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Re: [TCML] Varian/Wallis Multiplier stack

On 4/30/13 11:38 AM, Patrick Reid wrote:
Varian/Wallis Multiplier stack I want use this for a new project I working
on cant find any info on it anyone have any suggestions we are talking
180,000 to 200,000 kvdc at 5ma to the primary coil do the math should be a
hell of a show thanks for any hell you could give me

So you want to drive a TC primary at 100kV?

What were you going to use as the primary capacitor? 5mA @ 100kV is 500W, so power-wise, it's like running a big NST.

YOu're going to do this immersed in oil or SF6 or something? From personal experience, once you start getting much above 30-40kV in air, corona losses (and exciting flashovers) start to be an issue.

If your break rate is, say, 100-150 Hz, you're storing around 5 Joules in the primary C.. so you need 5=C(uF)* 100(kV)^2/2 => C = 1/1000 uF = 1 nF, which isn't too huge. Maxwell/GA makes pulse caps with this kind of voltage rating and capacitance, although more likely, you'd want to series up some smaller, cheaper caps. Maybe a stack of 4 beer bottle/bucket caps?<grin>)

What's your fRes going to be?

YOu're not going to get a significantly higher secondary voltage just because the primary is running at a high voltage. Although if the whole thing is in oil or SF6 or some other useful gas, you might get a Megavolt or more out of it (see Tuve's coil that put out 5MV back in the 30s or 40s).

If the goal is just to get a Megavolt (worthy in and of itself), you might find an impulse transformer to be a better approach. Or if you want clever, some sort of stacked Blumlein pulse former.

A practical detail. Standard voltage multiplier stacks are VERY sensitive to sudden discharge destroying the diodes at the top of the stack. If you short the output, the energy stored in the stack gets dumped through the tippy top diode, usually destroying it. multipliers are usually used for sort of "DC" type loads, and often have some sort of current limiting (series inductor or resistor) to protect them in the event of a flashover.

At 100-200kV, you WILL have flashovers in an experimental rig.. I used a Peltor Tactical hearing protector (like shooters use, about $70) with the gain turned up, you can really hear the evil hiss as the corona starts, but when it goes bang, the headphones shut down to protect your ears and reduce the "startle" response.

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