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.

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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.

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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 proof 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
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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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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Fri Nov 15, 2019 6:00 am

Completed two new electrodes for the quartz insulator tube. Vacuum and gas ports will be on the side of the larger electrode(top pic) leaving the face intact.

The prior electrodes comprised of several pieces which undoubtedly caused small virtual leaks from threaded holes and such. The new versions are all one piece eliminating that concern.

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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Fri Nov 15, 2019 7:50 am

Shown below is a youtube vid of a recent test shot with the now retired Pyrex tube. It was a relatively low power shot with 300mTorr of air at 14kv / 1400 Joules. The orange afterglow is most likely borosilicate muck from the tube (sodium/boron) cooling down after the shot.

https://www.youtube.com/watch?v=hQMqVocktFI

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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Fri Nov 15, 2019 11:31 am

‪Newly machined electrodes and fused quartz tube assembly. A little more work needs to be done but this is essentially it. ‬

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Re: Columbus-I Pinch Tube Build

Post by Richard Hull » Sat Nov 16, 2019 11:55 am

This is a really interesting effort and that Quartz tube musta' cost a bit. Keep at it and I look forward to the continued effort. The video with that ghostly wisp after the shot was most intriguing.

The issue with all pulsed systems is that if the joule energy is significant, (often needed to obtain and measure fusion), is that the very item designed to do fusion is savaged horribly. In such systems, the build is the thing. Material science is often stretched to the limit and a bit of knowledge of it is demanded. You seem to have it in hand in your effort against mighty forces. It will be interesting to see which will prevail.

When I was working with water arc explosions, in the guns we used machined nylon at the breech with the electrode pressed into it. I would never get more than 3 shots, maximum, before the nylon would shatter due to the brisance of the explosion. I soon machined backup breech inserts so that the experiments might not have to wait for machining operations. The problem was lessened considerably when We started using formula one racing spark plugs that have no protruding points, but a flat face of steel and ceramic. Even these were only good for 10 shots each at $6.00/ plug. The beauty is that we had to thread the base of the gun and damaged plugs became a snap to replace.

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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Re: Columbus-I Pinch Tube Build

Post by Robert Dwyer » Sun Nov 17, 2019 4:21 am

Mark,

Great effort, it is really cool seeing this project come along. I can say from experience working with high-yield pinches impurities have a massive effect on performance, even when dealing with MegaJoule machines, one thumbprint on an electrode, one manufacturer sending a wrong type of glass or not properly cleaning, has an outrageous effect on yield. The quartz should be an improvement, but you may want to move away from it in the future. With a capacitor of that energy the current you can get running through your plasma will absolutely ablate silicon from the quartz tube through interactions with plasma itself as well as the assistance of x-rays from the pinch. Depending on the timescales of your pinch and the ratio of the radius of your the ablated silicon may have enough time to contaminate the plasma pre-pinch or during the stagnation.

As for pre-ionizing, I never have heard of people pre-ionizing a gas for a pinch where the tube is actually backfilled with ambient gas. Most systems use a gas puff injected into a small plasma gun that forms a jet propagates into the region of the electrodes and is then pinched and is used with great success (I.E. the Z-Machines 1e14 DD neutron shots). On DPFs groups such as NRL have also puffed in gas (cold or pre-ionized) through the anode axially to form the target for the sheath. They controlled the shape of the target using various nozzle designs.

If you want to keep the backfill and pre-ionize the gas and then give it a smaller 'pinch' to move it from the walls you could try ionizing it with rf and have a small external coil that would create axial field that would induce current into the ionized gas and pinch it. Of course this raises a concern that you may actually stabilize the main pinch with the axial field, reducing M=0, and kink instabilities that will serve as the seeds for beam formation in the pinch and therefore reduce neutron production. Doing any sort of pre-ionization and pre-pinching may also worsen the contamination issue as now any silicon being ablated from the pre-ionized plasma will have a longer time to make it to the pinch and potential contaminate the pre-ionized gas before you begin the main discharge. If you want to keep the pinch-wall ratio the same then injecting pre-ionized gas me be a better option.

Of course experiments will show whether or not such concerns are founded. ICF and Pulsed Power is an incredibly fun field, but it does have its issues cleanliness and contamination problems being a major one. Depending on what you want your ultimate yields to be simply swapping out for the quartz tube may only be what you need, but looks like you are on your way to producing neutrons for sure!
If we throw more money at it, it will have to work... right?

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