These are odd little high voltage generators which are in principle, part Blumlein generator (like the nitrogen laser uses) and part induction coil. They are compact and easy to make.
“Continue reading” for more details and photos.
They have two copper strips insulated from each other and rolled up like a rolled capacitor. Apply a few kV at one end of both strips and they will charge up. Short circuit one end with a spark gap and a very fast pulse passes in the Blumlein capacitor strips. This will have a magnetic effect as the current in each copper strip (my brain starts to hurt here) will have an additive effect and like current in a coil will result in magnetic induction in the remaining turns of copper strip
The spiral impulse generator generating a 5 mm spark (perhaps 5 kV) from a 1 mm spark gap. The spark gap is between the two electrodes (which are not connected to each other) and the right upper electrode is the one that continues through to the output electrode strip with the longer spark coming off it. The capacitance between the two strips is 900 pF.
The right photo shows the 2 kV peak input from a small NST limited by a variac. It is half wave rectified and run through a 1 MOhm resistor. My meter reads peak voltage AC or DC as I have designed it.
The circuit of the basic spiral impulse generator with two copper strips with a spark gap between them. The are insulated from each other and rolled up.
This diagram shows the version I am using with extended foil. The larger version I try later has equal foils and works better for a number of reasons.
The 1984 patent that this comes from.
The start of the copper strip windings separated by polyethylene sheet.
The strips of copper foil of 10 x 62 mm obtained as big sheets of 60 cm square from a craft shop. I have soldered two together for the long winding. Hence there are two parallel strips of 4.5 turns and one strip only continues on for another 4.5 turns. It doesn’t seem too efficient but I don’t really understand the set-up enough to know which way to modify it best. I imagine that I could make one with more turns to start.
This is an earlier version that didn’t work other than to light a neon pilot. No real idea why, but later ones with thinner flatter windings worked.
Now here is a better one.
This is a beefier version of the spiral impulse generator .
Specifications:
Output……. bright 1 inch (2.5 cm) sparks (perhaps 30 kV)
Input………. 6 kV peak. (ie 5 times voltage stepup)
Foil………… Equal length copper foils 4.5 cm x 367 cm plus lead in.
Former…… 4.2 x 7cm. Ext diameter 8 cm.
Turns…….. Calculated 20 turns
Spark gap 2 mm
Core……… Ferrrite E cores to fit in 4 cm gap.
Cap………. 45 nF (prev one was 0.9 nF)
Insul………. Polyethylene groundsheet
This new version of the spiral impulse generator seems to have scaled in spark brightness consistent with 50 times the capacitance and also scaled in output spark length 8 mm to 25 mm consistent with the increased turns from 9 to 20. Construction type was similar and dielectric and input voltage were unchanged. The capacitor holds its charge well and if discharged with a chicken stick giving a reasonable “zap”, will give an output spark as well. I suspect that for high repetition rates, the use of a multiple segment gap would prevent power arcing. I also suspect from my experience with TEA nitrogen lasers that the spark gap type and position is critical. The use of a gap with two cylindrical electrodes in continuity with each conductor strip and covering the full width should present the lowest inductance. As it is, it should be able to be driven much harder than just a few pulses per second, but I am not ready to break it yet. It is arcing over already so any better performance would need to be under oil.
Related pages
X-ray transformer 60kV DCTry something else
External links
A commercial one is here
Patent (1979 multiple conductors per layer)
Patent (1996 multiple conductors)
A sort of simple explanation of how they work here
A Blumlein pulse generator using coax cable is here.
Photo Date: April 26, 2008