Wednesday, October 21, 2009

raw materials

This is where we begin. This is just a quick shot of some of the materials which will (er, might) be used in the fast micro-Marx.

The design is still in flux as I write this. The dimensions of the raw materials I happened to find (at a price I could afford, sort of) constrain parts count depending on the parts. But I have two types of capacitors I could use for the first implementation of this thing.

The next time I take a picture like this, those yellow disks (ceramic capacitors) might be replaced by green cylinders (different ceramic capacitors). The four inch copper pipe will become the coaxial shield (or current return). It also serves as the pressure housing - up to perhaps 200 PSI if I do all my joints right. (use good silver solder and lots of surface area). Unfortunately, terrifically fast rise times are achieved by higher pressures and higher E/d in the gaps than I can manage, due the pressure limit of the pipe. Four inch drawn copper DWV pipe has a rated working pressure of only 257 PSI at 100ºF. Although working pressures from industry standards include safety factors (typically 2X - 2.5X to burst pressure) of their own, I prefer to design on the conservative side rather than on the hairy edge. No unintentional bombs, thank you very much. I've seen what kind of damage energy stored by compressed air can do.

The long sheet to the right is the same ≈.25 phenolic-linen laminate. This will be used to fabricate the support plate onto which the spark gaps, capacitors, and resistors will be mounted. That long, narrow plate will slide into a liner, made from the brown tubing, which is ≈.25 wall, 3.5" ID phenolic-paper laminate. This stuff will hold off 180 kV at least.

One end of the liner will be closed off with a turned plug, permanently epoxied into place, and hopefully degased/debubbled in a vacuum chamber, if it will fit in my bell jar. Must remember to check dimensions of bell jar vs. estimated housing length.

Said plug to be made from the 0.5" material from the big square at lower left.

Not shown is the material - to be determined - which will make up a long narrow insulator passing through the end cap and allowing the dielectric of a cable to enter the housing and plug into the load side of the peaking gap, mounted on the marx panel. Clear as mud?

It'll be clearer once I put up some drawings, after I start to figure things out, and get the drawings to match the real world objects at hand.

The other odds and ends are bushings/spacers for the switch spheres, the spheres themselves (which are likely to get larger) and other miscellanea. There's a box of screws somewhere on my messy bench that belongs with that lot.

Work bench needs cleaning, that's why you're seeing this on a cart.

More as it happens.

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