Determination of effective electron yield from swarm and time delay measurements

¹ Department of Physics, University of Niš, PO Box 224, 18001 Niš, Yugoslavia
² Institute of Physics, PO Box 57, Belgrade, Yugoslavia

Corresponding author: vidosav@pmf.pmf.ni.ac.yu

Received: 22 August 2000
Revised: 6 February 2001
Accepted: 8 February 2001
Published online: 15 June 2001

Abstract

In this paper the dependence of the effective secondary emission coefficient-effective electron yield γ_eff in nitrogen on the reduced field (the ratio of the electric field and the gas density E/N) for various cathode surfaces is determined. Two different methods are applied: swarm measurements (from breakdown voltage) and time delay measurements. In the latter technique, first the breakdown probability is determined as a function of voltage and then γ_eff is derived from it. The results of applying both methods are in good agreement for the γ_eff versus E/N dependence. The measurements were made for copper cathode, untreated and treated by gas discharge and also several thousand electrical breakdowns, gold-plated copper and steel cathodes. Secondary electron yield γ_eff is of the order of a few percent at moderate and high E/N, and slightly increases with increasing E/N up to several kTd. At low E/N, a characteristic peak appears (at about 600 Td for copper). The γ_eff value increases when copper cathode is treated by gas discharges and becomes stable after several thousand breakdowns, agreeing well with other breakdown results in the literature. The chosen values for the Townsend primary ionization coefficient, obtained from best fits to available experimental data in the literature and the choice of the equilibration distance from the cathode significantly influence determination of γ_eff. Finally, our results are compared with the results of other authors for different cathode materials and a good agreement is found.