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Wanted: Railgunners in Denver (to work with, or to sell to)

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Gomez

Mon May 13 2013, 10:21PM

Registered Member #2328 Joined: Tue Sept 01 2009, 03:44AM
Location: Denver, Colorado, USA, Sol-3
Posts: 7

Trying to decide whether to continue with my second railgun project or divest.

Background:
I built my first railgun in 1989. It had a 1/4" (yes, 0.25 inches) bore, 5kJ of energy storage in banks of DC filter caps, steel rails, antique mechanical relays for switching... is there any point in continuing? Needless to say, it was suited only for making loud noises. It was not a practical launcher. After learning enough to understand why it had been a dismal failure, I resolved that I wouldn't bother trying again unless:

1) I had enough energy storage at a reasonable voltage, with "enough" and "reasonable" being determined from white papers of groups working in similar scales but with bigger budgets.

2) I had enough lab space with a complete "range" for the gun, chronometer, and projectile trap, and probably including some sound suppression measures as well.

3) I had sufficient instrumentation to measure most of the major circuit parameters and ballistic performance from every shot, including:
â€¢ breach voltage
â€¢ discharge current
â€¢ muzzle voltage
â€¢ muzzle velocity of armature
â€¢ armature erosion
â€¢ armature mass (pre and post)

4) I could think up some practical questions that can be answered with such an experiment (in other words, the basic reason for the project) such as:
â€¢ can a "practical" single-turn (non-augmented) railgun be constructed which meets or exceeds the ballistic performance of a
chemical gun, in approximately the same launcher volume and mass (NOT counting the capacitor energy store) and within
the general operating limits of: 1 meter gun, â‰ˆ20kJ storage, $10K budget?
[ref: "A TECHNICAL ASSESSMENT OF ELECTROMAGNETIC PROPULSION FOR SMALL CALIBER WEAPONS APPLICATIONS, Keith A.
Jamison, Nov. 1990, Naval Postgraduate School -- "Design & Construction of A One Meter Railgun", Fred C. Beach, June 1996,
Naval Postgraduate School]

â€¢ can a closed-field (ie; toroidal) impedance matching transformer be constructed for the above launcher, capable of
transferring 20kJ action, at peak input current on the order of 100 - 300 kA max, and peak output current on the
order of 600kA - 1MA, within a component budget of $1K?
[ref:"High Current Coaxial Pulse Transformer For Railgun Applications", Pappas et al, 1985 and "Design & Construction",
Beach as above]

â€¢ is the performance of matching pulse transformers of this type comparable to sequentially-switched cap banks?

â€¢ does the simplicity of a matching pulse transformer (vs. current pulse shaping by sequential switching) outweigh
its chief disadvantage (difficulty of assembly)?

To my knowledge, no amateur railgunner - and there have been plenty since the web started up - has ever met all of the above criteria. And in my not-so-humble opinion, if you aren't instrumenting your launcher system AND measuring your ballistic performance, then there is very little point in going to the trouble of building the thing in the first place. If all one wishes for is loud bangs and pretty sparks, there are cheaper and easier ways of making same.

I bought my present home (which has space for a shop and lab) ten years ago, and I had been collecting equipment and resources, on a budget, for literally a decade before that. Unfortunately, some of my better, higher-paying jobs got yanked out from under me and I've spent the last five years or so working at an income level which make me doubt I will ever get the second gun lab built. Which leads me to wonder what I am going to do with all this heavy duty pulsed power gear I've been collecting and building.

So now I am looking for people who share my technical goals, who understand the physics and math, who have spare time and money to put toward an expensive project, but who haven't yet been able to gather some of the expensive and exotic resources. I foresee one of three things happening:

1) I meet some more people with the right mind-sets, personalities, and skill sets, who are capable of doing this kind of work professionally (no hack jobs, no duct tape, no hot glue) and we make a real go of it. I have rather high expectations however, and I don't expect this to happen.

2) I find someone who has always wanted to dabble in pulsed power, but has never lucked into the exotic hardware. This would be someone over 25, with a strong background and experience with high voltage equipment, who is willing to sign a legally binding damage waiver and hold-harmless agreement in order to get some free, but dangerous, pulsed power loot.

3) neither of the above happens, and I have it all hauled away for scrap. This looks most likely at the moment.

What sort of gear is involved so far?

