Re: FUN: high-speed electrostatic air-threads

[Leigh Palmer <palmer@sfu.ca>]

> On Mon, 15 Jun 1998, Leigh Palmer wrote:
>
> > Sounds like the pinch effect to me.
>
> I considered that, but pinch cannot reverse the expansion of alike charges
> unless they are in a net neutral volume, right?  The pinch effect might
> squeeze the current in a neutral conductor where there are equal - and +
> charges, but for a charged particle stream, e.g. an electron beam, it
> would just slow the outward expansion.  When charged air flows from a
> needle, can the pinch effect squeeze it into a filament, or would the air
> stream act more like an electron beam?

The electrons that leave the tip of the needle don't get very far
on their own, certainly not as far as a millimeter. They interact
with air molecules and do not retain their identities. In a vacuum
things would be quite different. "Field emission" may not be the
best term to characterize phenomena in air at centimeter distances
from the source.

I would expect overall neutrality of the material in the stream. It
is composed of ions of both signs. The electrons (which predominate
the negative ions) are the more mobile, of course. The same thing
happens more dramatically in a lightning bolt. You have a large
current limiting element in your circuit; that's the difference.

Leigh