Win's next 10kV project, a 1us ramp

On 7 Jan 2006 05:50:21 -0800, Winfield Hill wrote in Msg.

What is it you're measuring?

robert

Its not a "sure recipe" for breakdown but certainly a good start on getting breakdown. COAX that is able to handle 10KV is going to be bulky, perhaps too bulky to handle.

You may be able to get good enough leakage with ordinary methods. One thing worth looking at is enclosing the transformer in copper. If you keep the lines of force from getting away, you generally reduce the leakage inductance.

There seems to be a fundamental problem here: What we gained in lower leakage inductance, must be payed for with extra capacitance. So the answer would be to have a floating driver on each section of primary, be it coax or conventional. Complicated but possible. /Sven Wilhelmsson

Copper around toroids??????

What, you didn't enjoy the two, three days of discussion?

And you, of all people, are asking for advice from this pack of weinerheads? ;-P

Good Luck! Rich

Yep, good fun, almost understood some of it. This Vbe stuff, has anyone documented it, or can I download the internet onto a floppy or two?

martin

No, it takes three DVDs. ;-)

Hmmm, subtract the p*rn, the copyrighted stuff that's illegal anyhow, the political BS, manuals for stuff nobody owns anymore, and you're getting close...

Mark L. Fergerson

I saw a powdered iron pot core a few years back that was about 12" OD, perhaps 10" high, and far too heavy to hold in one hand. Alas I forget who made them.

Cheers Terry

Well, if you include that stuff, you'll need a few more DVDs. ;-)

You're probably thinking of something made by PerkinElmer,

Please check me on this but there is supposed to be something like a field emission switch, speed like a fast SCR, power handling like a thyratron. It would switch kilovolts in 10 to 20 nanoseconds and handle 10's to 100's of Amperes. decent durability too.

I looked through the catalog but those things do not behave like what i read about. One specific advantage was faster switching that the spark gap things.

I haven't found any of them, but 5D21 tubes are available from WW-II days. Thanks for the suggestion, they look promising.

Looking at the curves, I'm amazed they can go that high, is that with a positive grid and a high plate voltage?

We need a -3kV to -13kV voltage ramp, but a good way to get that is a constant sink current into the node capacitance. For example, if the capacitance is 100pF we need 1A for 1us. I checked the 4CX35000. Whoa! It's huge, 50# and 17" high by 10" dia, and needs 300W in the filament, sheesh!

We're still evaluating the cycle time.

The more i read and think about this the more it sounds like a sweep circuit with a high voltage flyback transformer for the output ramp.

i have been digging around and they can handle about 20 to 25 mA continuous and about 200 mA peak 1% duty cycle and gave up on them as a poor target. But that set me off onto power tetrodes from Eimac. Easy to get serious overkill but they are available and you could probably drive them grounded grid from a single 1kV 3A FET. Assuming relatively clean triangular pulses the power dissipation in the FET won't be too bad. And a 4CX35000 can certainly do its part; 20 kV anode / plate, 6A, PD 35000W (used in VHF transmitters to 110 MHz and 195 kW). Last problem is that output mode is still current rather than voltage, and i don't know how important getting a voltage ramp is. I don't recall what the intended repetition rate is but IIRC it as about 1 PPS? This setup could go 1000 times faster (save test time?)

Yes, harder... I can easily handle a design for 50:1 spread with low-droop requirements, for an "ordinary" transformer, but for one insulated for 10kV, I'm not so confidant.

Maybe, maybe not. What you get that's linear on a typical HOT is the charging-current ramp, and not necessarily the transformer's output-voltage, which doesn't have an ramp as a goal. Still, a discharging flyback transformer could exhibit a constant output current, making a linear ramp into a capacitor... So, I'm still thinking about it.