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Registered Member #1157
Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307
Okay, call me ignorant, but here goes. . .
Why is it that every primary coil I've seen in DRSSTC's are solenoid helical coils, and almost every primary I've seen for SGTC's are flat pancake coils. I see larger, more powerful SGTC coils use the solenoid coil, but then I've also seen them use HUGE flat pancakes.
So I guess I have 2 questions.
1. What is the disadvantage to using solenoid in a SGTC as opposed to a flat primary? 2. Could you make a DRSSTC using the flat primary?
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
1. Overcoupled. Secondary coil saturated with magnetic field leads to racing arcs
2. Heating. The secondary heats up rapidly because the coil is saturated.
3. The variation in coupling changes the ringing of the voltage rise in the secondary coil. Overcoupling ie the secondary being below or too far above a pancake coil causes a change in the coil's damping. I might be able to demonstrate this later, but right now I don't have any pictures of it, sorry.
4. SGTC you want the bottom FEW turns to be coupled to the primary, these are the Current turns. You want to induce a huge RF current into these turns so you get the maximum voltage with the maximum field density in the smallest volume. If you use a solenoid you are spreading out this flux over several hundred turns. But spreading out the flux for a SSTC would be necessary due to heating and the fact that it is continuous wave propagation, whereas the SGTC is momentary.
5. Solenoid is difficult for a SGTC because of dielectric problems. The primary of a 12KV system will ringdown with +12kv and -12kv as the energy is traded between L and C. Top that off with the first couple hundred turns and you have an arcing event. It's very easy to develop very high voltages low in the coil when overcoupled, and the solenoid would lead to racing arcs as well as many pri-sec strikes.
Now if you were using a MOT supply where you have relitavily low supply voltages then you could get away with a solenoid, but when dealing with 10kv or higher you would probably need to go with a flat primary.
There is a 'yes but' in there too. To get around the arcing issue and still use a solenoid, you would configure your system as a Tesla Magnifier. This breaks up the stresses among 3 coils and reduces corona from pri-sec, with the tradeoff of needing a sec-tertiary transmission line which will corona.
I'm sure there's more to it, but others will fill those parts in no doubt.
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Primary Coil: Flat Vs. Solenoid
