Gain characteristics of a microchannel plate operated in the reflection mode for low-energy positive ions

Abstract

Fundamental gain characteristics of a microchannel plate (MCP) operated in the reflection mode for low-energy (20–300 eV) positive ions were studied experimentally in detail. When a MCP with zero-bias angle was used, the gain in the reflection mode increased by about two orders of magnitude compared with that in the conventional transmission mode. Such a remarkable high gain supports the automatic preacceleration effect on incident ions suggested previously and also shows practical usefulness of this operation mode as a simple detector of low-energy positive ions. The reflection mode gain was also found to be highly sensitive to the ion’s incident angle and collector voltage. This suggests that the reflection mode has two additional functions: that of analyzer of the incoming ion’s direction and discriminator of incident ion energies. These properties can be explained in terms of the penetration depth of incident ions into the microchannels, which is the most important factor in this detection technique.