The processes of formation and development of spatial non-uniformities of a high-pressure (p = 1 - 4 bar) electrical discharge in a Ne - Xe - HCl excimer gas mixture have been studied experimentally. It has been shown that transformation of the discharge into the constricted state is preceded by the low-current () uniform glow phase. The longitudinal discharge structure which is formed consists of three main regions: a bright cathode sheath glow, dark space and a positive column. A subsequent current increase () leads to local disturbances of cathode electron emission and a change in the discharge structure as a whole. The dynamics of the development of non-uniformities is described as well as its dependence on the discharge driving conditions. It has been demonstrated that the current reversal in the oscillating pumping regime is accompanied by the creation of a depleted zone near a newly formed cathode.

The effect of electrode processes on the spatial uniformity of a self-sustained XeCl laser discharge has been experimentally studied. It has been shown that the longitudinal discharge structure, much as the classical one, is formed towards the end of the pre-breakdown stage. The primary disturbances of the uniform discharge structure have been observed during the formation stage at a current density of about 1-10 A cm-2. It was supposed that non-local effects play a part in discharge filamentation. The effect of the rate of increase of current on the development of the discharge instabilities has been revealed.

Numerical study of a self-sustained low-pressure (6.8 Pa or 50 mTorr) wire discharge in helium is reported. The current-independent voltage drop across the cathode sheath is found to be of ∼250 V. The other part of the discharge voltage is essentially applied across the anode sheath. It drains electrons from the quasi-neutral plasma and thus presents a necessary condition for discharge maintenance. Two major groups of electrons have been distinguished: the fast electrons of ∼(24-250) eV, as well as a very small fraction of hot (run-away) electrons with the energy close to the discharge voltage, are responsible for gas ionization throughout negative glow while the thermalized electrons of ∼1's eV are easily captured by the anode and so removed from the discharge.

A pulsed low-pressure wire discharge was studied experimentally. One can clearly distinguish at least three very different phases in the discharge development. During the breakdown lag the ionization takes place principally near the wire anode. The cathode secondary emission under ionic bombardment begins to play a (minor) role throughout the low-current non-steady-state phase since the cathode sheath is not yet formed. Once the sheaths are formed, the hollow-cathode discharge develops. The stability of a hollow-cathode discharge with an immersed small-size wire anode was analyzed. It is shown that the ratio of electrode surfaces Scathode∕Sanode necessary for uniform discharge formation depends on secondary emission yield, the nature of gas, and anode geometry. If the stability condition is violated, a double anode sheath appears and discharge becomes unstable.

No abstract

No abstract

Electrical and thermal properties of a single electrode configuration corona discharge generated under radiofrequency high voltage inside an open air gap at pressures above 1 bar is investigated. Time-resolved imaging of the discharge shows a four-step development of the discharge at atmospheric pressure starting by streamers' inception and propagation, evolving in heating waves and stabilizing in a stationary regime until the power supply is switched off. The mean gas temperature reaches about 1700 K in tens of microseconds with electrical energy release around tens of millijoules. Heating has been attributed to ion collisions and excited species relaxation, promoted by the successive time periods of the power supply. At higher pressures, beyond 3 bar, this behaviour changes and heating occurs at the same time as the discharge propagates. It leads to hot channels which constrict near the electrode as long as the voltage pulse is applied. Temperature gets higher and saturates at 2600 K whatever the voltage and the pressure. Considering the change in the electrical energy density released within the plasma channels with pressure and voltage, temperature saturation seems to be an effect of heat confining within the channels due to pressure. The large and non-thermal plasma generated by the RF corona discharge is a very good candidate for car engine lean mixtures ignition issues.

No abstract