The design of a microwave plasma cavity

The design of an efficient microwave plasma source is described. This source consists of a quartz tube surrounded by a cylindrical variable-length cavity which is connected to a 2.450-GHz power microwave source. The circuit performance of the plasma-cavity system is qualitatively explained and the lossy plasma-cavity eigenfrequencies are computed as functions of plasma density, effective collision frequency, and cavity length. Experiments demonstrate that a variable high-density plasma with densities in excess of 1000 critical densities can be sustained. Furthermore, by adjusting cavity length and coupling, microwave plasmas can be sustained in flowing and nonflowing argon gaseous environments from pressures of several microns to over one atmosphere.