the average of this potential, the CL parameter for the 2D/HV experiment is calculated to 170. The leak current for the edge model can be estimated as 20 mA in Fig. 15 owing to 0.61 mA/m2 ion current density in LEO. In the same way the ion drag is 24 uN under the assumption that the accommodation coefficient in LEO is the same as in the laboratory. The erosion test revealed the mass loss mechanism is the sputtering. The long-term operation of the solar array of which the operational voltage is higher than the threshold of the sputtering mechanism may degrade the performance of the solar cells. Potential Distribution The ion sheath could be observed as the dark area because ions and atoms are never excited for lack of electron as shown in Fig. 8. The magnitude of the radiation from the excited particles must change drastically in the thermal sheath which is very thin and located between the uniform plasma and the ion space charge sheath. The border of the observed dark area, therefore, can be considered equal to the edge of the ion sheath. As shown in Fig. 11, connection of each ion sheath and covering with entire model were observed. This proves the validity of assumption (3) macroscopically. Figure 12 reveals, however, the complication of the potential distribution in the ion sheath. It is implied that a potential barrier exists in the ion sheath and that the potential on the insulators is higher than the electrodes, though it is not conclusive due to lack of resolution of the emissive probe.
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