Determination of effective electron yield from swarm and time delay measurements

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