Gain of windowless electron multipliers 226EM and EMI 9643/2B for highly charged Ta ions

The gain of windowless electron multipliers 226EM and EMI 9643/2B with BeCu dynodes was measured for Taq+ ions (12 less than or equal to q less than or equal to 49) with kinetic energies ranging from 8 to 164 keV/q. A Faraday cup was used as a standard ion-current detector. The comparison of the anode current of an electron multiplier (EM) with the Faraday cup current initiated by impact of ions indicates effects of their charge state as well as the velocity for response of both the EMs. The current gain of both the EMs has been found to monotonously increase with increasing charge state for ion energy per charge up to 24 keV/q but has a minimum for higher energy. The analog particle gain derived from the measured current gain increases with increasing charge state for all the accelerating voltages applied. The analog particle gain of 226EM increases with increasing ion energy per charge for q less than similar to 27 but decreases with ion energy for higher q. For EMI 9643/2B the particle gain increases with increasing velocity up to charge state 49 where it becomes approximately independent of its velocity. (C) 1997 American Institute of Physics.