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Flux concentrator.
Posted by Ben on 4/23/2004, 3:55 am Is there some reason why not?
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Re: Flux concentrator.
Posted by Bert Hickman on 4/23/2004, 9:23 am, in reply to "Flux concentrator." That's an excellent question, and a rather uncommon one. Are you in the field of electromagnetics or particle physics? I have considered using a flux concentrator but I haven't actually tried it. As you know, a flux concentrator could be made from a cylindrical piece of copper or aluminum with a radial slot cut from one end to the other to create a thick C-shaped cylinder. There are several reasons why I've not tried this approach. Because of the presence of the slot in the concentrator, there's a substantial non-uniformity in the shape of the magnetic field inside the concentrator that creates non-uniform shrinkage forces between the coin and the concentrator in the area directly beneath the slot. This causes a noticeable "kink" in the shrunken object at the location beneath the slot in the concentrator. While this often does not matter for many industrial applications, it is very undesirable from an esthetic standpoint for coin shrinking. There are a couple more subtle reasons as well. Joule losses within the flux concentrator mean that significantly more energy (60-80%) needs to be applied to the work coil in order to obtain the same degree of shrinkage forces. This means that the capacitor bank must be charged to a higher initial voltage before each shot. However, because a robustly built larger diameter work coil would no longer disintegrate, the capacitor bank and spark gap would now see a complete ringing oscillatory discharge. A high-Q ringing discharge is very stressful on both the capacitor bank and the trigatron switch (spark gap). To insure survival, the maximum voltage rating of the capacitors in the bank must be at least twice the maximum charging voltage to prevent overvolting the capacitors during voltage reversals. Also, significantly more energy is now dissipated within the spark gap since it is the main lossy component in the discharge path. Energy that was previously dissipated in the exploding work coil and plasma ball is now expended in evaporating the main spark gap electrodes and more frequent tear down and maintenance of the trigatron. Expendable and inexpensive magnet wire work coils only take about 30 seconds to wind, so I've chosen to use this approach instead of making major design changes to the system and fabricating custom flux concentrators. However, if coin shrinking ever became a high volume enterprise, I'd definitely reconsider the possibility of using flux concentrators and heavy-duty work coils. Best regards, -- Bert --
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Re: Flux concentrator.
Posted by Ben on 4/23/2004, 1:00 pm, in reply to "Re: Flux concentrator." --Previous Message-- Not really, it's mostly a hobby but I eventually would like to go back and get my phd in physics, not sure in what area yet though. I wonder if you could make the gap smaller using some high dielectric material in the gap to prevent arcing. Or if "spiraling" the gap would wash out some of the asymetry of the field. Another option might be to have a second "secondary" of copper pipe. Keeping that from being "disposable" might be tough as well as the extra losses incurred. For the ringing, could you quench your trigatron using some electronics to detect the voltage crossing zero and a solenoid to allow atmospheric pressure in? Especially if the inlet air was directed at the main gap.
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Re: Flux concentrator.
Posted by Bert Hickman on 4/25/2004, 7:34 am, in reply to "Re: Flux concentrator." Hi Ben, Those are some good ideas. Doing some experiments in this area is on my (very long!) "To Do" List...:^) The Trigatron is presently operated at atmospheric pressure, It might be possible to flood the trigatron with a strongly electronegative gas under pressure such as SF6. Another option might be to include an exploding wire fuse in series with the work coil, perhaps immersing the exploding wire a strong transverse magnetic field to aid in blowout. Developing repeatable "opening" switches is notoriously more difficult than designing closing switches. Good luck and best regards, -- Bert --
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