A stationary filamentary microwave discharge at a high pressure of argon

A stationary discharge in the form of a filament about 1 mm in diameter is produced in a quartz tube 16 mm in diameter passed through the wider wall of a standard waveguide and field with argon at a pressure of 300 mm Hg at a microwave power of 50 W on a frequency of 7 GHz. The number of filaments increases gradually from one to seven as the power and pressure are increased. The filaments are parallel and oriented along the electric field of the wave. They are arranged symmetrically relative to the equatorial plane of the tube. The distance between the filaments decreases as their number increases. The stationary filaments arising due to ionization-overheating instability may be explained qualitatively using the interference-equilibrium model and assuming that a discharge is organized such as to provide for the maximal power absorption.