Unformatted text preview: Chapter 11 Plasma physics 11.1 Introduction The degree of ionization α of a plasma is deFned by: α = n e n e + n where n e is the electron density and n the density of the neutrals. If a plasma contains also negative charged ions α is not well deFned. The probability that a test particle collides with another is given by dP = n σ dx where σ is the cross section . The collision frequency ν c = 1 / τ c = n σ v . The mean free path is given by λ v = 1 /n σ . The rate coefFcient K is deFned by K = σ v . The number of collisions per unit of time and volume between particles of kind 1 and 2 is given by n 1 n 2 σ v = Kn 1 n 2 . The potential of an electron is given by: V ( r ) = e 4 πε r exp r λ D with λ D = ε kT e T i e 2 ( n e T i + n i T e ) ≈ ε kT e n e e 2 because charge is shielded in a plasma. Here, λ D is the Debye length . ¡or distances < λ D the plasma cannot be assumed to be quasineutral. Deviations of charge neutrality by thermic motion are compensated bycannot be assumed to be quasineutral....
View
Full
Document
This note was uploaded on 01/30/2011 for the course PHYSICS 208 taught by Professor Ye during the Spring '10 term at Blinn College.
 Spring '10
 Ye
 Charge, Plasma Physics

Click to edit the document details