An electronic, adjustable-waveform spark source for basic and applied emission spectrometry

A conceptually new type of electronic spark source is described. A parallel combination of a hydrogen thyratron and a diode is used as the switch element. The switch operates by providing parallel paths for current oscillating from capacitors discharging through inductive loads. The same principle is used to route current through the analytical spark gap. Either the switch current or the spark current can be adjusted in waveform from fully oscillatory to fully unidirectional simply by changing the value of a single inductor, without changing capacitance, resistance, or the voltage at which the source operates.The electrical circuitry is singularly simple, thus producing a source that is characterized by reliable, long term operation, precise ignition with low time jitter (ca. 5 nsec) and low conducted or radiated radio-frequency interference. Because of the latter, modern electronic devices (such as microprocessors and minicomputers) can be used in conjunction with and in direct control of the spark source, i.e., while the spark is conducting current. The source functions equally well for industrial spectrochemical analysis and for basic research on optical emission phenomena.A partial circuit analysis is included here. The current commutation between the hydrogen thyratron and shunt diode is characterized. Electronic circuitry appropriate for source operation at variable repetition rate is described. The types of spark current waveforms that can be obtained under electronic control are illustrated.