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Spiral impulse generator = rolled cap Blumlein induction coil!

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LAN_403

Tesladownunder

Sun Apr 20 2008, 07:52AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

If you have 50m of coax and are happy to setup some spark gaps then you can make a tripler but this is capable of greater multiplication of voltage and is much more compact.

Somehow, I dont see solid state being that good at 100 nanosecond switching at 10kV. Spark gaps are free, Klystrons are available but acres of high voltage fast silicon is not how I would go. Not today at least...

I am making a larger one for experiments with about 10 times the capacitance (10nF). Might not get it done tonight though.

TDU

flannelhead

Sun Apr 20 2008, 09:05AM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Does it have to be copper or could I try with aluminium foil?

Proud Mary

Sun Apr 20 2008, 09:40AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

spark wrote ...

Does it have to be copper or could I try with aluminium foil?

Aluminium will work fine.

Bored Chemist

Sun Apr 20 2008, 09:41AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

I have dismantled a commercial one of these from a portable xray unit (dead, alas). It had a ferrite core.
You might want to add a core of some sort and see what happens.

jpsmith123

Sun Apr 20 2008, 12:04PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Mates wrote ...

I have few ideas regarding this thread...

What about to try coax cable istead of the rolled-insutated stripes...Would it work?

And it would be interesting to try solidstate based "spark gap" because as understand this concept it has no real frequency limit (maybe such device could be used for plasma speakers ???)

Strictly speaking, I think you can't make a "spiral" generator from coax...but you can make a "stacked blumlein".

Proud Mary

Sun Apr 20 2008, 02:44PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

This design using flat ribbon cable has to be the easiest and simplest spiral generator I've found yet:

"Stripline transformer adapted for inexpensive construction"

United States Patent 4717834

Mates

Sun Apr 20 2008, 08:53PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

How important is to make one of the stripes longer? Does it affect the pulse duration and/or the final voltage?

Tesladownunder

Sun Apr 20 2008, 11:56PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Harry wrote ...

This design using flat ribbon cable has to be the easiest and simplest spiral generator I've found yet:
"Stripline transformer adapted for inexpensive construction"

Sounds pretty easy. 12 feet of 8 core ribbon and a aluminium foil strip around a 1.9 inch former with a mercury wetted relay switching 160 V to get 2500 V peak at 20ns.
I wonder if the ribbon is not just convenient but is also acting like Litz wire and hence possibly more efficient.
It should handle more voltage too, since the voltage is evenly spaced between turns.

I have about 20m or more of 3m wide poly of the same sort I used for the small one. Alfoil is cheap so a really big generator run at higher voltages might be feasible. The problem with alfoil is the termination at the spark gap end which needs to be low inductance and low resistance. I've not found aluminum solders to be that effective. Fortunately I have a few square meters of copper foil which solders nicely.

TDU

Proud Mary

Mon Apr 21 2008, 12:37AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

From what I've understood so far, the maximum output voltage is given by Vout = 2nVin, where n is the number of turns.

The total charge is that which can be stored on the two strips in straightforward capacitor mode, so the more surface area the strips have, the greater the output pulse power. I'm not clear if the flat ribbon shorted across both ends can act as though it were a single capacitive electrode in relation to the ground plane or not.

I agree about the problem of making reliable low Z connections to aluminium foil, which I would prefer to use rather than my small stock of self-adhesive copper foil and sheet.

As a first attempt, I thought of making a sandwich of 75mm aluminium adhesive tape and 100mm insulating tape with one sticky side down, but don't want to commit money to it till I have a better understanding of how thick the insulation needs to be, because there'll be no unpicking it all if the dielectric breaks down.

As I understand it, the insulation needs to increase in proportion with the number of turns, which can result in high voltage Vector Inversion Generators becoming physically large.

Proud Mary

Mon Apr 21 2008, 11:26AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I see that NASA has a page on Vector Inversion Generators in its commercial successes section:

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