This study investigates the influence of high energy electrons on the negative ion density along with the effect of filament current, discharge voltage, pressure, and magnetic filter field strength by carrying out measurements of negative ion density in a hot cathode discharge system in the double plasma device using a Langmuir probe technique. In the volume production technique, negative ions are formed by the dissociative attachment of low energy electrons to metastable hydrogen molecules and among the negative ion loss mechanisms; the presence of high energy electrons in the plasma is one of the important factors. Although the magnetic filter could reduce the temperature of the electrons in the target region considerably, high energy electrons were still present in the diffusion region, which could reduce the negative ion density. Negative hydrogen ion density measured by using Langmuir probe in the target region is also compared with the particle balance model considering the set of reactions involved in the production and destruction of negative ions, and a reasonably good match between them has been observed.
The Helicon Plasma Source (HeliPS) designed and developed at the Centre of Plasma Physics-Institute for Plasma Research is a versatile helicon plasma device, which operates in a wide range of magnetic field configurations from 50 G to 500 G. This device is dedicated to perform a broad range of research activities. The main objective for development of the HeliPS is to carry out studies on ion-ion plasmas in electronegative gases. In the near future, ion-ion plasmas will be formed in electronegative gases in the downstream of the plasma production region. Although the system is primarily designed to carry out ion-ion plasma experiments, the same system can also be used for experimental studies on some basic helicon plasma properties such as wave propagation, wave coupling, and plasma instability. At present, argon plasma is produced with a RF power supply of 13.56 MHz frequency. External circuit parameters, such as antenna current, plasma resistance (R), and internal parameters, such as electron density and temperature, are measured. The details of the experimental setup development, device characteristic, as well as preliminary plasma production and characterization to confirm occurrence of the helicon plasma in the system are presented in this article.
In this paper, the effect of mixing of argon and oxygen gas on the mode transition and negative ion production in the helicon discharge is investigated. In the source chamber of the experimental setup, argon–oxygen gas mixture plasma is produced by applying RF power from 100 W to 2000 W at an applied magnetic field of 0.03 T. In this experiment, the total flow rate is kept at 200 SCCM, corresponding to the working pressure of 4–5 × 10−1 Pa. The mode transition to helicon discharge is investigated by varying the concentration of these two gases. To the best of our knowledge, the literature survey indicates this to be the first study of the influence of the mixing of oxygen–argon gas on the mode transition from the inductive to the helicon mode. It is observed that an increase in the concentration of oxygen gas in the discharge shifts mode transition toward higher RF power values, indicating the influence of the nature of the working gas on the transition to the inductive as well as to the helicon mode. The variation of the electron density and temperature is explained in terms of particle and power balance equation. In the source and in the downstream expansion chamber, the effect of the concentration of argon gas on the negative ion production in oxygen discharge is also studied, and the results are explained in terms of various reactions involved in the production and loss of negative ions.
In this work, different plasma parameters, such as electron density, temperature, and negative ion density are measured in both the source and expansion chamber of the Helicon Plasma Source (HeliPS) in a radio frequency (RF) oxygen discharge of 13.56 MHz and are compared with the values obtained numerically using the volume-averaged global model. For this purpose, the global model of RF oxygen discharge suitable for the HeliPS having two chambers (source and expansion) together with the electromagnet in the source chamber and the magnetic cage in the expansion chamber to reduce the radial loss of plasma is developed using the particle and power balance equations. In this model, the radial confinement by the axial field of the electromagnet in the source chamber and the confinement in the expansion chamber by the cusped field of the magnetic cage is incorporated. Studies on the charged particle dynamics by both the model and the experiment show comparable values of the variation of species density and electron temperature with RF power and working pressure as well as with the applied magnetic field of the electromagnet in the source chamber.
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