Modelling of the homogeneous barrier discharge in helium at atmospheric pressure

Abstract

Numerical calculations of spatio-temporal characteristics of the homogeneous barrier discharge in helium are performed by means of a one-dimensional fluid model. The influence of the elementary processes on the discharge behaviour is studied by variation of the corresponding rate constants. The simulation and the analytical interpretation are carried out for two basic modes of the homogeneous barrier discharge, i.e. the Townsend and glow modes. The Townsend discharge is characterized by the absence of quasineutral plasma; several current peaks may occur during the half-cycle. The oscillations of the current are caused by a lag between the ion production nearby the anode and the subsequent ion–electron emission on the cathode. The specificity of the glow discharge is the development of a cathode region and a positive column during the breakdown, as well as the presence of quasineutral plasma in subsequent phases. The positive column occurs because the shielding of the external field by the plasma is not instantaneous. The dependence of the discharge behaviour on the external parameters, such as the amplitude and frequency of the applied voltage, discharge gap width, and thickness of dielectric barriers, is analysed. The mode of the discharge is governed mostly by the gap width and barrier thickness and depends weakly on the amplitude and frequency of the applied voltage. As the barriers are thin and the discharge gap is sufficiently wide, the glow mode occurs; otherwise, the discharge is Townsend.

Fluid model for a partially packed dielectric barrier discharge plasma reactor

“…At a higher frequency, 60 kHz, the current profile exhibits a sinusoidal shape, much different from the standard pulse-like waveform observed for atmospheric DBDs. 38 Such a distinct difference in current profiles at higher frequencies has been observed before 43,44 and has been attributed to the constant production of charged particles due to continuous existence of excited species at higher frequencies. 44 On inclusion of partial packing, discharge current profile [ Fig.…”

“…This is expressed in the current signal in the form of a peak. Multiple peaks occur due to multiple breakdown in a single voltage cycle, 38,45 which can happen if the gap voltage crosses the breakdown voltage more than once in one cycle. Large accumulation of charges increases the external voltage significantly, making multiple breakdowns feasible.…”

“…Helium has a relatively simpler plasma chemistry, low breakdown voltage, and ionizes easily to form a stable homogeneous glow discharge, which is easier to simulate using a fluid model, as opposed to the filamentary discharge typically observed with molecular gases. 4,38,39 These factors further help in reducing the model size and the computational cost, thereby providing more leverage in performing a longer study over more periods of applied potential such that stable behaviour can be studied. It should be noted that the difference in discharge performance between helium and molecular gases also limits the applicability of the current model.…”

Nonlinear frequency coupling in dual radio-frequency driven atmospheric pressure plasmas

“…Nitrogen impurities have been found to be of major importance, since Penning ionization by metastable excited particles is a crucial ionization mechanism under ambient pressure conditions. 19 Eight species, namely, neutral helium ͑He͒, excited helium ͑He ‫ء‬ ͒, excited helium molecules ͑He 2 ‫ء‬ ͒, helium positive ions ͑He + ͒, helium molecular ions ͑He 2 + ͒, nitrogen ͑N 2 ͒, nitrogen ions ͑N 2 + ͒, and electrons ͑e͒ are considered. The secondary electron emission coefficient ␥ is set to 0.25 for helium species and 0.005 for nitrogen ions.…”

Characteristics in the jet region of helium radio-frequency atmospheric-pressure glow discharge with array generators

“…Seven species involved in thirteen chemical reactions are considered as listed in Table I, [20][21][22][23][24][25][26] including electrons (e), helium metastables (He * , He * 2 ), helium ions (He + , He + 2 ), nitrogen molecules (N 2 ) and nitrogen molecular ions (N + 2 ). The number density of helium atoms (He) is assumed to be constant and determined by the ideal-gas law since its number density is much higher than those of the other species.…”