Measurement of Ion Sheath A dark area around the model was observed in the bright ion beam and changed its configuration depending on the array potential, the plasma density and the angle of attack. The edge model with a copper electrode was observed from the direction perpendicular to the ion beam vector at the ram mode as shown in Fig. 8. The experiment using tungsten enabled us to observe the dark area because of dimness on the electrode surface. The dark area enlarged with our increase in the array potential and with a decrease in the plasma density because of a lack of plasma shielding. Figure 9 represents the potential distribution of the edge model measured by the emissive probe at the same condition as Fig. 8 except for the electrode material. From the emissive probe data were identified the positions corresponding —40 V with respect to the plasma potential in the cross-section at 50% span. It is noted that the ion beam energy was 40 eV at this experimental condition. Each cross bar represents the spatial error. The border of the plasma sheath in Fig. 8 agrees with the contour of the measured position in Fig. 9. Figures 10 and 11 show the spacial potential distributions of the 9div. model at the ram and the wake modes, respectively. At the ram mode the —40 V contour of each ion sheath formed on each electrode is separated by the insulators located between the electrodes. On the other hand, at the wake mode the — 40 V contour is connected with each other so that the entire solar array model seems to be covered with a single ion sheath. The — 400 V contours are still independent of each other. The more detailed distribution at the wake mode was shown in Fig. 12. With restriction of the emissive
RkJQdWJsaXNoZXIy MTU5NjU0Mg==