ITN: Primordial Deep Space Magnetic Fields

[bojan]

Originally Posted by CraigS

I may have misjudged the Relaxation Oscillator thingy also.

Alex forwarded us a paper which contained a model of transmission lines.

What's that got to do with a Relaxation Oscillator ? I asked.

Apparently what they're saying is that a pulse entered into that system bounces up and down the transmission line (like what caused power blackouts in the Northern US). The pulse continues bouncing back and forth between impedance boundaries simulated by the combination of modelled elements in the transmission circuit model. This then, starts to emulate the behaviour of a Relaxation Oscillator. Mind you, each time the pulse rebounds, it loses energy and eventually dies out due to losses in the transmission line media.

I'll have to re-read the Peratt/Healy paper again on this one.

This post should also be on our 'Primordial Magnetic Fields' thread. I might copy it over there, for the record (& for Bojan to shoot me down on this .. oh you can, too http://www.iceinspace.com.au/forum/....es/happy19.gif )

.. I'm not saying that any of this makes sense, yet .. I'm just seeing that there may be a lot of miscommunication going on as the Electrical speak comes together with AstroPhysics .. not of our making .. it's up to the PC authors to have explained all this much more clearly .. and they haven't.

http://www.iceinspace.com.au/forum/....es/happy19.gif

Cheers

You didn't misjudge anything.

For an 'oscillator' to be called an oscillator, you have to have amplifier and feedback.
The feedback must be of such a nature, that the 'open loop gain' is bigger than 1 (one), and the phase is close to 0° (or 360°)
If you don't have those elements. you don't have an oscillator.
Now, gain means, there must be an input of power from somewhere (even internal power source will do) to sustain oscillations, otherwise, as you pointed out, they will stop after couple od periods, sometimes even sooner (as in case of relaxation oscillator .. which, BTW, doesn't have frequency selective circuit, like transmission line.. it has TWO amplifiers, for phase shift of 180° each).
ANY model of the pulsar must firstly explain the unusual frequency stability - as we (RF electronics engineers) know, oscillators are very unstable circuits in terms of frequency, especially when Q factor of the circuit goes low (high losses in the circuit... which is radiation of energy in any form from the system).

As I said before, and I am repeating now, in Peratt's there is NOTHING that looks like an oscillator.
It is more like very crude and simplified equivalent circuit that tries to model currents in ionised environment over large distances (up to couple of hundreds of thousands kilometres.. to explain relatively low pulse repetition rate - milliseconds to seconds).
The only thing that looks like active element is that variable resistor... but there is no feedback path.. and energy source is not determined.
If I were the teacher in high school, noone with paper like this would pass the exam as far as I am concerned.

[CraigS]

Hmm

This is tricky .. not what Bojan has said (totally agree with him), but the mish mash of information before us.

There are two circuit diagrams in two separate papers.

The first one (Radiation Properties of Pulsar Magnetospheres, 1995) shows a transmission line model (Fig #6). This is the crude model used by Healy & Peratt to 'emulate' the signals emitted by a pulsar.

The second circuit diagram (called Figure #7), in the 'Advances' paper, 1998 (I believe), shows a generic model of a space plasma problem .. in this case, the flow of Birkeland currents in the Earth's magnetosphere/ionosphere. I can see a variable resistor in this one .. and a big EMF (potential difference source) ... 10e4 to 10e5 volts.

Neither is what you'd call a relaxation oscillator (for reasons Bojan has made clear).

Scott's lecture on Youtube at the 8:30 mark refers to paper #1 (1995) above. In his lecture he mentions the reflected wave on a transmission line and then talks about how easy it is to recreate a relaxation oscillator in the lab. He highly recommends the 1995 paper. He says the paper provides simulations of "17 of the known properties of Pulsars". He flips between using the term "Relaxation Oscillator", and the transmission line model, with pulses injected into it.

The implication being that this is THE Relaxation Oscillator model.
If it is THE Relaxtion Model for Pulsars, then it does not demonstrate Relaxation Model characteristics, so I still don't understand the analogy, in modelling terms.

Just wanting to get this clear ..in spite of the poor written and lecture communications by Peratt, Healy and Scott.

Cheers & Rgds.
PS: In Scott's lecture, his slides say: "Stable frequencies in trapped-ion clocks are equal to the observed outputs from pulsars" .. and .. "Plasma transmission lines from one location on a star to another - or between members of a closely spaced binary pair can easily produce these oscillations".

[bojan]

Originally Posted by CraigS

"Plasma transmission lines from one location on a star to another - or between members of a closely spaced binary pair can easily produce these oscillations".

I would like to see Alex's explanation of that "easy".

[CraigS]

Originally Posted by bojan

I would like to see Alex's explanation of that "easy".

Well .. the language in the slide sets that scene ..

closely spaced binary pair can easily produce these oscillations

Cheers

[bojan]

Which is pure speculation.

[CraigS]

Until we see more on this .. 'Yes'.

Cheers

[Jarvamundo (Alex)]

keep it in the peratt thread?

[CraigS]

Nice try … & clever, Alex ..

The other thread doesn't contain the last six posts of this thread .. which serve to weaken the Relaxation Oscillator hypothesis/model down to speculation.

This post is just to denote that .. for continuity's sake.

I could make the same post on the other thread .. but I've lost interest in such games. If it becomes necessary, I'll reference back to this post.

Cheers