expected to be restored by reducing the pixel to pixel gaps. W ell separated single photoelectron peaks have been registered. Magneti c field tests yielded results compatible with what already published. (C) 1998 Published by Elsevier Science B.V. All rights reserved.