The axial distributions of the optical emission intensity and metastable atom density are shown experimentally for DC and RF helium discharges. Significant differences in the cathode glow adjacent to the cathode sheath are perceived between the DC and RF discharges. These differences seem to lead to differences in the consistencies of their cathode sheaths. It is found that the RF glow is caused by a direct excitation of non-thermalized high-energy electrons; on the other hand, the DC glow is caused by a dissociative recombination of old molecular ions and thermalized low-temperature electrons in addition to the former process. A theoretical model of metastable atoms in the cathode glow region is proposed, and the theoretical curves are compared with the experimental results of metastable density distribution. The validity of this model is then assured, at least qualitatively.

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.

This study presents a novel floating probe method to measure electron temperatures using a hollow cathode-type discharge tube. The proposed method detects a shift in the floating potential when an AC voltage is applied to a probe through an intermediary blocking capacitor. The shift in the floating potential is described as a function of the electron temperature and the applied AC voltage. The floating probe method is simpler than the Langmuir probe method because it does not require the measurement of volt-ampere characteristics. As the input AC voltage increases, the electron temperature converges. The electron temperature measured using the floating probe method with an applied sinusoidal voltage shows a value close to the first (tail) electron temperature in the range of the floating potential.

In the cathode fall region of a glow discharge, where the electric field decreases rapidly with distance from the cathode, parameters for electrons obtained in an equilibrium state can not be correctly used in a theoretical study. In this paper, the cathode region in a normal glow discharge has been analysed by a Monte Carlo simulation. Four types of inelastic collisions together with an elastic collision, the reflection of electrons from electrodes and the back-scattering of electrons to the cathode, were taken into account considering the three-dimensional motions of electrons. Results show that alpha /p (where alpha is the ionisation coefficient and p is the gas pressure) is in good agreement with Friedland's result. Also, the mean energy of electrons in the negative glow region was found to be about 11 eV, which is much smaller than previous values. The difference in spatial distribution of optical emission between singlet terms and triplets was also indicated.

Frequency dependence of electron temperature in hollow cathode-type discharge as measured by several different floating probe methods To cite this article: Shuichi SATO et al 2018 Plasma Sci. Technol. 20 085405 View the article online for updates and enhancements. Related content Floating harmonic probe measurements in the low-temperature plasma jet deposition system M Zanáška, Z Hubika, M ada et al.-Improved RF-driven probe method for RF discharge plasma diagnostics A Ohsawa, M Ohuchi and T Kubota-Effect of finite electrode area ratio on highfrequency Langmuir probe measurements M Shimoyama, K-I Oyama, T Abe et al.