Plasma parameter: Difference between revisions

Revision as of 15:43, 25 January 2012

Revision as of 14:53, 12 October 2012

Line 1:

The ''plasma parameter'' is a dimensionless number, denoted by capital Lambda, Λ. The plasma parameter is usually interpreted to be the argument of the Coulomb logarithm, which is the ratio of the maximum impact parameter to the classical distance of closest approach in [[Coulomb_collisionCoulomb collision|Coulomb scattering]]. In this case, the plasma parameter is given by<ref>Chen, F.F., Introduction to Plasma Physics and Controlled Fusion, (Springer, New York, 2006)</ref>:

:<math> \Lambda = 4\pi n \lambda_D^3 </math>

Line 5:

where

:''n'' is the number density of electrons,

:λ_D is the [[Debye length]].

This expression is typically valid for a plasma in which ion thermal velocities are much less than electron thermal velocities. A detailed discussion of the Coulomb logarithm is available in the ''NRL Plasma Formulary'', pages 34-3534–35.

Note that the word parameter is usually used in plasma physics to refer to bulk plasma properties in general: see [[plasma parameters]].

Line 35:

One of the criteria which determine whether a collection of charged particles can rigorously be termed an [[ideal plasma]] is that Λ>>1.

When this is the case, collective electrostatic interactions dominate over binary collisions, and the plasma particles can be treated as if they only interact with a smooth background field, rather than through pairwise interactions (collisions) .<ref>J.D. Callen, University of Wisconsin-Madison, Draft Material for Fundamentals of Plasma Physics book: Collective Plasma Phenomena [http://homepages.cae.wisc.edu/~callen/chap1.pdf PDF]</ref>. The [[equation of state]] of each species in an ideal plasma is that of an [[ideal gas]].

== Plasma properties and Λ ==

Line 55:

==External links==

* [http://wwwppd.nrl.navy.mil/nrlformulary/NRL_FORMULARY_07.pdf NRL Plasma Formulary 2007 ed.]

<!-- Categories -->