In an electrically isolated plasma the ions and electrons cannot diffuse independently of each other since this would violate neutrality. Any small deviation from neutrality is evidenced by the presence of an electric field. This field acts to inhibit any further charge separation. As a result of the “lagging” particles, the motion of those particles that move ahead is retarded. The situation is similar to that which occurs on guided tours, in which the entire group must observe the pace of the slowest member. Of course, the trailing particles also have a tendency to be pulled to the front, but to a lesser extent than the tendency for leading particles to be held back. In the simplest case, if the diffusion coefficient for particles of one sign is very much larger than for particles of the opposite sign, the total diffusion coefficient will only be half as large as the largest individual coefficient. This combined diffusion of oppositely charged particles is called ambipolar diffusion.
KeywordsMagnetic Field Polar Diffusion capaCitor Bank Longitudinal magnetiC Field Axial Magnetic Field
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