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Weird EM question

Started by bitrex March 23, 2015
Suppose I have a hot cathode gas filled tube, argon or xenon or
 something.  The tube is embedded in a solenoid such that the B
 field is orientated parallel to the axis of the cathode and
 anode.  The B field would have a RMS amplitude of say,
 approximately 0.1 Tesla. 

Because of ionization the electron paths under the influence of
 this field probably become chaotic, so we have a good noise
 generator.  

Instead of using a fixed frequency AC to drive the solenoid, what
 happens if the plate output of the gas tube is buggered and
 itself used as the solenoid drive voltage in a positive feedback
 arrangement?  Does the system oscillate at a fixed frequency,
 does the spectrum of noise change, or something else?

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On Mon, 23 Mar 2015 16:19:36 -0400, bitrex wrote:

> Suppose I have a hot cathode gas filled tube, argon or xenon or > something. The tube is embedded in a solenoid such that the B field is > orientated parallel to the axis of the cathode and anode. The B field > would have a RMS amplitude of say, approximately 0.1 Tesla. > > Because of ionization the electron paths under the influence of > this field probably become chaotic, so we have a good noise generator. > > Instead of using a fixed frequency AC to drive the solenoid, what > happens if the plate output of the gas tube is buggered and itself used > as the solenoid drive voltage in a positive feedback arrangement? Does > the system oscillate at a fixed frequency, does the spectrum of noise > change, or something else?
I don't think they'd couple very strongly if at all, at least not magnetically. If you shoved the tube through a toroidal core with windings on it then the tube's anode voltage would couple with the coil. If you arranged things so that the B field was parallel to the tube then you'd have some carrier migration due to the Hall effect (although I couldn't tell you exactly what or how much). But I don't see a magnetic coupling mechanism as stated. There'd be a high probability of parasitic capacitive coupling, but not magnetic. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
"bitrex" <bitrex@de.lete.earthlink.net> wrote in message 
news:5510756b$0$6458$4c5ecfc7@frugalusenet.com...
> Suppose I have a hot cathode gas filled tube, argon or xenon or > something. The tube is embedded in a solenoid such that the B > field is orientated parallel to the axis of the cathode and > anode. The B field would have a RMS amplitude of say, > approximately 0.1 Tesla.
I'd say something like, magnetically biased 6D4, but that's actually transverse, give or take whatever the plate does (being most likely made of nickel).
> Because of ionization the electron paths under the influence of > this field probably become chaotic, so we have a good noise > generator.
Not necessarily. The aggregate flow can be relatively quiet, as tube tech goes. Consider the stability of a 0G3 regulator tube, let alone a buried zener junction. I don't happen to remember why biased arcs are particularly noisy. Something about emphasizing negative resistance, self-amplifying its own noise and all, I would guess. Note that the gas and pressure are extremely important, because some mixes exhibit stable "abnormal glow" discharges, while others have negative incremental resistance. All discharges beyond the 'corona' stage exhibit breakdown of course (allowing such things as capacitive relaxation oscillators, but as for useful negative resistance, I'm not sure).
> Instead of using a fixed frequency AC to drive the solenoid, what > happens if the plate output of the gas tube is buggered and > itself used as the solenoid drive voltage in a positive feedback > arrangement? Does the system oscillate at a fixed frequency, > does the spectrum of noise change, or something else?
I don't see there being a difference; the plate is symmetrical (actually, you didn't say, but I'm assuming a cylinder here), so there's no case for packets of charge to hit it sooner or later, under the rotating influence of the magnetic field. If the plate were channeled (axially), you could get some magnetron action, at least at the lower pressures; maybe there would still be plasma resonances and spooky stuff like that at higher pressure too, but I'm guessing the slow, lumpy, thermalized ions will have very little collective motion and will tend to simply obstruct current flow (as it tends to do, at the... whatever the voltage drop is). Hey, just like politicians... :^) Related reading: Magnetron, Phasitron, 6D4, ..? Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com