Striations in moderate pressure dc driven nitrogen glow discharge

Abstract

Plasma stratification has been studied for more than a century. Despite the many experimental studies reported on this topic, theoretical analyses and numerical modeling of this phenomenon have been mostly limited to rare gases. In this work, a one-dimensional fluid model with detailed kinetics of electrons and vibrationally excited molecules is employed to simulate moderate-pressure (i.e. a few Torrs) dc discharge in nitrogen in a 15.5 cm long tube of radius 0.55 cm. The model also considers ambipolar diffusion to account for the radial loss of ions and electrons to the wall. The proposed model predicts self-excited standing striations in nitrogen for a range of discharge currents. The impact of electron transport parameters and reaction rates obtained from a solution of local two-term and a multi-term Boltzmann equation on the predictions are assessed. In-depth kinetic analysis indicates that the striations result from the undulations in electron temperature caused due to the interaction between ionization and vibrational reactions. Furthermore, the vibrationally excited molecules associated with the lower energy levels are found to influence nitrogen plasma stratification and the striation pattern strongly. A balance between ionization processes and electron energy transport allows the formation of the observed standing striations. Simulations were conducted for a range of discharge current densities from ∼0.018 to 0.080 mA cm−2, for an operating pressure of 0.7 Torr. Parametric studies show that the striation length decreases with increasing discharge current. The predictions from the model are compared against experimental measurements and are found to agree favorably.

An improved calculation scheme of electron flow in a propagator method for solving the Boltzmann equation

“…Nevertheless, the method is empirically known to yield good results, and is widely used for its convenience in numerous studies and applications (several examples are cited as references). [6][7][8][9][10] In the general plasma fluid models, swarm parameters obtained by BE analysis under DC electric fields have been usually used even for the simulation of RF plasmas. As another option, it is possible to use the swarm parameters obtained by BE analysis under RF electric fields.…”

Formation mechanisms of striations in a filamentary dielectric barrier discharge in atmospheric-pressure argon

“…For instance, the relaxation of electrons to spatially homogeneous state and different striation modes in collision dominated plasma normalised by pressure have been investigated using a kinetic approach [23][24][25]. Besides this, the majority of theoretical studies have been carried out for low or moderate pressure [22,[26][27][28][29][30][31][32][33][34][35][36], and fewer of them have dealt with discharges at atmospheric or sub-atmospheric pressure [8,19,21,[37][38][39][40][41]. A thorough investigation of the stratification of discharges in inert gases at low pressure (ranging from 5 mTorr to 2 Torr) has been conducted using kinetic or discrete dynamic models [22,[26][27][28][29].…”

“…Apart from the kinetic or discrete dynamic models, fluid and hybrid modelling studies of striations along the positive column in low-pressure discharges in argon and nitrogen have been reported in [30][31][32][33]. Recently, the modelling of the appearance of striations in a nitrogen glow discharge at a pressure of tens of Torrs has been presented [35]. Furthermore, particle-in-cell and fluid models have been applied to describe their occurrence in low-pressure discharges in neon and argon [36].…”

A self-consistent hybrid model of kinetic striations in low-current argon discharges

“…Striations are ionization waves specific to collisional plasmas [1,2]. Studies of plasma stratification remain an area of active research, testing our understating of electron kinetics and plasma chemistry [3,4].…”