A new millimetre-wave method for determination of electron-density profiles in a linear discharge

The method depends on probing the plasma column with a microwave beam incident obliquely on its boundary. Owing to electron-density gradients, the beam is continuously refracted inside the plasma column and finally emerges at a certain point on its boundary, where it is received. The position of that point for any particular angle of incidence can be related to the electron-density profile through a simplified theoretical model which is based on geometrical optics. According to this model, the determination of profile requires measurements at two angles of incidence. The experimental work was carried out on a linear pinched discharge at wavelengths of 8.9 and 4.3mm. The discharge took place in argon at a pressure of 23¿mHg using a capacitor-bank voltage of 6kV and an-energy of 3600J. Electron-density profiles could be determined during the afterglow period of the discharge. It was not possible, however, to determine profiles during the pinch owing to insufficient time resolution.