Role of controlled leak to trigger negative differential resistance in parallel plate glow discharges

-In the current (I) - voltage (V) characteristics of coaxial DC discharge, negative differential resistance (NDR), associated with hysteresis have been observed by varying the control parameter (DC bias voltage). The onset of the NDR has been observed in a DC filamentary discharge with variation of discharge parameters such as discharge voltage, gas pressure and filament temperature. The orientation of magnetic field can also play a significant role in the threshold condition for appearance of the NDR. M. Agop et al. has observed NDR formation in a plasma diode using an auxiliary bias electrode and correlated with the formation of complex structure at this electrode. Although the NDR has been studied from different perspectives, the role of boundary wall in triggering the NDR has not been investigated yet to the best of our knowledge, especially the comparison of the effect of a dielectric boundary with respect to that of a conducting boundary. This paper reports the characterization and investigation of NDR while changing the boundary enclosure of the discharge. The experimental setup consists of a cylindrical SS chamber having two symmetric electrodes (anode and cathode) separated by a distance of 35 mm. The electrode system was covered by dielectric boundaries using a glass tube and mica discs to change the boundary condition of the discharge, viz. from a fully exposed (FE) conducting SS chamber wall to a fully covered (FC) dielectric glass wall. When the discharge was partially exposed to the SS vacuum chamber by making a gap between glass tube and mica disc, an NDR appears in the I-V characteristics which is not observed in for both FC and FE condition. Plasma characterization by Langmuir probe has revealed a higher plasma potential (V_p) with two electron temperature (T_e) in FC condition whereas single T_e with lower V_p has been observed in FE configuration. The details of the characterization of plasma between the electrodes and its role in appearance of NDR in parallel plate DC glow discharge will be presented in the conference. (author)