Talk:Plasma scaling

In the section Cosmic application what does this sentence refer to: The consequence of this is that charged particles moving in very highly magnetised space
plasmas, are somewhat different to what is seen in the laboratory

I think this refers to magnetic fields in space being significantly greater than that which can be reproduced in the laboratory. --Iantresman 10:59, 21 December 2005 (UTC)

In the section Dimensionless parameters in tokamaks what are these parameters: The remaining (dimensional) parameters can be taken to be n, T, B, and R.

I find the subject of this article highly interesting, but it is badly written; I hope someone would improve it to the point of a stand-alone encyclopedia article. --DelftUser 19:34, 14 December 2005 (UTC)

Dimensinos of parameters...

In base dimensions the parameters are:

Particle density n: has dimension 1/length³

The temperature T: has dimension thermodynamic_temperature

The magnetic field B: has dimension mass/(electric_current*time²)

β ~ nTB ^-2

There is no way that β has dimension 1. --DelftUser 19:07, 20 December 2005 (UTC)

The above expression only gives the scaling. In SI units the full expression is

$\beta = \frac{nk_BT}{B^2/2\mu_0}$.

To sort out the dimensions, remember that

$\nabla\times B/\mu_0 = \frac{\partial D}{\partial t} + j$,

so B/μ has dimensions of charge/length/time, and

$m\frac{dv}{dt} = qv\times B$,

so B has dimensions of mass/charge/time (in agreement with your expression). Together this gives for B²/2μ₀ dimensions of mass/length/time². Since k_BT is an energy (mass*length²/time²), nk_BT also has dimensions of mass/length/time². Therefore β is dimensionless. --Art Carlson 08:56, 21 December 2005 (UTC)

Thanks. Is there an article in Wikipedia where β, and the other dimensionless parameters, are defined? If not could you consider adding the definitions to the article. --DelftUser 18:35, 21 December 2005 (UTC)

Plasma (physics)#Dimensionless --Art Carlson 20:42, 21 December 2005 (UTC)