From: aufsj@IMAP2.ASU.EDU
Subject: Re: #2. Another EW app for Plasma Mirrors ???
Organization: Arizona State University
Newsgroups: sci.physics.electromag,sci.physics.plasma


RF Trap?

There is a possible corollary use to the "swept plasma mirror"
that I described in my first post. Indeed, it could prove to be of much
greater use (provided it would work, which is what I'm asking).
The plasma mirror will reflect frequencies *below* the "plasma
frequency" while allowing frequencies higher up to pass through. Thus,
raising (or lowering) the "sweep rate" can have a very interesting side
effect besides simply reflecting the RF at a new doppler shifted
frequency. Shouldn't it be able to serve as a "one way" mirror for Rf
energy as well, allowing it to pass one way only----perhaps in effect an
electrically generated radar absorbent material?

Say the plasma frequency is FF. If you know the frequency of a
radar RR that is going to be illuminating you, you should be able to sweep
the plasma mirror towards the emitter at a rate such that:

RR doppler shifted high > FF > RR doppler shifted low

The incoming signal is doppler shifted high---passes through.
But
When the signal hits something, but comes back towards the
mirror, it is now being doppler shifted low---it is reflected, AWAY from
the direction of the original emission.

Sweeping towards
Incoming pulse radar at rate X trapped
|<-----<-----<--| xxx
-------9 GHz -------->>> |<-----<-----<--|(((((8.9 GHz(((((xxx
--------------------->>> |<-----<-----<--|((((( (((((xxx
|<-----<-----<--| xxx
|<-----<-----<--| xxx

Shift to Plasma Freq Reflection meets
9.1 GHz due to 9.0 GHz mirror at 8.9 GHz
Doppler Shift. Filter and reflects.
Passes through.

In other words, the system could function as an RF screen.
Presumably, anything could be hidden behind the screen. As long as the
plasma frequency and the sweep rate are set correctly RF energy is on a
one way trip.
Engineeringwise there could be some leakage. For example, when
the mirror is swept all the way forward it presumably has to be
"eliminated", and even if another mirror is being formed at the back of
the cell there would be RF energy between these two layers that could be
released. Presumably, however, it would only be portion of the energy
not representing the distance between the back of the cell (rearmost mirror
position) and whatever reflective object is 'trapping' the energy. This
is assuming no loss. Even here, you have fouled up anyone trying to find
your range using precision timing (basic radar), the pulse parametrics
may be so different from the released energy as to be unrecognizable, and
at least a portion of the energy is lost.
Even so, consider the following possible set up (I admit I'm
plucking numbers out of the air that just sound reasonable):

A one microsecond pulse hits the mirror as it is sweeping
forward. The plasma frequency is set to the frequency of the radar so the
pulse passes through the mirror easily due to its doppler upshift. 6 inches
behind the mirror is a surface. The pulse hits it and then bounces back
towards the mirror. Because the pulse is now catching up with the mirror
(vice them rushing towards one another) it is below the plasma frequency
and bounces back once again towards the surface. And again, and again, and
again....until the mirror momentarily dissappears (i.e. it has reached the
front of the cell, and is being reformed in the back). Now the remaining
energy leaks/bursts out.
But, if the pulse is 1 microsecond long, and the gap between the
back of the mirror and the reflective surface is one light-nanosecond
long, then every 2 nanoseconds the leading edge of the pulse is bouncing
between the mirror and the reflective surface. In other words, if the
mirror is only "active" for, say, 500 microseconds----then the pulse may
have "bounced" as many as a QUARTER MILLION times before being
re-released (indeed, the leading edge reflects 500 times before the
trailing edge of the pulse even gets past the mirror). Now, imagine that
the "reflective surface" behind the cell was actually a fairly good Radar
Absorbent Material in and of itself. Even with a relatively low
efficiency, it seems that virtually all of the RF energy should have
dissappeared before the plasma mirror is re-formed (well, actually, more
likely converted into heat).
The plasma mirror, then, seems like it could hold RF energy long
enough for it to be converted very efficiently to heat. And, since the
plasma mirror is contained in a low pressure, it seems the cell would be
a poor conductor of heat as well----so an opponent would have problems
seeing an Infrared as well as RF return from the cell. Without even
throwing myself at the numbers, could this be a more efficient way to
transport RF energy for "bulk" purposes----like powering aircraft, or
maybe a little more realistically radios and electronic gear? Could one
use it as an "RF pump" to generate huge energy pulses?

This is interesting stuff to play around with, but as I said I'm
not certain if there is some physics reason to prevent such usage. And
computational electromagnetics is kind of tough even in the simple cases,
Some of these calculations would seem to be pretty challenging. I'd
appreciate any comments/criticisms/feedback. Flames cheerfully ignored :-).

regards,

------------------------------------------------------------------------
Steven j Forsberg at aufsj@imap2.asu.edu Wizard 87-01