From: Arthur Carlson TOK <carlson@ipp-garching.mpg.de>
Newsgroups: sci.physics.plasma
Subject: Re: Plasma questions
Organization: Rechenzentrum der Max-Planck-Gesellschaft in Garching


fodder@ix.netcom.com (Mike Greenberg) writes:

> 1)What part of a flame is plasma? Does it have a magnetic field?

Roughly speaking, a gas which is hot enough to glow is hot enough to
be significantly ionized. I wouldn't expect a magnetic field
appreciably stronger than the ambient.

> 2)Does the earth's magnetic field affect fire or plasma?

I would expect the collision frequency to be much larger than the
gyrofrequency, so, No.

> 3)Since electric current is random in a plasm, there should be no
> field. But can you make an diode plasma? Or what about lighting a
> diode on fire? If you ignite an LED, will it light?

I can't make any sense out of this question. There can certainly be
a net current in a plasma. A plasma surface interface acts very much
like a diode.

> 4)What is the resistance of plasma when conducting electricity, and
> what factors influence it?

The conductivity in ohm-m of a fully ionized plasma (which a flame is
not) is

5.2e-5 * Z * ln lambda / T_e^(3/2)

where Z is the charge of the ions, ln lambda, known as the Coulomb
logarithm, is a weak function of density and temperature usually equal
to 10 or 15, and T_e is the electron temperature expressed in electron
volts (eV). Thus a plasma is a poorer conductor than copper unless it
is hotter than about 1 keV (10 000 000 deg).

--
To study, to finish, to publish. -- Benjamin Franklin

Dr. Arthur Carlson
Max Planck Institute for Plasma Physics
Garching, Germany
carlson@ipp-garching.mpg.de
http://www.rzg.mpg.de/~awc/home.html

As usual, if I am caught or killed, the Institute
will disavow any knowledge of my actions.