Townsend and glow modes of an homogeneous barrier discharge in helium

In the present time the homogeneous barrier discharge at atmospheric pressure in helium became the object of intensive experimental and theoretical studies. The homogeneous state of the discharge exists also in other gases, however, only the Townsend form is stable. In helium, a glow form by much higher power or a multipeak Townsend form can also be obtained. It is therefore interesting to study theoretically the structure of these regimes, conditions of their existence and the transitions between them. Using a one-dimensional fluid model, two essentially different forms of the homogeneous barrier discharge in helium are simulated. The results of modeling are compared with the experimental data of other authors. The comparison shows good agreement between the calculation and the experiment. The glow mode of discharge is characterized by one current peak of large amplitude per half period. During the breakdown, a spatial structure typical for the glow discharge, consisting of cathode fall, Faraday dark space, positive column, and anode region, develops in the gap. The origin of the this structure differs from that in a DC glow discharge. This formation is mostly the dependence of processes on time. The glow mode is forming at high gap widths and thin dielectric barriers. As the gap width decreases, the discharge transits into the Townsend mode. The primary feature of the weak disturbance of the electric field by spatial charge. The electron density, being much lower than the ion density, increases from cathode to anode. There is no quasineutrality in discharge gap. When the amplitude of external voltage grows, a multipeak Townsend discharge occurs. The formation of several peaks is caused by a small number of initial electrons. A certain initial current however must exist, the only mechanism of its production is the thermodesorption. The stability of discharge shows that a large number of initial electrons is not a necessary condition of the Townsend discharge