Characteristics of a Channel Electron Multiplier for Detection of Positive Ion

Abstract
The efficiency vs operation voltage characteristics of a channel electron multiplier (CEM) with a negative voltage applied to the entrance cone are investigated in detail. In this negative bias operation, an abnormal increase in efficiency with operation voltage is found, arising from two main mechanisms. One is the change in potential distribution in the cone with the applied voltage. This is because the probability of secondary electrons ejected from the cone being pulled into the channel depends on the potential distribution in the cone. The other is the ionization of particles by leakage electrons from the gap between the CEM exit and the electron collector. Methods of solving these problems are also described.