plasma produced at 13 cm downstream from the exit of the accelerator are listed in Table I, which also shows comparisons between the conditions in LEO and the laboratory. According to the similarity law the plasma generated in the space chamber achieves the conditions stated in the preceding section. A solar array of 1.6 m length and the bus voltage of 500 V in LEO can be simulated by a model of 4.4 cm and 3.6 kV in the laboratory because of the same CL parameters. Solar Array Models To confirm the validity of the similarity law the characteristics of total ion current were measured by a simple tungsten plate with one side insulated by a boron-nitride plate of 4.4 cm length square, which is called the ‘baseline' model, and a ‘small' model of 2 cm length square. In order to simulate the 2D/HVexperiment seven configurations were tested, which are shown in Fig. 3 with the baseline model. They are ‘edge', ‘corner', ‘center', ‘diagonal', divided into 4 (‘4div.'), into 9 (‘9div.') and into 36 (‘36div.') models. They consist of a boron-nitride substratum of 4.4 cm length square and tungsten electrodes, which occupy 36% in area of the substratum. Compared with the real HVSA's potential distribution, they were biased uniformly as low as — 3 kV with reference to the ground with a constant voltage power supply of 10 V accuracy. Total ion current collected by the models was monitored by a shunt resistor within 1% accuracy. Drag Measurement The characteristics of the ion drag were measured by the pendulum method. The solar array model was suspended by ceramic rods and tungsten wire from the ceiling of the space chamber and provided with power through a flexible cable. The swing of the pendulum system along the direction of the drag was detected by an optical displacement sensor with an accuracy of a micron. The total error is less than ± 5% and ± 20 /zN. More details are given in Ref. [7], Mass loss of the electrode before and after the drag measurement was also estimated.
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