In the noninteracting limit and with the following assumptions: (1) the sheath does not spread radially from the conductor; (2) the ions are cold; (3) all segments are identical; (4) the accommodation coefficients for the conductor and dielectric are the same; it is possible to evaluate the drag and lift coefficients analytically. The drag coefficient is then: and the dimensionless conductor area is ac = nsJinterconnect/Jarray. These analytic estimates will give an underestimate of the drag and lift in the noninteracting limit since thermal effects and sheath spreading are ignored. Use of a Particle in Cell Code to Simulate Ion Drag In order to obtain a more realistic estimate of the drag and lift coefficients in the noninteracting limit a 2-dimensional PIC code was used to simulate the detailed physics over the surface of an array segment composed of a conductor surrounded by a dielectric. The PIC code was developed from PDW1[4]. PDW1 is one-dimensional in real space and three-dimensional in velocity space. The geometry of the PIC code is shown in Fig. 2. On the right side of the system is a conductor with a dielectric on either side. This enables the surface charging to be modelled. The boundary condition on the potential over the dielectric plates is E-n = a/e0 where o is the charge on the plate. The potential over the conductor is taken to be the biased potential. The boundary condition over the rest of the boundary is taken to be 0=0 or S0/Sn=O. The computer code allows injection of electrons and ions at the boundaries at an arbitrary angle with respect to the plate. The ion to electron mass ratio was taken as 100, and both particles were injected from the left hand side, top and bottom boundary with Maxwellian distributions consisting of a drift velocity and a thermal velocity. They are given by ©eiectr„n thermal! ®drift: ©ionthermal= 1:0.7:0.07. Secondary electron emission from the dielectric was allowed. The system was taken to be a square of dimension 32 by 32 units or sometimes a rectangle of 32 by 48 units. The spatial grid was also chosen as 32 by 32. The conductor was taken to have a length of 3 units and to have a dielectric on each side of 13 units. The simulations were always started with 4500 electrons and 4500 ions. This choice of particle density gives the grid size as one Debye length.
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