Current wave forms of initial stages of breakdown and corona formation in a short negative point-to-plane gap have been measured with a nanosecond time resolution in air, O2, and N2 at pressures 13.33–100 kPa, and at various overvoltages. The experiments revealed the existence of a stepped form of negative corona Trichel pulses in O2 at atmospheric pressure. To test existing models for the negative corona pulse formation, effects of changing cathode secondary electron emission were studied using a brass cathode coated by CuI and graphite. It is concluded that a negative corona (Trichel) pulse is associated with the ignition of a cathode-directed streamer in the immediate vicinity of the cathode and the subsequent formation of a glow-discharge-type cathode region at the streamer arrival to the cathode. The implications of these results to negative corona applications are discussed.

Time-averaged electric potential profiles in a capacitive-coupling parallel-plate electrode neon gas RF discharge plasma have been investigated experimentally. The experiment was conducted by using 65 mm ID, 45 mm long cylindrical discharge tubes with parallel plate electrodes located outside of the discharge vessel and resting against its cylindrical sides. The time-averaged electric field, plasma density and electron temperature were measured by radially movable electrostatic probes placed in the centre of the electrode. The results show that: (i) the electrical potential profiles of the discharge tubes were observed to be significantly influenced by the RF powers and gas pressures; (ii) an asymmetric potential profile was observed, together with a potential barrier in the central region of the discharge tube; (iii) a large quasi-neutral plasma region was not observed in the current experimental conditions; however, a relatively uniform electric field region was observed for gas pressure p<1 Torr; and (iv) the electron temperature decreased with increasing RF powers and gas pressures.

The plasma parameters in noble-gas narrow-tube and capillary-tube plasmas have been studied experimentally over the pressure (p) range from 0.1 to 10 Torr. Tube inner diameters, 2R, of 0.5 and 0.8 mm (capillary) and 3 mm (narrow) were used in the present investigation, together with axially movable anodes and cylindrical electrostatic double probes for the electric field and the electron temperature measurements, respectively, in noble gases, i.e. He, Ne, Ar, Kr and Xe. The results show that the axial electric field Ez/p and plasma density decrease with increasing pR and the atomic weight of noble gases. No significant tube radius effect has been observed for the axial electric field if one analyses results in terms of pR. The electron temperature decreases significantly with increasing pR for He and Ne, and depends slightly on pR for Ar, Xe, and Kr.

The electron temperature and the axial electric field of a positive column with a transverse magnetic field of 0-500 G are given for helium, neon and argon at a gas pressure of 0.3 to 10.0 Torr with a discharge current of 20-50 mA. Measurements show that the electron temperature and the axial electric field increase considerably with a transverse magnetic field at low gas pressure. These measurements are compared with a theory which takes the electron loss at the wall into account and relatively good agreement is found.

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