Conversion of a multichannel analyser into an analogue signal averager

Williams

1976

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111

Combined spatial and temporal measurements of ionization growth in nitrogen have enabled the secondary ionization effect due to N2(A3 Sigma u+) metastable molecule impact on the cathode to be separated from the overall ionization growth data. The residual data have been analysed by standard methods to give accurate values of the primary ionization coefficient alpha /N within the range E/N=140-3400 Td (1 Td identical to 10-17 V cm-2). This range has been extended down to 85 Td by application of an indirect procedure based on improved knowledge gained from the secondary ionization measurements in nitrogen and their dependences on E/N. The measurements have been able to separate the secondary ionization coefficient into a fast (photon and positive ion) component and a slow (metastable molecule) component.

Section: Temporal Measurementsmentioning

confidence: 99%

Combined spatial and temporal studies of ionization growth in nitrogen

Williams

1976

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111

“…Ionisation currents were measured using a Tektronix (AM 502) preamplifier and where necessary, a signal averager, designed around a multichannel analyser (MCA) (Chapman and Williams 1975). The value of the load resistance used depended on the required frequency response.…”

Section: Experimental Apparatusmentioning

confidence: 99%

Laser-induced optogalvanic effects under prebreakdown conditions in neon

Kravis

1981

A pulsed tunable dye laser has been used to selectively perturb two metastable states 3P2 (ls5 in Paschen notation) and 3P0 (ls3) in the prebreakdown phase of ionisation growth in neon. Optogalvanic signals showing a fast positive spike followed by a slow negative component were recorded and explanations are offered for each phase of the waveform. Combined with observations of temporal growth of current, these signals provide information about the magnitude of the depletion of the metastable particle density. The time evolution of the metastable atom populations are examined theoretically. Experimental and theoretical saturation curves for two optogalvanic signals are compared.

“…One source of asymmetry in the temporal trace is a faulty ultraviolet lamp which has unequal turn-on and turn-off times; this was checked with a photocell at the beginning of each experimental run and the lamp replaced when necessary. A second source of asymmetry is very small squarewave signals which occur at the same frequency as the true signal and which add to or subtract from the real signal during the accumulation needed for signal averaging (see Chapman and Williams 1975). These spurious signals are associated with inadequate earthing but because of their small size are not always easy to detect and control.…”

Section: Secondary Ionisation Eflectsmentioning

confidence: 99%

Investigations of ionisation growth in gas mixtures

McIntosh

1978

Ionisation growth in the gas mixtures, N2:NO, N2:He and CO2:N2:He has been studied using combined spatial and temporal measurement techniques. Observations in N2:NO mixtures confirmed that reliable information about primary ionisation processes could be obtained even in the presence of large secondary surface ionisation processes and extensive studies of the two ternary mixtures CO2:N2:He (1:1:8) and (1:2:3) and one binary N2:He (1:9) mixture have been undertaken. Primary and secondary ionisation coefficients covering the range of values 60