Magnetic Electron Multipliers for Detection of Positive Ions

Abstract

Two designs of 15‐stage electron multiplier wherein focusing from one beryllium copper dynode to the next occurs in crossed electric and magnetic fields have been developed particularly for detection of weak beams or pulses of positive ions in magnetic fields. One, with dynodes ⅜ in. wide, is usable in fields between about 250 and 460 oersteds while the other, with dynodes ⅛ in. wide, is usable in fields between about 300 and 1100 oersteds. It appears likely that, by using still narrower dynodes, such multipliers can be constructed to operate in fields of several thousand oersteds. Advantages of these designs over previously described multipliers employing crossed fields are the use of about half the number of insulated plates and less tendency, because of uniformity of the electric field, for breakdown and noise, due to ion feedback, to occur. The uniformity of the electric field also allows quite reliable calculation of the spread in transit time. From this it is concluded that, with a modified collecting system, a multiplier could be built with a rise time between 10⁻¹¹ and 10⁻¹⁰ sec, which is very probably less than could be obtained with a static multiplier.