Time-of-flight analyzer of the plasma mass-to-charge composition with a secondary electron multiplier

Abstract

Time-of-flight analyzers of the mass-charge composition are widely used to study plasma generated by discharges of various types. Usually, a Faraday cup is used in the analyzer to measure the ion current. However, in some cases, especially when studying low-current gas discharges, the sensitivity of the analyzer is not enough to accurately record all mass-charge groups of ions in an ion beam. This problem can be solved by using more sensitive ion current detectors, for example, a secondary electron multiplier. In this paper, we compare measurements of the mass-charge composition of a vacuum arc discharge plasma with aluminum, copper, titanium, molybdenum, tantalum, and bismuth cathodes, with an arc current of hundreds of amperes at a pulse duration of hundreds of microseconds using a time-of-flight analyzer using as a sensor, a Faraday cylinder or a secondary electron multiplier. It is shown that the difference between the measurements using the Faraday cup and the secondary electron multiplier is only a few percent, which is an acceptable measurement error. It is determined that the secondary electron multiplier in all cases gives a smaller signal for ions of high charge states than the Faraday cup. An explanation of this difference is given.