Re: Plasma

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:
 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
><jimlux-at-earthlink-dot-net>

> > > << A plasma nead not be hot,

> > It does.

> > > it only must be ionized.

> > Ionized is another way of saying 'hot'.

> Nope...

	cf above.
	(The usage is more rigorous, tho uncommon.)
	(we can get wound up in semantics on this one...)

> you can ionize a gas without doing it thermally, and without having
> the atoms moving fast (which is what temperature is all about, really...)

	Temperature is a measure of particle speed.  Particles can
	be atoms OR ELECTRONS.

	If the electrons are moving fast they are hot.  So is whatever
	(if anything) they are part of.  (hint:  THAT'S why plasmas
	are so reactive: they are HOT.)

	Now:
	in many cases, the plasma is so 'thin' that it does not appear
	to any but the most specific instruments.  It is, however, hot.

> Consider the following.  I have a volume of gas.. I blast an intense
> xray source at it.. temperature remains the same,

	If energy goes into it, and stays there, the temperature rises.

> but the electrons are stripped off the atoms, forming an ionized gas.

	Now moving fast (free of atoms, recall) THEY are hot...
 
> Consider this... I have a chamber pumped down to, say, 1 torr...
> I add a small amount of RF power.. the gas ionizes.. Is it hot?

	yes.
	In the physics sense.
	The temperature rises, but since the gas (now plasma...) is
	so thin, measuring that is tricky.  Can be done.  Put another
	way: the temperatures are high, but the AMOUNT of heat
	remains low.

> How about an ion gun? generating ions at, say, 0.01 eV...  at
> 1 eV=11000K, that's 110K... (although I'm not sure that the
> 1eV=11000K doesn't really refer to a Maxwellian or thermalized
> distribution..)

	cf above.

> I think the upshot is that in air at usual temperatures and pressures...
> heat and ionization go together.  But, there are enough situations where
> temperature, heat, and ionization might be decoupled, particularly at low
> pressures.

	cf above.

	best
	dwp