I have a large (roughly 2,000 pounds for both cabinets/skids) low-inductance cap bank: 6 x 60uF @ 10kv = 19kJ. The six caps are mounted in a steel cabinet, and they are connected in parallel with a very low inductance parallel-plate current collector arrangement.
The system and the current collectors (I don't call it a transmission line, cuz it AIN'T one) were originally designed to accommodate a single ignitron on each main cap. The ignitrons were dead and were disposed of a long time ago. I also have the original 10kV (@ a few amps, I don't recall) which also includes a large amount of extra components and circuitry required to fire the original ignitrons. I've removed all of the extra trigger components from the cap/switch cabinet. I have not finished re-working the power supply cabinet. Both cabinets are on heavy steel skids which in turn are on big HD casters.

I have a very old (very early) railgap switch built by Tobe Deutschmann in the 1960s or so, which should be capable of switching the entire 3.6C of charge, but it needs some TLC by someone with a clue AND it requires a rather exotic trigger generator to guarantee multichanneling the railgap.

I have most of the more expensive parts for a fast (nS rise time regime) coaxial Marx gen intended to serve as a trigger source for the above, and I've been working on the design in Solidworks, but it isn't built yet. If someone can use them, I'll include the SolidWorks files with those parts.

I have an EG&G trigger generator which needs a new krytron, but it is not fast enough, nor does it have sufficient energy, to work through a dividing network with the above switch.

I have a custom designed and built three-electrode switch designed for experimentation in the pseudospark mode, with field distortion triggering. It is NOT sized for the entire cap bank above, in fact, I had intended to test the switch with ONE of the cap bank caps (ie; 3kJ) at very high peak powers and very short pulse times. I would consider selling it, but I'm inclined to keep it as a conversation piece. It is unlikely to be useful for the railgun in any case.

I have the 2nd gun's pre-accelerator (a technique I'm not completely sold on, but was willing to experiment with) system constructed, but not tested to full pressure yet. (designed to operate at 1,000 PSI with plenty of safety margin, all Sch. 80 steel parts, except some brass or SS components, all rated to at least 3,000 PSI) I have a high pressure (4,000 PSI operating max) bottle regulator to bring Helium down to 1,000 PSI.

I have some materials I intended to use for the gun, including - possibly - the rails. The gun bore was to be 3/4". I'd prefer an even larger bore for this system, but ETP copper isn't cheap.

I do NOT yet have the materials for the gun range, which was to be built on a ten foot length of I-beam, preferably aluminum, but I'd settle for steel if I had to. (ugh) Components to be mounted on the range rail included: injector, gun, blast/flash suppressor, chronometer, and bullet trap. The gun and trap are the longest components, and it's not entirely clear to me that the whole thing can be fit into ten feet of rail. The trap could be made much shorter if preservation of the armature is tossed out, but if we do that, we're not really doing good science or engineering any more. The gun could be made shorter if pre-acceleration is tossed out, but then the power supply MUST have good pulse shaping. In fact, it will probably require good pulse shaping regardless of the injector.

So the question is, are there people in the Denver metro area who are interested in forming a team to do this right? I have machine tools including a mill capable of doing the gun components. What I don't have is the resources to continue pursuing this alone.

If not, is there someone in the area who wants to BUY some of these items? Note: I will not pack or ship this stuff. Some pieces are on the order of 600 to 1,000 pounds EACH. Don't bring a pickup. Bring a commercial flat bed with a fork lift, or bring a commercial box truck with a BIG (deep) lift gate. Bring any friends you have who are the size of linebackers. The pulser is a pure SoB to move.

It would be a shame to dump this stuff, but I'm not making progress, I'm not getting younger, and if I'm not going to be involved, I'd just as soon have the space back to work on other projects. I won't sell the big caps to anybody I haven't met with face to face or who won't sign a damage waiver and hold-harmless. I will not pack up and ship any of it.

As if and when I put other, more portable stuff on eBay, I'll make some separate posts in the For Sale forums.

Gomez

Mon May 20 2013, 04:29PM

Registered Member #2328 Joined: Tue Sept 01 2009, 03:44AM
Location: Denver, Colorado, USA, Sol-3
Posts: 7

After a week, I got only one or two inquiries from people who wanted to support (financially) the project to keep it going, but nobody has volunteered to help do the work, and the total budget isn't there either, so I've decided to divest.

I will be selling (in the For Sale section) the pulse caps and scrapping the cabinets and caster bases, and I will part out the original charging supply and control cabinet, which have a fair number of useful components such as large high current + HV solid state rectifiers, switching devices, pulse transformers, etc.

I have some other lab equipment which ought to interest the physics experimenters here, such as a high vacuum system, HV power supplies, etc. I'll post that stuff in the For Sale board soon.

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