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

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

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

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

Electron drift velocity in N2O in strong electric fields determined from rf breakdown curves

We report measurements of the breakdown curves of an rf capacitive discharge in low pressure nitrous oxide. The electron drift velocity was determined from the locations of the turning point and of the minimum in the breakdown curves in the range E/p = 87–840 Vcm−1 Torr−1. We compare our results with values calculated from the published cross-sections in the range E/p = 1–5000 Vcm−1 Torr−1 and find good agreement

The Effect of Discharge Chamber Geometry on the Characteristics of Low-Pressure RF Capacitive Discharges

We report the measured extinction curves and current–voltage characteristics (CVCs) in several gases of RF capacitive discharges excited at 13.56 MHz in chambers of three different geometries: 1) parallel plates surrounded by a dielectric cylinder (“symmetric parallel plate”); 2) parallel plates surrounded by a metallic cylinder (“asymmetric confined”); and 3) parallel plates inside a much larger metallic chamber (“asymmetric unconfined”), similar to the gaseous electronics conference reference cell. The extinction curves and the CVCs show differences between the symmetric, asymmetric confined, and asymmetric unconfined chamber configurations. In particular, the discharges exist over a much broader range of RF voltages and gas pressures for the asymmetric unconfined chamber. For symmetric and asymmetric confined discharges, the extinction curves are close to each other in the regions near the minima and at lower pressure, but at higher pressure, the extinction curve of the asymmetric confined discharge runs at a lower voltage than the one for the discharge in a symmetric chamber. In the particular cases of an “asymmetric unconfined chamber” discharge or “asymmetric confined” one, the RF discharge experiences the transition from a “weak-current” mode to a “strong-current” one at lower RF voltages than is the case for a “symmetric parallel-plate” discharge

Modes of low-pressure dual-frequency (27/2 MHz) discharges in hydrogen

This paper studies the modes of dual-frequency (high-frequency (HF)/low-frequency (LF)) low-pressure discharges. The dual-frequency discharges are shown to burn in one of three possible modes. At small LF voltages the first mode is observed, i.e. the HF discharge perturbed by the LF voltage. The second mode, i.e. the combined discharge, exists in the presence of intense ionization in the sheaths, when the LF voltage exceeds some critical value. The third mode (the LF discharge perturbed by an HF field) is observed when a small HF voltage is applied to the burning LF discharge. The range of parameters within which the first mode of the combined discharge may be extinguished by the LF voltage increase is shown to be limited by the HF discharge extinction curve from the low-pressure side as well as the lowest HF voltage for the transition of the discharge from the first mode to the second one