From: Simon Cast <s341261@student.uq.edu.au>
Newsgroups: sci.physics.electromag,sci.physics.plasma
Subject: Re: #2. Another EW app for Plasma Mirrors ???
Organization: University of Queensland
Approved: plasma@woods.uml.edu


aufsj@IMAP2.ASU.EDU wrote:
>
> 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
>

Several Questions.

1) Could this system be used to control radio noise from electronics
etc. for say a very large radio telescope on the far side of the Moon? A
colloary to this question is could this system be used as an RF filter
to allow band selection?

2) Would it be possible to increase the power and/or the density of this
system to be used as a radiation shield?

3) A follow on to the second question is how is the plasma "contained"?
How long does this containment last?

Thanks.

SImon