Columbus-I Pinch Tube Build

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Re: Columbus-I Pinch Tube Build

Post by Richard Hull »

Of course, As long noted with pulsed, putt-putt fusion devices. The proof of fusion is best done with bubble detectors, or, if potent enough, activation efforts.

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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley »

Activation will be the first attempt followed by getting one of the bubble detectors. But I can’t imagine trying till i swap in the quartz tube.

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Re: Columbus-I Pinch Tube Build

Post by Robert Dwyer »

It would also be interesting to see the neutron and gamma pulse waveforms with a scintillator/pmt or perhaps some sort time-of-flight detectors. Of course that is easier said than done, but the waveforms of the radiation could tell you a lot, and with enough distance you could, based on timing of the pulses to the pinch, show separate gamma and neutron pulses which could also help prove fusion, besides Bubble dosimeters and activation. You could back out the energy spectra of the neutrons as well which would be interesting. I don't know too much about the dynamics of this design pinch, but im guessing that if you see any M=0 instabilities like in a plasma focus pinch, your fusion may come from beam target interactions which would give a slightly higher neutron energy spectra.
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley »

That would be a fun secondary project Robert. Once things are up and stable I may give it a go.

For a future iteration, I'm considering a moderately scaled down version where I can increase the cyclic rate of the discharges. While maintaining 30kV, I'm pondering how low in pulse cap value I can go and still generate detectable neutrons. Similar to the smaller volume Fusors (eg. 2.75 cross), maybe dropping the volume from a 17" long / 2" dia quartz tube to a 8.5" / 1" dia tube will allow for unexpected adjustment, hence the possibility of 5uF or considerably less. If the cyclic rate was high enough, detectable neutrons below 1uF may be possible. As indicated earlier by many, a bubble detector would be the best detection method for such a putt-putt type system. I can only imagine the electrical QRM and havoc it would wreak on normal detection gear at 20pps or greater.

Regarding my current (original) arrangement, I'm hoping to test it with air later next week. Deuterium soon after followed by the quartz tube upgrade.

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Re: Columbus-I Pinch Tube Build

Post by Richard Hull »

I agree. With a smaller volume, tube the discharge current should increase, if all other factors held constant (same as with cylindrical wire diameter.) rather rapid rep rates with a proper switch can work well with 0.5uf in a low inductance circuit.

As activation will save a lot of money over Bubble dosimeter costs, the system needed to get detectable activation will demand a lot from the experimenter in controlling the savaging of the tube's internal environment, allowing it to function long enough to attain suitable activation.

Note!! With any pulsed-discharge system at elevated voltages the X-ray pulse will be fearsome!!! Remember!!! The voltage of the discharge determines the x-ray energies. The current determines the number of x-ray photons produced, (intensity of the x-ray blast). There is a vast gulf affixed between 30kv @10ma and 30kv @3,000 amps! The actual dosing to a human, on a pulsed system, is a function of rep-rate and current in each pulse.

Be mindful of shielding and the inverse square law in this type of experiment as it is, as usual, all about safety from X-rays and not neutrons.

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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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley »

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 »

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

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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.

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Re: Columbus-I Pinch Tube Build

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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.

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Re: Columbus-I Pinch Tube Build

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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.

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Re: Columbus-I Pinch Tube Build

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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

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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

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‪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

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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.

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Re: Columbus-I Pinch Tube Build

Post by Robert Dwyer »

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!
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Re: Columbus-I Pinch Tube Build

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Just a quick update. Installed the tube and it passed vacuum testing with flying colors, so this evening I decided give it try with deuterium.

My first attempt was to test it at 15kV with 300mTorr of deuterium. The shot went off fine but a diode blew out on the charging supply causing damage to the transformer. Not a big deal as I have replacements on hand and should have it going again in the next several days.

After the shot I examined the cathode and noticed fairly good evidence of a pinch. The axial base of the pinch column left a diffuse half inch diameter mark along the edge of the electrode. The mark is significant enough that after a few 20-25kV shots the electrode will probably have to be replaced. The lab reports from the mid 50’s mentioned aluminum had a short life span. I may also try adding a thick stainless cover plate on the electrodes as a way to extend its lifetime. Another concern is the pinch column forming near the edge of the electrode (see pic). In the next design iteration I’ll machine it to have a raised center to see if that will keep the column from the edge. But, before any of that I’ll put this version through the paces.

Robert, thank you for your input. Cleanliness was the top priority during assembly and all looked good. Regarding the pre-ionizer, one of the old lab reports speaks of one with a linear pinch tube. Very little details so I can’t add too much on what specifics were employed.

Mark Rowley
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Re: Columbus-I Pinch Tube Build

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Great work Mark! Based on Robert's remarks, Pinch work is critical and tricky. Lots of stuff to learn, most of it, the hard way...

The heavy ablation is to be expected. Any significant high joule arc discharge, in or out of vacuum, regardless of gas will see this. Naturally, you had aluminum vapor as ions in the tube during the shot. The time ordered effects of all of this on the shot are relative unknowns at this point. Could you detect any deposition on the quartz walls? What did the current waveform of the shot look like?

