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phys documents (dragged) 60 - Chapter 11 Plasma physics...

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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 quasi-neutral. Deviations of charge neutrality by thermic motion are compensated bycannot be assumed to be quasi-neutral....
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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.

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