physics 122 Lecture 02 October 1st 2013_final

1 chapter 2 single parcle moon introducon as we

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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...
View Full Document

Ask a homework question - tutors are online