Figure 5. a) Equilibrium potential (V), and b) Currents (e s ^m 2) for a 1 fj,m dust particle of material properties <5m=1.4, Em = 180 eV, x=0.1.
eV, x=0-l to <5m=1.4, Em = 180 eV, x=0-l. For the first set of material properties in quiet Earth plasma conditions, the equilibrium potential was ~ +5 V. However, for the second set of material properties in disturbed Earth plasma conditions, the equilibriuim potential was ~ —3000 V. The charging time was about 10 seconds for a 1 fxm dust particle in quiet Earth plasma conditions, and one-third that time for a 1 fxm dust particle in active Earth plasma conditions. The charging time generally increases with decreasing particle radii.
What happens when we vary the material properties 5m, Em, and x=0-l for a 1 fxm dust particle in the same way in Saturn's magnetosphere, using the same charging processes as we applied for a particle in Earth orbit? Surprisingly, we find very little change in the resulting potentials, charging times, and currents, as seen in Figures 4 and 5. Removing each of the currents, one by one however, does have an effect, in particular the secondary electron emission. If we calculate equipotentials without the secondary electron emission current, then the dust particle potential stays negative throughout the magnetosphere, and doesn't reach positive potentials beyond 8 Rs. On the other hand, removing the photoelectron emission current doesn't alter the equilibrium potentials in a significant way.
The charging time for a 1 ¡1 m dust particle is on the order of a few minutes, while for a 0.01 fxm dust particle, the charging time is on the order of ^,few hours.
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