| dc.description.abstract | The advancing technology of power circuit breakers has led the way for the study of arcs in gas?filled as well as vacuum circuit breakers. The spectroscopic investigations of such arcs have clearly shown the presence of metal vapour like copper, aluminium, lead etc., obviously released from the electrode surface. In the analysis of such arcs and their characteristics, it is essential to have a sound knowledge regarding the electrical discharge properties of these metal vapours.
Secondly, high?power pulsed metal?vapour lasers are gaining popularity because of their high power and efficiency, and as such metal vapours are considered to be the source of high?power radiation. In order to facilitate this, a clear knowledge of the electrical discharge phenomena in metal vapours is essential.
On the other hand, the study of the breakdown and post?breakdown phenomena in metal vapours has resulted in various practical applications such as arc valves, lamps for highway illumination, ion thrusters for rocket propulsion etc.
No doubt, the study of metal vapours such as copper, aluminium etc., are of great importance in many fields, but the generation of these metal vapours, monitoring their pressure, introduction of the electron source and the electrodes into the constant vapour?pressure zone pose difficulties since it involves high working temperatures (>1000°C!). This could be made easier if experience is gained with the handling and study of low?temperature metal vapours.
With this in view, the present work was initiated. A special heat?pipe apparatus was fabricated and stable sodium vapours were successfully generated, controlled and monitored.
This thesis deals with the breakdown and post?breakdown studies in sodium vapour using coaxial cylindrical electrode configuration with a constant inter?electrode spacing of 5 mm. Breakdown potentials and V–I characteristics have been obtained in sodium vapour over a pressure range of 0.2 to 6 Torr (0.02 – 0.6 kPa).
The theories of breakdown, the earlier work in metal vapours and their applications in the fields of engineering and laser physics have been reviewed. Also, a brief review of the theoretical estimation of ? and breakdown voltages has been made (Chapter 2).
Chapter 3 outlines the heat pipe, its origin, design, construction, working principles and its application in various fields including the latest development.
A detailed description of the experimental set?up and the experimental techniques etc., have been described in Chapter 4.
In Chapter 5, the discussion on the experimental results and the theoretical evaluations have been presented.
The observed breakdown voltages in sodium vapour show a trend of saturation beyond the pd value 0.18 kPa·cm. The V–I characteristics show a strange pressure dependency. Also, a negative current is observed with a positive potential applied across the gap.
The theoretical calculations are made using the ionization cross?section and the drift velocities measured in sodium vapour for uniform fields.
A summary of the results obtained and the important conclusions made therefrom and the scope for further studies in this area of work are the contents of Chapter 6. | |