I had to dump exactly $1,079 into my work on the water arc gun to obtain a 1000:1 Pearson RF current transformer. It was well worth it as it really told the tale on shots. Pearson really has that market as they have the secret behind not letting the thing ring up on its own to any significance on huge pulse discharges.

I also used the plus ultra Pearson on hydrogen thyratron driven Tesla magnifier systems with peak base currents on the order of 6,000 amps. I found that almost 100% of the many H2 and D2 thyratrons I found surplus were fully functional. Most are pulls from radar modulators or time critical, repetitive pulse apps where jitter becomes untenable to the app over time. This is never the case in low rep rates under 100hz and absolutely irrelevant in single shot switching.

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Re: Columbus-I Pinch Tube Build

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Thanks Richard. Tim Koeth put me on to a few Pearson current monitors that I may be picking up soon. Until then I don't have any waveform photos. I know this is of critical importance and it's top priority once I get the hardware issues sorted out. In Duniway and Phillips 1958 report "Neutron Generation from Straight Pinches" it's shown how the waveform can accurately predict if a shot generated neutrons and in some cases, yield. Neutrons are cool, but diagnostics will be the best part of this.

No indication of deposition on the quartz, yet. Undoubtedly this will change as I produce more shots.

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Re: Columbus-I Pinch Tube Build

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Still ironing out some bugs with triggering but I was able to fire it four times today. For now I’m still running low power (14kv / 1400 Joules) but that should change in the next few days. Todays shots ran 300mTorr of deuterium so I had the bubble detectors attached in the off chance.

Regarding D2 pressure, the old Sherwood reports cited everything from 100 to 500mTorr of pressure. When I start pushing this beyond 20kV I’ll probably start at 100mTorr and work upwards.

Mark Rowley

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Re: Columbus-I Pinch Tube Build

Post by Cai Arcos »

Mark:

The system you've built is extremely impressive. I want to express my gratefulness for posting such a detailed account online. If time and money allows me to, I might try to start something similar in the summer vacations of university.
If you would like to read more about pinches and fusion and general, I feel obliged to recommend one of my favourite books: Controlled Thermonuclear Reactions, by Glasstone and Lovberg. I myself have the 1960 and is superb! (In fact, I think is a book recommended in this forum).
You can consult the book in question here: https://archive.org/details/ControlledT ... ns/page/n7

Cheers:
Cai
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Re: Columbus-I Pinch Tube Build

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Thanks Cai for the kind remarks. That book is great and I too have a copy. I wish the forum here had the ability to store pdf's as I have a significant library on original Project Sherwood, linear pinch, and Sceptre / toroidal documents from the 1950's. Many from the big names like Colgate, Ware, Hagerman, Pyle, etc.

It's a very fun project which is somewhat heavy on the fabrication end. Nothing all that complex but most of the parts have to be custom built. One of my goals is to see how low in capacitance I can go and still achieve detectable fusion with the BTI. That's where the smaller pinch tube will hopefully make it's mark.

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Re: Columbus-I Pinch Tube Build

Post by Cai Arcos »

Mark:

Being more theoretically inclined, I am very interested in the library you have mentioned. If I gave you my e-mail, could you be able to send me your references?

I am also very interested in your investigations regarding capacitance, but mostly because in my case they would have to be home made rather than actual pulse capacitors, which would make stray inductances very tricky I suppose.

Cheers:
Cai
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Re: Columbus-I Pinch Tube Build

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Cai, if you’re on Facebook I have almost all the docs uploaded to the Nuclear Fusion and Plasma Research group. Easy to download.

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Re: Columbus-I Pinch Tube Build

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I had Facebook completely forgotten (had no picture even).
Just searched the group you've mentioned and it looks amazing!
I'm gonna tidy up a little bit my profile and join.

Thanks for the recommendation!
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Re: Columbus-I Pinch Tube Build

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After last weeks success I quickly identified a few areas that need attention. Since the next phase of testing will be in the 30-40kv range, I’ll need to add some insulation around the central capacitor lug so flashover doesn’t go to the case. I’ve seen that happen to some quater-shrinker folks with some disastrous results.

The spark gap will need some safeguards installed to insure unexpected triggering doesn't occur. During that mod a system will be constructed to allow me to adjust circuit inductance.

D2 feeding has been tricky with the valve I was using so a medium flow SS-4MG will replace it next week. (As a side note, I’ll be installing another SS-4MG on my Fusor to compliment the SS-SS4).

Another modification for a little later will be a slight redesign of the electrodes. The anchoring points of the plasma are forming along the side of the anode putting it within a few mm of the glass wall. My plan is to modify both electrode faces by machining on a gradually raised node in the center. I’m hoping that should anchor the plasma to the axis...or at least help. This doesn’t imply a strategy to ward off instabilities as thats a whole different ball of wax, not to mention impossible with this arrangement.

Lots to do and with some luck I may be able to fire off some more shots by the weekend.

Mark Rowley
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