Thermal imaging of microwave fields inside the surfatron and the microwave plasma torch

A new method is introduced for imaging microwave fields, such as those found in microwave-plasma support structures. The method relies upon the darkening that such fields cause in heat-sensitive paper, such as that used in some telefax printers. With this new method, the microwave-frequency electric fields inside two microwave-plasma support structures, the surfatron and the microwave plasma torch, have been measured and subsequently imaged in three dimensions. The images reveal that the surfatron and microwave plasma torch have different operational behavior. As expected, the electric field strength inside the surfatron exponentially falls off down the length of the quartz plasma tube. The field inside the microwave plasma torch initially diminishes, but then increases in strength towards the end of the tube. An aerosol was introduced into the surfatron to observe the effect of water vapor on the electric field strength and distribution. The exponential axial decay of the electric field in the ‘dry’ surfatron plasma, characteristic of a surface wave propagating down a quartz plasma tube, is extended further down the quartz tube in the ‘wet’ plasma. A drop in plasma conductivity is likely the origin of the elongated propagation of the surface wave.