NEGATIVE DIFFERENTIAL RESISTANCE, OSCILLATIONS AND CONSTRICTIONS OF LOW-PRESSURE, LOW CURRENT DISCHARGES

A brief review is given of the recent experimental and theoretical stu dies of low current diffuse discharges. Two models are developed, one that is based on phenomenological description by effective discharge c ircuit parameters and the other which is based on the calculation of t he field profile from the ion distribution for uniform field. In the f irst case the physical process responsible for the development of the negative differential resistance is the dependence of the secondary el ectron yield on current through modification of the field close to the cathode. Experimental systems were developed to provide observables t hat include: breakdown voltage. voltampere characteristics (which in t he low current limit is represented very well by a negative differenti al resistance), limits and the profile of the low current oscillations , frequency and damping of the induced oscillations, current growth co efficient and the onsets for constrictions. All of the observables are very well predicted by the theory based on the data taken from indepe ndent sources, once the steady state secondary electron yield has been fitted to predict the breakdown voltage.