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Ultra High Voltage Insulator to Metal Bonds Per NEC VP Interview

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Herr Zapp

Tue Nov 17 2009, 11:45PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

jp -

In a quarter-shrinker, inductance IS a concern, since you want to dump all the energy in the cap into the "working coil" as fast as possible. Your gap drawing is essentially identical to Brian's gap, except you don't show any triggering electrode. Inductance of both gaps would be also be essentially identical, with the interconnect wiring being far more critical than the gap itself.

What do you intend to use your trigatron for?

wylie -

Brian's "post mortem" description reminded me of the shadows burned into concrete near Hiroshima ground zero. I can assure you that having a 45 kilo-Joule open-air discharge 10 feet away from you will leave a lasting imperssion!! 5-10kJ coin-shrinking discharges inside a blast chamber are pretty impressive by themselves.

Regards,
Herr Zapp

teravolt

Wed Nov 18 2009, 05:57AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I build polycarbonate pancake switches at work and they will pass many thousands of amps. they are used in large marx systems. I think that polycarbonate is saperior to acrylic and more resistant to solvants. I think they sell for about 1200$

jpsmith123

Wed Nov 18 2009, 03:00PM

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

Herr Zapp wrote ...

jp -

In a quarter-shrinker, inductance IS a concern, since you want to dump all the energy in the cap into the "working coil" as fast as possible.

Herr Zapp,

If this:

is basically his setup, then, obviously, the inductance of his "trigatron" "spark gap" device doesn't matter too much, no?

What generally matters in pulse power applications is that the inductance of the "spark gap" be much smaller than that of the load it's connected to.

wrote ...

Your gap drawing is essentially identical to Brian's gap, except you don't show any triggering electrode.

Well it's similar in the sense that both devices include "gaps", for whatever that's worth. And I didn't show any triggering mechanism because I haven't decided on it yet (and it wouldn't be expected to affect the inductance by much, if anything, anyway).

wrote ...

Inductance of both gaps would be also be essentially identical,

If by "gap" you mean the narrow plasma channel per se, then no, it won't, since his is not pressurized, whereas mine will be (although you can't tell that from the picture I posted), so for a given breakdown voltage, the pressurized gap will be shorter and have less inductance.

wrote ...

with the interconnect wiring being far more critical than the gap itself.

Well the whole design is critical when you're fighting for nanohenries.

You'd be surprised how much of a difference a few seemingly minor differences can make. For example, look at the Pulse Sciences T-670 spark gap. It is specified as having an inductance of 60 nH. Compare that to the R.E. Beverly SG-101M. The SG-101M is specified at <20nH...so there's a 300 percent difference between the two.

In any case, in an application where rise time is critical, and/or the load impedance is low, the inductance is only part of the story. There's also a resistive phase associated with gap breakdown, and that can really slow down di/dt.

In order to minimize the resistive phase and minimize rise time, the gap should operate at as high an electric field as possible...so once again that implies narrow gap spacing and pressurized operation.

wrote ...

What do you intend to use your trigatron for?

To drive some kind of pulsed accelerator, the design of which I'm still working on.

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teravolt wrote ...

I build polycarbonate pancake switches at work and they will pass many thousands of amps. they are used in large marx systems. I think that polycarbonate is saperior to acrylic and more resistant to solvants. I think they sell for about 1200$

Hello Teravolt,

Are your "pancake switches" actually spark gap switches? (I assume they are if they're used in Marx systems). If so I'd really like to know more about them. Do you have any pictures or drawings?

teravolt

Fri Nov 20 2009, 05:24AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hi jpsmith123, the switch is a presurized switch that uses a UV iluminator for trigger. I asked today and they go for 900$. the model I am building today will hold off 100kv in oil or SF6. I will get a link for there spesifications. they have about the same inductance as your powerpoint drawing. how many jouls do you want to pass and what is your application?

jpsmith123

Fri Nov 20 2009, 07:26PM

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

Teravolt I'm not sure yet exactly what I'll be switching, but it'll probably be around 50 kv, and less than 1 kJ; maybe somewhere between 300 to 500 J or so per pulse.

Ultimately I want to accelerate electrons to at least a few Mev, so the spark gap will be driving some kind of "pulse transformer", but as I'm still mulling over various concepts, I can't narrow it down any more than that at the moment.

In any case, I'm aware of only two companies in the U.S. that make spark gaps with plastic bodies - R.E. Beverly, and Titan Pulse Sciences Div. of L-3 Communications (I think they bought out Maxwell's spark gap business). I think R.E. Beverly is in Ohio, and Titan-PSD is in CA somewhere. So maybe you work for Titan-PSD, or is there another manufacturer I don't know about?

Regardless, I'm really curious, what kind of UV source would be used to trigger these spark gaps; i.e., do they use a laser or UV diode or what exactly?

teravolt

Sat Nov 21 2009, 05:10AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I work for titan PSD in San Leandro, the open source link is

the switches are a miplane type of switch that have a uv illuminator to initialize the breakdown of the switch. the pin is connected to say a thyratron through a resistor capacitor network.

what is your buget like. genraly systems are in the hundreds of thousands if not millions. usaly a marx or accellerator will get you into a few million volts

jpsmith123

Thu Feb 18 2010, 02:37PM

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

Hello Teravolt,

I'm wondering, do you have any pictures of the inside of a T-670 spark gap? Or maybe drawings or a "user's manual" or "application notes" or something? The reason I ask is because I'm studying different spark gap designs and I want to try and analyze it to see what the Efield looks like and what kind of creep stress there is and to compare the value of inductance I get with the specified value of approximately 60 nH. Or maybe it's all proprietary and they won't release any of that info?

Unfortunately the published data sheet doesn't go into very much detail on the operating conditions (or anything else for that matter). For example, it's rated as having a max. operating voltage of 100 kv, but it doesn't say if that's in the open air or in SF6 or oil or whatever. Nor does the data sheet specify any max avg. power throughput or any kind of duty cycle limits or derating of any kind.

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