Optical emission patterns and microwave field distributions in a cylindrical microwave plasma source

A cylindrical high density (10¹² cm^?3) large volume (32 cm in diameter and 50 cm in length) homogeneous argon plasma has been produced by a microwave with a frequency of 2.45 GHz and a power of 900 W without a magnetic field. The plasma source is based on a ring shaped rectangular waveguide with eight equally spaced slots in its inside wall. Several optical emission patterns are observed on different conditions and the microwave field is measured by a movable antenna, which showed a clear relationship between the optical emission patterns and the electron field distributions. A mode transition, from a TE_8j mode to a TE_16j mode, occurs when the gas pressure increases from 660 to 1000 Pa. And there is an optical emission pattern when the microwave power decreases from 900 to 300 W. All these phenomena are described in detail and analyzed according to the interactional theory of electrons in plasma with microwave.