Wednesday, October 14, 2009

Brain has returned to being obsessed with the "micro-Marx".

There's a perfect piece of copper pipe on eBay for this project. I'm hoping it won't sell and that I can contact the seller next month. There's not much call for that sort of thing these days. Most sensible and non-wealthy people use PVC for their DWV pipe. So I have high hopes there.

When I am sitting at the corner of our big surface plate at work, measuring pulley after endless pulley, I think of nothing else. I was just doing that, and will return to doing it shortly, but I had to get this crap written down before I forgot all of it again.

When I can't actually do any real work (ie; in my shop) toward a project, such as last night, I make pictures in my head like SolidWorks and try out ideas of how things might fit together, how a joint ought to work for technical reasons versus the limitations of my fabrication capabilities (thankfully few, these days, toot-toot!)

Out of all this head-crunching have come many more unanswered questions. I put them here as much for my own convenience to refer to later (and I'd better pull this onto my home computer, as I don't trust online services to continue to exist) as for any education or entertainment you all might derive from it:

1. Now that I'm no longer using (suboptimal) PVC pipe for the liner, how will the Marx panel be mounted / held rigid within the phenolic liner?

2. Should the peaking gap be included within the Marx device proper, or be an optional external device which can be attached to the output or not? There are advantages and disadvantages to both designs.

3. What will the connection between the Marx panel and the output insulator (or the peaking gap as may be) look like?

4. If the peaking gap is internal, then the output will be directly into RG8 or optionally, a short insulated conductor that goes directly to the trigger plane of the switch. In that event, what will the Doran-style HV receptacle for that cable look like?

5. Is there room inside the liner and on the Marx panel for the trigger generator? If yes (and I doubt it) it would mean I could (probably) design it to charge itself off the stage charge voltage.

6. Would it be better to add more stages for other possible applications? If I do that, I will almost certainly have to move the trigger generator outside the housing. I probably should anyway. It's not very big, although I would have to add some SHV connectors, which are expensive, and there'd be this dangling dongle on the outside, which offends my delicate sensibilities. I really ought to try to obtain another TM-11 trigger generator or similar device.

7. How wide an operating range is practical for these compact Marx pulsers? More trigger voltage for the big switch is better... only up to a point. 10X the operating voltage seems to be a typical maximum. If I add stages to the Marx, I don't want to find myself incapable of operating below some maximum trigger voltage (probably 100kV). The operating (or stage) voltage is determined by Marx operating pressure (which is adjustable) and spark gap distances (which are not).

#8: Part of the design is to use pure(ish) dry nitrogen as the switch gas. Using N2 vs. air should increase the UV output of each switch. _IF_ I have enough stage energy to generate significant UV from each gap at all, using N2 will make it better. High UV emission from gaps (to illuminate adjacent gaps) is extremely desirable for fast erection time.

To that end, where shall I obtain the N2? Should I just buy a tank of some blowing my budget into low earth orbit, or is there an easy way to remove most of the oxygen from a dry air stream? The latter would be convenient, since I recently purchased an automatically regenerating commercial air drier-compressor combo for next to nothing.

I think the answer to this one will be found via the Lasers List.

In short, it is easy to do these things informally, if all you want is big sparks. It is non-trivial to do these things very well. I wish I had a bunch of physics and math and a EE (or more preferably a PhD) under my belt. I might be able to do this sort of thing on a consulting basis. You should know that there's a metric butt-load of DoD money to be made in the pulsed power field.

I need to figure out how to turn ($THING_I_LOVE_TO_DO) into dollars.

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