The Microsphere Plate: A new type of electron multiplier

Microsphere Plates (MSPs), a new type of electron multiplier, consisting of sintered disks of glass beads, have recently become available from El-Mul Technologies Ltd. The principles of MSP operation are similar to those of microchannel plates (MCPs). We present a survey of the gain, resistance, dark noise, count rate capability, charge abstraction lifetime and image characteristics of a number of standard microsphere plates (of thickness 0.7 and 1.4 mm), operated both singly and as two-stage multipliers. Modal gains lay in the range 2.4-43 pC with pulse height relative FWHM values as low as 52%. MSP dark noise is relatively low (similar or equal to 0.5 counts cm(-2)s(-1)) for well-chosen lower level discriminator settings. The image response is globally uniform, having local variations in image intensity on sub-mm scale, corresponding to the structure of MSP Spatial resolution of an MSP detector may be better than 250 mu m FWHM. No dependence of the gain on the angle of radiation incidence was observed for an angular range of 90 degrees+/-25 degrees (relative to the MSP surface), while the 2540 Angstrom UV relative detection efficiency varied by 10-15% over the same range. Lifetest measurements revealed that after removal of 8 X 10(-4) C cm(-2), the detector modal gain fell from 8 pC to half of its initial value. This fall in gain was compensated by raising the bias voltage.