Columbus-I Pinch Tube Build

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Mark Rowley
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Wed May 29, 2019 6:30 pm

Excellent and most appreciated warning about the xray issue Richard. An added benefit of the smaller size will be the ease of encasing it within the multitude of 26lb lead bricks that I currently have on hand.

Mark Rowley

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Mark Rowley
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Sat Jun 08, 2019 8:07 pm

Here’s a quickly pieced together concept for a smaller, high cyclic rate pinch tube assembly. Ill probably start construction on this sometime in July.

Mark Rowley
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Thu Oct 24, 2019 6:16 pm

Just a quick update on this. I’m still slowly progressing towards a test shot very soon. Working on the Fusor and domestic projects have recently taken priority, so this got the back seat for awhile. The other hangup is pulse neutron detection which leaves me with either a costly BTI purchase or the use of CR39 plastic. If I use CR39, I plan to use the Fusors neutrons to establish what I should be looking for in the plastic after a pulse shot. The only other method would be activation but I’m concerned that such a cyclic rate will exceed the thermal limits of my pricy fused quartz discharge tube.

I still plan on firing the larger tube I built in the beginning of the year but this smaller one will be first. Currently waiting on a special KF25 fitting and a needle valve.

Mark Rowley
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Re: Columbus-I Pinch Tube Build

Post by Richard Hull » Thu Oct 24, 2019 11:31 pm

Thanks for the update. If you get your pinch tube working it will be the first attempt to actually use a pulsed fusion system (putt-putt) here at fusor.net. You are very wise to be concerned about neutron detection issues with pulsed fusion. I would say that doing it right would be one of the most difficult tasks facing you. The issue is it would have to be bullet prove and really believable. (neutron rates). I would go with either activation or the absolute unassailable results would be the BTI route. As you say, that is expensive and the activation route would require long term pulsing which might force undesirable thermal thermal issues on your system.

All the best in a tough situation. You will be the pioneer here for all of us. I anxiously await running reports of this interesting pulsed system. The radiation reports can come once the operation is well in hand.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Mark Rowley
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Thu Nov 14, 2019 3:39 am

While waiting on some parts for the small unit I decided to resume work on the big tube posted about earlier in this thread. Also, since I took delivery on a bubble detector, that leaves me about 4 months to conduct every test at my disposal before it expires.

Capacitor charging circuit was finally assembled allowing a full 11k Joule charge at 40kV in about 1 minute. Once done I spent two afternoons putting the disposable / interim Pyrex insulator through all the motions. In addition to a couple dozen low power shots with air, I attempted 4 shots with D2 at known fusion inducing power specs. Those being 300mTorr deuterium, 28kV, 5500 Joules) As expected, the Pyrex tube was not suitable for generating a detectable level of fusion reactions. The sodium and boron in the glass mixture poisons the plasma causing a variety of problems. Pinch duration is reduced by the hot plasma conducting along the Pyrex walls. In doing so, more boron and sodium shears off into the plasma poisoning it. All of which was indicated in the original Los Alamos and Livermore tests in the mid to early 1950’s. Using fused quartz essentially annihilates these problems and increases the neutron/fusion yield by 100 times (also stated in the Livermore and Los Alamos reports). Fused quartz being somewhat expensive, I decided to first use Pyrex for prototype / stress testing purposes. It served well and much was learned in the process.

I’ve also been entertaining thoughts of a pre-ionizer which was used in the earlier systems. Establishing a small pinch effect to remove the plasma from the walls prior to kicking in the main charge has proven to be a valuable addition. Can’t find much info on linear pinch pre-ionizers so this may take awhile to learn about. No doubt there are a ton of specifics to making it work.

After the last shot, I noticed some slight scoring or fracturing along the circumference of the tube. When I removed the tube from the return conductor it was evident the scoring was extensive and went the entire length of the tube (see pic). Interestingly, the small fractures are actually a pattern consisting of a multitude of circles that go around the circumference of the tube from end to end. This effect is not deep and only localized to depth of a mil or less on the inside of the tube. The outside is still like new. There are no lengthwise or linear fractures along the tubes axis. Interesting effect that I have little explanation for.

The higher powered shots seemed like they have the possibility of adding physical stress to the tube. So to remove any chance of that contributing to a catastrophic fracture, I’ll be moving the spark gap away from the tube. It should also allow for an easier design to add or subtract inductance and install a Rogowski coil.

So far this has been an equally fun and educational project as the Fusor.

Mark Rowley
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