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Spiraform TC streamers & hydrogen/oxygen explosions

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LAN_403

Tue Dec 29 2009, 10:52PM

Registered Member #2372 Joined:
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Posts: 62

I made a drawing that may or may not explain it, depending on how good of a job I did.

If you go through the math you can get a growth rate for the instability which tells you how fast a small perturbation on a current carrying channel will grow. This growth rate will depend on many things and may be hard to find for a channel in air. If these streamers last many microseconds that could be long enough for the instability to have some growth and form a spiral out of what would otherwise be a straight current carrying streamer. If that picture actually explains anythings maybe someone could put it on the wiki so other people can see it too.

Steve Ward

Sat Jan 09 2010, 07:56AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Cool topic! i need to digest it a bit more, but on the topic of long straight sparks, ive been making some with my newest DRSSTC, some pictures of its ridiculous performance can be seen here:

The slow ramping of the applied inverter voltage makes a remarkable difference in spark appearance and length. I must fire the spark starting with the inverter supply voltage near 0, otherwise the sparks become extremely kinked and much shorter like a typical SSTC. I used to believe that resonant frequency would dominate the spark characteristic, but that seems to be just 1 requirement (this coil runs at 360-380khz). Its also worth noting that the topload voltage is probably no more than 100kVAC peak, this is based off of a 2A peak current measured at the base of the secondary coil. I hope to do a more formal write-up on the experiments ive done after i think ive exhausted all of the tests i want to try.

Avalanche

Sat Jan 09 2010, 06:50PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Those are some awesome photos on there

Interesting to note that the rate of rise of the voltage envelope is what appears to cause long sparks to form, that reminded me of the sibniie video on youtube

particularly the end text which I have attached below - which claims that up to 200 meter sparks were generated with just 5.2MV, just by playing around with the rate of rise. This clearly breaks the 'rule of thumb' of 1Kv per mm, so what is going on?

Steve Ward

Sat Jan 09 2010, 07:38PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Not sure if Dex is on this forum, but he posted this to the tcml:

Basically what i gather is that the velocity of ions is slower than electrons, so the ions tend to get left out at the end of the streamer tip as space charge, and on each successive cycle of RF, these ions are pushed out further (this is maybe not a correct understanding, i too need to read that page again).

Though this doesnt address the spiraling, which i note only happens after enough time of driving the streamer (usually more than 2mS or so for my systems).

Dr. Dark Current

Sat Jan 09 2010, 07:57PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Avalanche wrote ...

This clearly breaks the 'rule of thumb' of 1Kv per mm, so what is going on?

With such ultra high voltages, this rule does not apply, I think that's because of air "pre-ionisation"? I think I read somewhere that a lightning strike has something like 100MV, yet it can spark several km.

dex

Sat Jan 09 2010, 08:14PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

Steve Ward wrote ...

Not sure if Dex is on this forum, but he posted this to the tcml:

I registered to 4hv community few weeks ago.Don't know either what exactly causes the spiraling.There are more causes I guess.Perhaps one could be that after the final lenght of spark is reached given the voltage and frequency,the spark can't prolong any more,but as the excitation is still on,it starts to "expand".That process doesn't occur uniformily,and due to it's own magnetic field the spark begins to exhibit "corkscrew" motion.
If you give it say 200 ms powerful enough excitatation,spark would get so thick that spiraling effect is visually completely off. Thick plasma torch effect will replace it.Time scales ,frequencies and peak energies seems to be most important for these things.

Scott Fusare

Sat Jan 09 2010, 10:14PM

Registered Member #531 Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 125

I am sure this has been mentioned before but I'll toss it in again, just in case.

"Spark Discharge" by Bazelyan is the definitive tome on long sparks. Still in print but I see there are used copies available for a fraction of what I paid a decade ago. The author was (is?) a researcher at the Novasibirsk HV facility shown in the YouTube video.

Yes, the correct rise time was all important for achieving the 200m discharge. Rules of thumb such as "30 kv/cm" apply only to cases with a uniform field distribution. That does not hold in our case and most certainly does not hold for the big Marx in Siberia or a thunderhead for that matter. Leader / streamer phenomenon act as an extension of the charge source, hence 200m sparks and many km long lightning bolts.

It's a good read, recommend it highly.

dex

Sun Jan 10 2010, 07:51PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

scott fusare wrote ...

It's a good read, recommend it highly.

Good read certainly.But pretty useless for coiling and completely useless for spiralform streamers discussion here.Maybe that textbook is better suited for Marx generator builders,but these machines are quite different beasts.Sorry to burst your bubble

Scott Fusare

Sun Jan 10 2010, 08:43PM

Registered Member #531 Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 125

dex wrote ...

scott fusare wrote ...

It's a good read, recommend it highly.

My bubble is hardly burst, you'll need a far sharper needle to do that

I never said the book explained the "spiral form" streamers but rather offered it up as a resource to expand upon long spark propagation and why the various rules of thumb do not apply.

I am not trying to draw equivalency between the one off monotonic impulse of a MG and the more complex repetitive, oscillatory TC discharge. That said, the same underlying physics of spark propagation are at work albeit in a more complex form with the TC.

If you've a more appropriate reference that deals specifically with RF sparks and their propagation please share it with the group. I for one am always interested in the subject.

dex

Mon Jan 11 2010, 12:03PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

AFAIK,there are no books on "propagation" of long HF sparks with high repetitive sequence.Just books and references about steady state HF sparks & corona.In the best case you'll find stuff dealing with related problems about radars (usually >100 mhz pulsed HF trails).

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