Jim Kovalchick -My attempt at smaller fusor

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Jim Kovalchick
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

Some interesting and bothersome results. At 38 kV and 10 mA I recorded roughly 750,000 neutrons/sec. I noticed that it appears that my neutron probe saw significantly more neutrons at the lower end of my chamber corresponding to one end of the beam. There were some on the opposite end but not as much.

I also noticed my chamber outgases a lot as it heats up. I think maybe it's my titanium grid.

I did a second run at 38 to 40 kV later today and neutron numbers were way down. Even pictures I took were noticeably less speckled. I moved my gas to throttle ratio to flow more d with no improvement. Hmmm.

I have an idea for a new grid design that does not involve titanium and has only one opening...a cup grid. This will have to wait because it's back to the grindstone for me.

Jim K
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Jim Kovalchick
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

With poor results from my last grid I decided on another approach. This time I used a coil of tungsten braided wire. This grid does not make a tight beam, but I'm happy with the proof of concept. Some minor design modifications should fix it.

Jim K
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Richard Hull
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Richard Hull »

Did you get that twin braided W wire from the "orphan pile" at Midwest Tungsten? I picked up 20 strands a few years back of that double twist wire and it has been the grid in fusor IV for about 5 years. Works great!
I enjoy your reports on your project and the issues with the system. It will help me a lot.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

Richard,
Yes, from the orphan pile. Sadly, it appears that the orphan pile web page is gone. I gave some of my pieces away and still have a few. They are perfect for our work.

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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jon Rosenstiel »

Jim,

As to outgassing, was your titanium cathode pure Ti or an alloy? (The one I made was an alloy, 6Al-4V)

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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Richard Hull »

Good Question Jon! I have some 3n6 1/2" rod stock. The alloy sold by many suppliers is to allow for a more machinable product without hampering strength.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jim Kovalchick
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

Jon, I wouldn't be surprised if it was, but I don't know if the titanium I used was an alloy or not. I bought a small sheet of it at a past HEAS. I think from T.R. Leary.

I'm away from my lab for a while now to check, but I think the sheet had some numbers and/or letters etched on it.



Jim K
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

Trying yet another grid. This one is a simple piece of stainless tube. Not a lot of neutrons yet.
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Richard Hull »

Absolutely lovely!! Too bad about the lagging neutron production. I am glad good old fusor IV is standing by just in case fusor V disappoints me. I have just finished mounting my Turbo, (positioning it and bolting it into place). I hope to test it at its head soon. My fingers are a bit numb in the 35 degree lab. If the turbo disappoints, well, I have the diff pump all cleaned and standing by as well. It is all wait and see while giving the system every opportunity to shine.

Jim, I hope your system climbs over time. Hopefully, some wall effect D2 absorption can work its way into climbing numbers in your system.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

Thanks for the words of encouragement Richard. I'm sure the numbers will come up. Best of luck with your next fusor. Spring and warmer temps are coming soon!

Jim K
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

Here is fusor 'outtake '. Arcing from my recent grid while it was conditioning.
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

I made a major discovery about why my fusor results were lack luster. A hot connection on my power supply was taking up a lot of the current flow. I corrected the connection and now getting lots of neutrons and my grid heats to red at 6 mA. I did not discover this issue before because I measure my current at my XRT. This picture was taken at 28 kV and 6 mA. Not that I'm happy to see it glow red, but this is more like I expected before. If you zoom in, my phone's picture is very speckled.
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Richard Hull
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Richard Hull »

Nice picture! I like the red glow. Looks like real power is expended, but that is what fusors do. Too many want power out, but that is not what happens.
I hope to have fusor V on line this spring. I have some ideas that might, just, with some luck, amount to nothing.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Mark Rowley »

Nice to see it cranking out some good results and am looking forward to seeing your neutron counts.

Fwiw, that's close to the same input numbers I've attained with the 60kV precip supply.

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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

An update and a problem.
Update: At 40 kV and 5 mA I am getting roughly 1 million neutrons per second at one end of my cross. Definitely seems neutron readings are stronger at the ends of the electron beams.

Problem: Not a new issue, but as I encounter new voltages, there is initially some arcing until it cleans. With higher voltages, the transients on the system have become more severe. I have fried a couple harbor freight meters and a vacuum gage controller. I also noticed some arcing between hv connections and the shield ends pulled 8 inches back on the ends of the xray cable I am using. I read a paper last night warning about ungrounded ends of shields on xray cables especially where the cable long and coiled. Because xray cable is precious I had been reluctant to cut it. Today I cut 25 feet off it, used only the length I needed, and grounded both ends of the shield pulled 8 inches back from the ends. I did a run in this configuration and found that the few arcs inside the chamber caused less audible noise and my meters recovered quickly until one last arc killed another harbor freight meter. I have this one looking at current by looking at the drop across a 10 ohm power resistor in line with the ground from my XRT. This spot has killed three meters so far. I'm not sure what else I can do.

My power supply is a beefy XRT with a ballast resistor but no cap. The xray cable goes to a voltage divider bucket and then right to my feed through. My terminations are wrapped tight with multiple layers of kapton. I get a slight hiss at the end of the ballast resistor connection at 40 kV but no snapping. My transients start as just grid cleaning arcs that sometimes turn into transients.

My chamber is grounded into a star point which then terminates into a wall box copper ground.

Any ideas are welcome.

