Electron-drift velocity determination in CF4 and SF6 in a strong electric field from breakdown curves of low-pressure RF discharge

In this paper we report the values of the electron-drift velocity in CF4 and SF6 within the range E/p = 200–1000 V cm−1 Torr−1. We have used the recorded coordinates of the turning point on the breakdown curves of the rf capacitive discharge. We have also formulated the main requirements to the experimental device for correct recording of the breakdown curves of the low-pressure rf capacitive discharge. Our data are in good agreement with those of other authors who have used different approaches. We have also obtained the results on the electron-drift-velocity values within the E=p region where no other techniques are applicable. Our findings are also supported by numerical simulation data obtained with the application of a conventional Bolsig code

Validating the collision-dominated Child–Langmuir law for a dc discharge cathode sheath in an undergraduate laboratory

In this paper, we propose a simple method of observing the collision-dominated Child–Langmuir lawin the course of an undergraduate laboratorywork devoted to studying the properties of gas discharges. To this end we employ the dc gas discharge whose properties are studied in sufficient detail. The undergraduate laboratory work itself is reduced to registering the voltage drop across the electrodes, the discharge current as well as the cathode sheath thickness. We can easily perform the measurements of all three quantities with sufficient accuracy in a laboratory equipped with vacuum pumps

Alpha–gamma transition in RF capacitive discharge in low-pressure oxygen

We report the recorded current–voltage characteristics of a RF capacitive discharge in oxygen. Low-frequency oscillations of the plasma potential in a kilohertz frequency range are observed to accompany the transition of the discharge from a weak- (a-) to a strong-current (g-) regime in the low-pressure range. The weak-current regime of the RF capacitive discharge is observed within the pressure range limited not only from the medium pressure side but also from the lower-pressure one. Electron temperature and plasma density are registered with a probe technique

Double layer onset inside the near-electrode sheath of a RF capacitive discharge in oxygen

This paper reports the axial profiles of the electron temperature Te in the RF capacitive discharge in oxygen recorded with a probe technique. We observed the Te peaks near the boundaries of the sheaths as well as inside the near-electrode sheath. The Te peak inside the sheath is, probably, due to the formation of the double layer at the anode phase of this near-electrode sheath. The assumption of a double layer formation is also supported by the photos of the sheath glow making evident the bright region inside the sheath. The results of our measurements agree with our fluid simulation satisfactorily

Rf breakdown of low-pressure gas and a novel method for determination of electron-drift velocities in gases

This paper reports the results of the detailed and comprehensive experimental and theoretical treatment of the rf gas breakdown. We give the measured breakdown curves of the low-pressure rf discharge in argon, hydrogen and air in a broad range of gas pressures and interelectrode distances. The different processes of generation and loss of charged particles participating in the rf gas breakdown are discussed. We suggest to distinguish the following sections on the rf discharge breakdown curves: multi-pactor, Paschen, diffusion-drift and emission-free ones. The analytic gas breakdown criterion of the combined (rf plus weak dc electric field) discharge taking into account the anisotropy of electron diffusion in the electric field is obtained. A novel method for determining the electron-drift velocity from the measured rf breakdown curves is suggested. The electron-drift velocity data in argon, hydrogen and air obtained with this technique in the range E/p = 50–2000 V cm−1 Torr−1 are given and compared with those got by conventional means

Scaling Law for a Low-Pressure Gas Breakdown in a Homogeneous DC Electric Field

Gas breakdown in nitrogen, air, and oxygen in a dc electric field at various interelectrode distances L is studied experimentally. A scaling law for a low-pressure gas breakdown Udc=f(pL,L/R) is deduced. According to this scaling law, the breakdown voltage Udc is a function not only of the product of the gas pressure p and the gap length L, but also of the ratio of the gap length L to the chamber radius R. It is shown that, for any dimensions of the cylindrical discharge chamber (in the range of L/R under investigation), the ratio of the breakdown electric field to the gas pressure p at the minimum of the ignition curve remains constant: (Edc/p)min = const. A method for calculating the ignition curve in a cylindrical discharge chamber with arbitrary values of L and R is proposed

Experimental Study of a Low-Pressure Glow Discharge in Air in Large-Diameter Discharge Tubes: I. Conditions for the Normal Regime of a Glow Discharge

The initiation and characteristics of a low-pressure glow discharge in air in large-diameter discharge tubes are studied. A deviation from the Paschen law is observed: the breakdown curves Udc(pL) shift toward the higher values of Udc and pL as the interelectrode distance L increases. It is shown that the normal regime of a glow discharge is accompanied by gas ionization in the anode sheath. This takes place only for pL values lying to the right of the inflection point in the breakdown curve. The cathode-sheath characteristics in the normal and abnormal regimes of an air discharge for a duralumin cathode are determined. The axial profiles of the ion density, electron temperature, and plasma potential, as well as the anode voltage drop, are measured at various air pressures

Radial structure of low pressure rf capacitive discharges

This paper studies the glow intensity distribution of the discharge plasma against the tube radius and reports the radial profiles of electron temperature and plasma concentration in the rf capacitive discharge registered with a Langmuir probe. An abrupt increase of electron temperature and glow intensity near the tube wall in the weak-current a-mode of the rf capacitive discharge is revealed, the radial distribution of plasma concentration and ion flow to the electrodes possessing a maximum near the radial sheath boundary. In the g-mode of the rf capacitive discharge the electron temperature decrease in the total plasma volume leads to an electric field weakening and the peak of the glow intensity near the tube wall vanishes. The radial sheath thickness in the a-mode of the rf capacitive discharge obtained with 2D simulation experiences pulsations during the rf field period, the changing radial electric field heating electrons and increasing the plasma concentration near the boundary of the radial sheath

Longitudinal combined discharge extinction in low pressure nitrogen

This paper reports the registered extinction curves of the longitudinal combined discharge in nitrogen when rf and dc voltages were applied to the same electrodes. The application of dc voltage is shown first to lead to an increase in the rf discharge extinction voltage; at the same time, the ‘‘cathode’’ sheath thickness increases and the number of charged particles in the plasma volume decreases. The discharge extinction curve first shifts to the range of higher rf voltage and gas pressure values, and the region of multi-valued dependence of the rf extinction voltage on gas pressure vanishes. At larger dc voltage values, when the ‘‘cathode’’ sheath breakdown occurs, the rf discharge extinction voltage decreases and approaches zero at the dc extinction voltage for the dc self-sustained discharge

Modes of longitudinal combined discharge in low pressure nitrogen

This paper reports the modes of a low pressure discharge in the combined (rf + dc) electric field. We propose to distinguish three modes of a longitudinal combined discharge (rf and dc voltages were applied to the same electrodes): (1) a non-self-sustained rf discharge perturbed by a dc electric field, (2) a combined discharge and (3) a non-self-sustained dc discharge perturbed by an rf electric field. The existence conditions of these modes are determined. The parameter range in which the first mode of the combined discharge may be extinguished via increasing dc voltage is shown to be limited with an rf discharge extinction curve from the low pressure side as well as with a curve of the least rf voltage corresponding to the transition of the combined discharge from the first mode to the second one. The relation between the thicknesses of the ‘cathode’ and ‘anode’ near-electrode sheaths is derived analytically for the first mode, which is in good agreement with experimental data