physics 122 Lecture 02 October 1st 2013_final

1 chapter 2 single parcle moon introducon as we

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Unformatted text preview: bye shielding would not be a statistically valid concept. We can compute the number of particles in a “Debye sphere”, ND, as 4 N D = n π λ D3 3 In addition to λ D << L, “collective behavior” requires N D >>1. Criteria for Plasmas We have given two conditions that an ionized gas must satisfy to be called a plasma. A third condition has to do with collisions. The weakly ionized gas in a jet exhaust, for example, does not qualify as a plasma because the charged particles collide so f requently with neutral atoms that their motion is controlled by ordinary hydrodynamic forces. If ω is the frequency of typical plasma oscillations and τ is the mean time between collisions with neutral atoms, we require ωτ > 1 for the gas to behave like plasma rather than a neutral gas. The three conditions that a plasma must then satisfy are 1. λ D << L 2. ND >>> 1 3. ωτ > 1 Chapter 2 Single Par;cle mo;on Introduc;on As we know when par;cles move [charges] they generate local concentra;ons of +ve and- ve charges giving rise to E fields. Mo;on of charge...
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This document was uploaded on 01/17/2014.

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