In this work, diagnostics and comparative analysis of microhollow cathode discharges with an open and covered external surface of the cathode in helium at atmospheric pressure were carried out. It is shown that by covering the external surface of the cathode, it is possible to achieve the effect when the current–voltage characteristics of the discharge grows in a wider range of discharge currents. Obviously, in this case, the negative glow (NG) plasma of the hollow cathode occupies a significant part of the discharge cell, as evidenced by the measurements carried out with the additional electrode. The electron temperature values determined from the I–U characteristic of the additional electrode are 0.3–0.4 eV for a microhollow cathode discharge with a covered external surface, which indicates that the plasma of such discharge is similar to NG plasma of glow discharge. The fast parts of the second derivatives of the I–U characteristic of the additional measuring electrode demonstrate the detection of the spectra of fast electrons produced as a result of Penning ionization reactions. Moreover, by covering the external surface of the cathode, conditions are created under which the entire discharge volume is occupied by a NG plasma, which makes it possible to achieve a better resolution for recording the spectra of fast electrons.

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A self-consistent extended fluid-dynamic model describing a focused microwave discharge in a molecular gas is developed, and numerical simulations of the formation of plasmoids in nitrogen in an experimentally operating cylindrical paraboloid focusing system are carried out. It is shown that, depending on the input power and gas pressure, plasmoids ranging from one to four can be formed. The main spatial–temporal parameters of the plasmoid formed at the main focus of the system are studied in the active phase and in the afterglow phase. The main channels of gas heating in the domain of plasmoid formation are investigated. The importance of taking into account gas heating in the self-quenching reactions of excited nitrogen molecules, both in the active phase and in the first microseconds of the afterglow phase, is shown. The main mechanism at long times in the afterglow phase is the release of energy in vibrational–translational relaxation.

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