Re: magnetic lines like these?

[LUDWIK KOWALSKI <KOWALSKIL@alpha.montclair.edu>]

Subject: Re: magnetic lines like these?
 Referring to:

> > Oh yes, this is important, I think. If protons and electrons have the 
> > same KE (meaning very different v) then traveling in the same direction
> > does not mean that the net B is zero. In a neutral plasma electrons
> > will contribute much more to B than protons. 

Tim Folkerts <Tim.Folkerts@valpo.edu>

> Really?
>
> The CURRENT from the positive and negative charges must be the same
> (or the sun would be acquiring a net charge).  The electrons are moving 
> faster, but are farther apart. Biot-Savart says that B is proportional 
> to I.  Thus it seems that the two contributions must be equal (in 
> magnitude anyway), producing a net B = 0. Or am I missing something?
 
Space densities (of electrons and protons in a neutral plasma) are equal.
Thus the current density, if any, is proportional to the drift velocity.

Naturally, fast electrons will quickly go ahead of slower protons (if KE
distributions are the same). But in a steady state they will catch up with
previously emitted protons, etc.

I have a related question (about plasma "pushed by a pressure difference").
Suppose a mixture of two gases, such as He and Ar in thermal equilibrium,
is inside a long cylindrical tube. A thin alluminum window, at one end of 
the tube, breakes and the mixture is ejected into the surrounding vacuum. 
Each atom gains a non-random velocity component along the axis. Is the 
average non-random velocity component for the He atoms the same as for 
the Ar atoms?
                                        Ludwik Kowalski