Talk:Debye length

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Hannes Alfven would role over in his grave if he saw that the solar core had no magnetic field.  —Preceding unsigned comment added by 75.157.177.51 (talk) 19:05, 22 February 2008 (UTC)

message: Maybe the formula for the Debye length should be modified to take into account negative ions? Ga2re2t 17:02, 28 October 2007 (UTC)
thread_title:  Electronegative Plasmas 

message: The formula for a plasma is given as
: \lambda_D = \sqrt{\frac{\varepsilon_0 k/q_e^2}{n_e/T_e+\sum_{ij} j^2n_{ij}/T_i}}
and then it is stated 
:The ion term is often dropped, giving
:: \lambda_D = \sqrt{\frac{\varepsilon_0 k T_e}{n_e q_e^2}}
:although this is only valid when the ions are much colder than the electrons.
Mathematically, assuming quasineutrality and reasonable charge states, taking the limit T_i/T_e\rightarrow0 doesn't make the ion term disappear, it makes it dominate. That makes some sense physically, since cold ions (like any cold charged particles) will cluster more compactly around foreign charges, shielding them before warm charged particles have a chance to notice them. What is wrong with this argument, and how can the article be rephrased to make mathematical and physical sense? --Art Carlson (talk) 09:52, 11 January 2008 (UTC)
replies: text:  \lambda_D = \sqrt{\frac{\varepsilon_0 k T_e}{n_e q_e^2 (1 + T_e/T_i)}}
The mentioned simplification could only be valid if the electrons (not ions) were much colder. CharlieM, 10 May 2008  —Preceding unsigned comment added by 81.61.248.109 (talk) 19:22, 10 May 2008 (UTC)
thread_title:  Cold ions 

message: This page about the "Debye length" makes incorrect statements:
To name a few:
1) " ... where, as a mathematical convenience for purposes of illustration, the charge has been arranged to vanish when the potential is zero"
In fact this can never be done and though there is some leeway in choosing the potential (gauge invariance) nothing like that will add a 1 to 
 http://upload.wikimedia.org/math/0/5/c/05cc7eee4bbdbb80aea1034e82965fb4.png
The "1" is there to represent the opposite charge background and is a physical necessity rather then a mathematical convenience.
Which leads to:
2) "It is assumed that the potential has the correct polarity to raise the energy of the charges screening the potential"
No. The polarity of the field comes out of the equations with no such imposition.
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Summary: It was very nice of someone to try and explain the Debye length! They, along with everyone else who would like to correctly understand its derivation (with its limitations, e.g., decoupling the background charges from the field(!)) should at the very least open up J. D. Jackson's 2nd Edition "Classical Electrodynamics" (AKA as "The Bible" among some) to page 495 and enjoy. (and then write back a proper introduction)
Have a good day and keep up adding/correcting wikipedia.  —Preceding unsigned comment added by 65.26.183.175 (talk) 21:36, 13 August 2009 (UTC)
thread_title:  CAUTION! 

message: Are you sure Debye length is \lambda_D =
\left(\frac{\varepsilon \, k_B T}{\sum_{j = 1}^N n_j^0 \, q_j^2}\right)^{1/2}
Instead of 
\lambda_D =
\left(\sum_{j = 1}^N \frac{\varepsilon \, k_B T_j}{n_j^0 \, q_j^2}\right)^{1/2} ?  Heitorpb (talk) 16:53, 17 October 2015 (UTC)
thread_title:  Debye Length Formula