Discharge splitting in QCWDRSSTC

[dru]

Has anyone had any luck with getting their QCW coil to output straight single branched discharges reliably? Right now mine is operating at 317khz, and the discharge keeps branching right away or at about half length. Should I try a higher resonant frequency? My topload is also very small, its a single hard drive disk and with a 3” steel breakout rod positioned 3” above it. I will attach a pic. Thank you
https://drive.google.com/drive/folders/1XOiylS4_rmOnGFGzvwqxlvozTM2rXCon

[Rafft]

with my limited experience:

317KHz is low. try around 400~500KHz. also,  very short ramps ~2mS will also result in splitting. try logarithmic ramp as well.



edit:
ok let me rephrase this. mostly just speculations as qcw is still 'new' and unexplored(?) fully

regarding spliting , MAYBE this depends on what kind of ramp is fed (linear, log, etc) . short ramp-up results on branched arcs compared to longer one.

MAYBE qcw was designed to have a topload. wider(?) major dia would be better . as this would act as shield from the secondary(again, speculation).

edit2
spoke to soon. lol. even on my recent setup, I do get those split arcs. same question as you. HOW/WHY

[johnnyzoo]

Isn't it cool to have branches in those VTTC-style arcs?

Altering the ramp shapes and times sounds like an interesting target for experimenting. An endless number of different ramps can be tried but of course not all of them may be useful.

[dru]

edit:
ok let me rephrase this. mostly just speculations as qcw is still 'new' and unexplored(?) fully

regarding spliting , MAYBE this depends on what kind of ramp is fed (linear, log, etc) . short ramp-up results on branched arcs compared to longer one.

MAYBE qcw was designed to have a topload. wider(?) major dia would be better . as this would act as shield from the secondary(again, speculation).

edit2
spoke to soon. lol. even on my recent setup, I do get those split arcs. same question as you. HOW/WHY

I’ve been working on it a lot and tried a few different things, given QCW coils are still novel devices I tried to come up with unique solutions, not all have worked. The first thing I did was take your advice about the resonant frequency. I had been meaning to wind a better coil for a little while, do I did that and made it’s resonant frequency a little higher. The coil is now wound on a 4 inch diameter tube, 30awg wire for around 800 turns I think. Measured resonance at ~400khz, but this varied quite a bit depending on my setup. I varied the capacitance from .075uf to .3uf, and the best performance I got was with .15uf (2x 3kv .15uf in parallel wired in series with 2 more of the same rating). The next thing I tried was adding a topload, but I wasn’t able to make one that brought any advantage. I don’t have any aluminum spun toroids, just ones I’ve made using home based methods like al duct, hard drive disks, steel disks etc. . The al duct toroids I have all seem too large and heavy, they’re 4in minor 10in major diameter. The only successful addition I’ve made to the coil other than the caps is the breakout rod. It’s 4 inches long with a .3 in diameter, sharpened to a very fine point with a sanding belt with the taper starting 3 inches up. Just to experiment, i put 3 neodymium magnets at the base of this rod to see if it would help directing the field at all. I’m not sure how much a difference that made, but the coil now produces straight, nearly identical vertical discharges at about 20 inches long 110v input. When I go above that at ab 130v input, the discharge splits into 2 or 3 branches about halfway up, though the length is much longer at 35-40in. I’m thinking the resonant frequency must be dropping a lot with discharges that long, so it’s possible resonant frequency is still the culprit here. The final adjustments I made were to cover all exposed connections w elec tape and shield the ground connection. I also added a small strike plate above my driver board just in case the arcs bent, but so far the arcs only travel upwards. I will attach some freeze frame photos of the arcs, a picture of the full circuit, and some videos in an hour or so, the sun just went down so its prime time for filming. Keep me updated on your coil as well. With such powerful branched discharges, I feel like both of our coils are capable of very long straight discharges I’m not sure how yet though.
Thanks!
-Sean

edit: The next thing I’m going to try is changing the primary coil. Right now it is 8 awg insulated 3 turns, I have this super thick 3 awg wire that I will try and wind, it’s very stiff and I can probably only get 1.5 turns with it, so I will have to adjust capacitance down to 10-20 nf.

edit2: sorry wrong direction, I will adjust capacitance to .3-.4uf.

[davekni]

The next thing I tried was adding a topload, but I wasn’t able to make one that brought any advantage.

A topload lowers secondary resonant frequency.  I suspect a topload would help, but only if secondary coil inductance is reduced enough to keep frequency from dropping.