Executive Summary : | Expanding plasmas are interesting as they are naturally occurring phenomena, observed in the North and South Pole of our planet Earth (i.e., aurora borealis), where ions are accelerated by the double layers (a potential structure in the plasma consisting of two layers of opposite electrical charge) formed due to plasma expansion by the Earth’s diverging magnetic field. It is proposed that a similar kind of structures can be formed in the laboratory and research will be conducted to understand the cause behind their formation and ways to control their potential height. Conventional plasma sheath theory predicts that there will be a maximum double layer potential height which is ~ 5Te for Argon plasma, as there is no energy source larger than ~ 5Te, where Te is the electron temperature in eV. However, energetic electrons in the source overcoming the potential height can be the energy-source for the double layer, if they neutralize the ion beam accelerated by the double layer. The aim of this research proposal is to study to find an experimental technique to verify the formation of stronger double layers beyond the strength predicted by the conventional plasma sheath theory. Key to this problem is to control electron energy distribution function, as it has a strong correlation with the double layer strength. Therefore, controlling the electron energy distribution is important to make any change in the double layer potential height. Various experimental schemes including auxiliary ion/electron sources have been proposed to inject ion/electron beams into the primary radio-frequency produced plasma, to control the electron energy distribution function. A model will be prepared to study the dependence of the double layer strength with the electron energy distributions. Double layers are interesting because of its application in the electric propulsion thruster. However, the challenge to make it efficient remains unresolved due to lack of understanding the correlation between the double layer and the electron energy distributions. This research is significant because it will not only improve the understanding about the double layers but will identify ways to control the double layers and the associated ion beam energies. |