Observation by Video Camera The experimental simulation using the similarity law enabled us to observe some phenomena by a conventional video camera owing to the dense plasma. The visualization of some phenomena in dilute plasma might be impossible by even a low light TV camera. By a digital image converter the video image was processed into equi-darkness contours. Emissive Probe Potential distribution around the models was measured by an emissive probe mounted on an X-Y table which was driven by a microcomputer. The probe was made of thoriated tungsten wire of 0.2 mm diameter and heated by 5 A current. The probe current was measured according to probe location with constant potential in contradiction to the ordinal way for the emissive probe. When the probe passes through the position having the same potential as that of the probe, the emissive current from the probe changes drastically to near zero. Such a position was defined to correspond to the maximum inclination of the current profile subtracted by the background plasma current. The results have the errors of ±1.3 mm in location and ± 5 V in potential due to finiteness of the probe size, the accuracy of the X-Y table and the potential variation in the probe. 5. Experimental Results Characteristics of Ion Current The ion current dependences on the bias voltage are shown in Fig. 4 at the ram mode in the constant plasma condition. All solar array models increase the ion current with progression of the bias voltage. The ion current of the baseline model is the highest because of the largest electrode. The experiments for the 36div. and the edge models were terminated at — 1 kV and — 2 kV, respectively, owing to occurrence of frequent discharge.
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