Experimental Assessments of the Microwave Optical System for the Plasma Wave Measurement by the Fraunhofer Diffraction Method

The method of the Fraunhofer diffraction of an electromagnetic wave, which was recently proposed as a new means to measure the amplitude, the frequency and the wave number of the plasma density fluctuation, is discussed to apply it in the rnicrowave region. The principle of the method is based on the wave-optical description of the influence of afluctuating electron density on the phase of a Gaussian beam passing through a plasma and it is a more general description than the usual active diagnostic methods by an electromagnetic wave in that it includes in itself the usual scattering, schlielen and shadow factors. The necessary conditions of the incident beam and the wave detection for the method were pointed out. Accordingly, the microwave properties and hardwares, especially the beam generation, transmission and measurement, were experimentally examined to establish the measurement techniques and the measurable k_p-limits for this method in the microwave region. The present 70 GHz system was shown to be applicable to detect the plasma waves of k_p＞__～0.3 mm^<-1>