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 » Fri Feb 21, 2020 11:34 pm

It’s been awhile since I updated my progress so here’s the latest. Following a very generous offer from Jon Rosenstiel, I was able to upgrade the capacitance of my system from 14uF at 40kV to 56uF at 40kV. Its present configuration stands at 42uF.

In addition to the capacitance, I upgraded the electrodes with a 0.25” stainless steel cap to reduce wear and tear. After about 25 shots they seem to be holding up well except for a dark sputter buildup. The quartz tube doesn’t seem to be getting sputter buildup....yet.

Another upgrade included the addition of a quick change post for the circuit inductor. This allows for some basic adjustments to the discharge waveform. Monitoring the waveform is still a work-in-progress. I hope to have some pictures in the near future.

Results...
After discovering the ultraviolet interference with the BTI bubble detectors, I have since blocked the UV by wrapping the detectors in thin lead sheet and placing them along the tube opposite of the spark gap. They are also insulated from mechanical shock, although there really is none to speak of.

As of today I am registering on average 1 bubble per shot with the shielded detectors approximately 7cm from the plasma column. Results are consistent regardless of where the detector is placed along the tube. Deuterium pressure averages 275mTorr and voltages have been between 17kV and 22kV. Circuit inductance is ~0.14uH. Increasing inductance past 0.30uH results in a neutron yield too low to detect.

Future work will be to replace the quartz tube with one from a more reliable supplier of pure quartz. The one I’m currently using is from an eBay source who stated the origin was from China. I’m not totally confident of its purity or if it has boron content. Im also assembling a Rogowski coil for diagnostics. In the meantime I’ll experiment with the operating parameters in hopes of increasing the neutron yield.

Mark Rowley
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Richard Hull
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Re: Columbus-I Pinch Tube Build

Post by Richard Hull » Sat Feb 22, 2020 12:15 am

I am glad to see you are back at it and in the game. Very nice set up, indeed!

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.

Jon Rosenstiel
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Re: Columbus-I Pinch Tube Build

Post by Jon Rosenstiel » Sat Feb 22, 2020 2:15 am

Mark,
Great to see these caps finally getting some use. Nice work.

Jon Rosenstiel

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Mark Rowley
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Re: Columbus-I Pinch Tube Build

Post by Mark Rowley » Sat Apr 04, 2020 4:16 am

Over the past couple weeks I swapped out the pinch tube with certified fused quartz from a reputable supplier. I also machined two new electrodes to accommodate the slightly different tube size as well as to move the D2 inlet to the bottom electrode.
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After vacuum testing the entire arrangement I was pleased to see the 1402 pull an 8 mTorr vacuum after about 10 minutes of pump time.

I conducted a total of 6 shots (two sets of 3) with no neutron detection from the UV shielded bubble detectors. The first set used a small 1” Drierite column in line with the PEM cell D2 reservoir. I ran the shots at exactly the same parameters which on average had previously yielded 1 bubble per shot. That being 20kV, 42uF, 300mTorr of D2. Since the Drierite column has proven to be somewhat inconsistent, I decided to test this exact same D2 input configuration with the Fusor. Interestingly, the Fusor could barely get the neutron detector to register over 150cpm. After removing the Drierite, my neutron detection shot up to almost 5k, which is essentially normal operation. Drierite was just not going to work this time. I’m still thinking the stuff is just too porous and filled with air to keep the D2 purity at its maximum level. As with the previous forum post about Drierite, I also dumped about 32mL D2 into the tube as an attempt to purge it of air. No obvious leaks; it just wasn’t going to work.

The second set of 3 shots used straight PEM cell deuterium from the reservoir. Still no bubs but I noticed a couple other factors which may be at play. Firstly, the stainless steel electrode caps tend to quickly load up with a quartz deposition layer. The layer is thick enough where surface conductivity is nil. This wasn’t the case when I was using aluminum. But the aluminum tended to wear out quicker so I tried stainless this time. Physically, stainless holds up well but the quartz buildup is a significant problem; especially if it gets bad after 6 shots. Fwiw, none of the original machines at Livermore or Los Alamos used stainless steel. Seemed that it was almost always aluminum. I’m also wondering if the chromium, nickel, and carbon content in the SS is somehow poisoning the pinch.

Another negative issue I noticed was with the plastic spacer / stabilizer ring I had between the quartz tube and the copper return conductor. In the below picture, it’s clear there is a plasma buildup in that region has caused a darkening of the glass. Undoubtedly this is negatively affecting the pinch and I’ll be removing it for future shots.
D14D2E01-E58E-4B09-8BA1-2ED53B371FC0.jpeg
This picture is the lower electrode after 6 shots. Note the brownish glass-like material deposited on the stainless steel. Also of note is the ablation strike mark near one of the stainless anchoring screws.
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The upper electrode shown here has a nice centrally located ablation mark. There’s practically no evidence of the plasma pinch column anchoring at any other place on the electrode. The main difference between this electrode and the lower is that it’s totally contained within the copper return conductor pipe. The bottom electrode extends several inches below the return conductor. The non-centrally located strike mark on the bottom conductor may be due to the plastic ring disrupting the linearity of the plasma column possibly by some sort of capacitive effect.
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After making these adjustments I may add a two loop pre-ionizer as shown in this illustration. The old Livermore team insists preionization is required before any significant neutron yield is realized. Other teams tend to disagree.
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Eventually the spark gap will be replaced with a nitrogen trigatron. Unfortunately, by the time that’s done my bubble detectors may be long expired. :/

Mark Rowley

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Re: Columbus-I Pinch Tube Build

Post by Richard Hull » Sat Apr 04, 2020 6:40 am

Nice continuing effort. First rate. Sorry about no neuts. You would think that there would be some at such peak pulsed powers. This would be thermal fusion, I would think, due to the density and plasma heating.

Keep up the effort. Too bad about the life span of the BTI bubble detector.

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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