Jim K
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Bob Reite »

The 10 ohm current sample resistor is a nasty point for transients. During an arcing event, that point tries to go to a very high reverse voltage. I lost a digital meter there. After that I installed 10 K series resistor in the ungrounded side going to the DMM, then put a 10 volt TVS diode across the meter connection. I had the TVS diodes on hand, as I use them for a similar purpose in vacuum tube transmitters at the cathode current sample. After doing that, the meter would still sometimes get "goofy" but at least it wasn't destroyed, power cycling the meter would bring it back.

If you can't get TVS diodes readily you can make two pairs of silicon diode strings. Figure out the maximum normal voltage you expect to read, then divide by 0.6 to get the number of diodes you will need. Hook the two stings in parallel back to back, this will give protection for a transient going either direction.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

Bob,
Thanks for the suggestion. A little arcing is to be expected so a circuit that is more tolerant is a better approach.
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

Bob,
I'm assuming a bidirectional tvs diode would eliminate the need for two diodes across my resistor. Is this correct?
I also wonder if the breakdown voltage value of the tvs is that important in an order of magnitude or so because I expect that surges of concern will produce higher voltages very fast and the tvs will react quickly.
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Bob Reite »

Yes. a bidirectional tvs does eliminate the need for two devices. I would choose a breakdown value about twice the highest voltage you expect to read under normal conditions.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

My neutron numbers have been dropping steadily over the last several runs. Today I took a series of measurements at various voltages from 30 to 40 kV with constant current. After I was done I went back to my starting voltage and repeated the measurement. The difference was huge. At -30 kV, 5 mA, and a starting beam end chamber chamber shell temperature of 88.9 degrees, the BF3 tube saw 230 counts in a minute. Same voltage and current, but starting temp of 150 degrees, the counts in one minute were down to 140.

Even my initial numbers today were half what they were a week ago. I suspect my grid and/or chamber must have experienced some changes. Perhaps I have driven my stainless steel grid to temperatures that caused accelerated plate out that is reducing absorption of deuterium in the chamber. I think it's time to open it up.
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Re: Jim Kovalchick -My attempt at smaller fusor

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Same here, the readings are dropping here as well. I never got even close to 100kn/s. Flash arcing will advance any neutron counting by >2k counts instantly, ruining the count run. Several arcs have been EMI powerful to the point that they have shut down the turbo supply (safety feature). (controller not hurt). I have popped the fusor supply breaker twice is severe arc conditions.

It is now fully decided to totally abandon the cross fusor as a rather worthless project for a guy like myself used to 1 mega neut/s with no sweat and no hassles. As I already noted the cross might do great for newbies looking for a quick win. I am going back to a modified fusor IV which will now take on the fusor V moniker in replacement. No light at the end of the cross tunnel save for that due to arcing which limits the top end. Give me the HV clearances and even electric field distribution, large surface areas for D2 absorption and desorption found in a sphere.

Keep up the reporting Jim. I can feel your pain. Sadly, this was the fastest pumping and best sealed system I have ever worked with. From dead start of the mechanical pump to sub micron in under 60 seconds!!

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Frank Sanns »

What is the goal here; high neutron numbers or understanding how these contraptions work? It is an important question.

In my iterations of multiple grid electrodes, needle points, plasma electrodes, reverse polarity, non symmetrical, and the like, there is a different set of operating conditions that gives the highest neutron output. Some are paltry outputs and some are much more robust.

The standard fusor, made in a reasonably large chamber, is a near foolproof way to get good neutron production. With it comes limitations. One is that there is a unique highest current that can be put out at a given voltage with a particular configuration. That in itself says that things are not a simple as they might appear.

In the smaller fusors, alignment of these non traditional setups are going to be super critical. A miss in a big fusor is nearly negligible. In these smaller fusors, alignment will need to be closer to laser cavity mirror alignments than the big ole wire grid fusor.

As for flash arcing, try rounding off some of the edges and cut them back a little to give more relief.

Don't give up. Be more observant and more meticulous in your methods and you might be rewarded some very good neutron numbers.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Frank Sanns »

Jim,

Somehow my post response to you was lost. I think you may have deleted your post while I was responding. Here is another try.

No insult intended to you or Richard. My post was more directed at the new work that Richard is doing. I just did not want him to give up.

When I was out visiting Jon Rosenstiel a couple of months ago, we looked inside his cube. It was very clear that some micro mechanism was going on there that is not normally seen in a conventional fusor. I simply was trying to convey some of that info to add to the data base. I know you are Richard are extremely throughough. No insults or demeaning intended. None. Zero. Sometimes I just write and forget the "tone" on a technical forum. My bad. Keep up the good work!
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Jim Kovalchick
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick »

No worries Frank. I reconsidered my response because I am aware that written posts shouldn't be looked at that way. I appreciate your contributions to my efforts.
Best regards,
Jim K
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Mark Rowley »

Fwiw, I went through a multitude of grid sizes before I found the sweet spot with one of 0.45” diameter. I started with one around 0.85” and experienced many of the problems you and Richard have pointed out. Once the 0.45” was installed everything began running smoothly. Other than that, I do use an alumina insulator for the stalk and my grid is tungsten. And of course it’s a classic grid and not a tube design.

Input power seems to be a bit different as well. 10mA input seems excessive, at least from what Ive learned with mine. 3.5mA at 45kV with ~35mTorr of D2 should easily put one at near or over the 500k n/s range. With my system, 10mA at 30kV would only serve to overheat the grid to astronomical levels. If you haven’t yet, try raising the flow and pressure of D2. Strive for higher voltages (40-50kV) with current draw below 5mA.

Mark Rowley
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