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 Nov 20, 2019 7:37 am

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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Richard Hull
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Re: Columbus-I Pinch Tube Build

Post by Richard Hull » Wed Nov 20, 2019 2:59 pm

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.

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 » Wed Nov 20, 2019 5:51 pm

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.

Mark Rowley

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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Tue Nov 26, 2019 5:53 am

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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Cai Arcos
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Re: Columbus-I Pinch Tube Build

Post by Cai Arcos » Wed Nov 27, 2019 1:48 pm

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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Mark Rowley
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Wed Nov 27, 2019 6:08 pm

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.

Mark Rowley

Cai Arcos
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Re: Columbus-I Pinch Tube Build

Post by Cai Arcos » Wed Nov 27, 2019 6:22 pm

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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Mark Rowley
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Wed Nov 27, 2019 7:12 pm

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

Mark Rowley

Cai Arcos
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Re: Columbus-I Pinch Tube Build

Post by Cai Arcos » Wed Nov 27, 2019 7:34 pm

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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Mark Rowley
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Mon Dec 02, 2019 6:06 am

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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