Archived - University of Utah's new demo fusor

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Chris Roberts
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Archived - University of Utah's new demo fusor

Post by Chris Roberts »

So, in August of last year I made my first post to the forum, and began collecting parts for my own fusor. During the following school semester, I was talking to a professor in our physics department at the University of Utah, and mentioned the fusor project I was working on. After showing him the fusor website and photos of other’s fusors, he thought it sounded like a neat project and asked me if I wanted to build one with the college, to be used as a demonstration tool. It did not take me long to say yes. =) He acquainted me with Adam Beehler, the lecture demonstrator for the physics department, and he and I started amassing parts for the university. Thus, for the past year Adam and I have been scrounging and working on a bell-jar fusor for the university, while I have been working on a stainless steel version that will stay at my house.

Needless to say, the college has better resources than I, along with a far vaster “junk box”. For example, Adam and I were discussing about where to acquire deuterium, and were wondering if we needed to buy a regulator as well. Adam knew of an old tank sitting in his lab room that had a regulator, so we dragged the tank out to take a look. To our surprise, the tank was labeled “deuterium”. Sure enough, they had deuterium practically just lying around not getting used! We then talked to the guy who first squirreled it away, and from what he remembers it is a leftover from one of the many cold fusion experiments that made the U of U so famous a while back, so we get to take a little piece of our university’s history (infamy?) and finally get some of those atoms to fuse properly. =) Anyways, considering all this, the university’s fusor progressed a lot faster than mine, and is nearing completion. So, I figured we would post some images of our work.

The first picture is a composite of the fusor setup itself, along with it running with the lights dimmed. You can see the bell jar on the top, which goes down to a thermocouple and cold cathode gauge, then to a segment of pipe housing a simple homemade baffle, past a big throttle valve, down to a cute little diffusion pump. (The oil charge in one of these little critters is only 20mL…) Backing the little diffusion pump we have a beast of a roughing pump, which is kind of overkill, but that is what we had on hand. Inside the bell jar, we have an upside-down 4L beaker to act as a sacrificial shield for the bell jar. (In the picture you can see it is broken, this was from a non-operational accident) When we get our higher voltage power supply we will either replace the beaker with a metal can for the proof of concept runs, or possibly, if the sacrificial beaker can handle the heat, continue to use a (non-broken) Pyrex beaker along with a liberal application of leaded glass. We will have to see on that one.

Second, we have a close-up of the bell jar during operation. First light was sometime around the start of August. When we got our bell-jar base and manifold back from the welder to fix the two leaks we had found, we did not have a proper outer grid made and really wanted to see some plasma, so we just wound a very crude spiral around a pipe and allowed this mutant slinky to stand under its own weight, merely resting on the bell jar baseplate. We haven't got around to changing it yet, as functionally it works great, so once everything works we will replace it with a prettier version. Also, you can see that for our connection to the inner grid to the HV feedthrough, we just used a banana plug tube, which had a plastic covering. This later proved to be mildly disastrous, as during one run, the plastic swelled up and deposited crud all over the beaker. (We were glad it got on the beaker and not the bell jar.) One thing in particular we saw during our first few runs was that the bugle jet would rapidly flicker all over the interior. We caught a video of that, and I will try and post that soon too. It sure looked cool; it really made the thing look like it was going critical or something. =)

Third, a nice composite image Adam made of the fusor running at full NST voltage, at varying pressures. A couple of interesting things with this is that occasionally, if we are slow with increasing the vacuum, the plasma will start with the discharge to the baseplate, then slowly crawl its way up the grid, following the wire around and around, until it looks like the 1000 millitorr example. Also, it is interesting how the lower discharge disappears after about 250 millitorr is reached.

Lastly, we replaced the plastic banana plug sheath with an alumina tube, cleaned the deposited crud off of the beaker, pumped the chamber down with the diffusion pump, let some deuterium in, and boy, that just looks awesome. This is still at NST voltage, which we measured with a high voltage probe to be all of 500 volts when under load. Thus, we have no hope of fusion currently, but it is nice to see the color change from the differing gases. Also, our chamber is either outgassing or leaking a bit, as this nice pretty color does not stay for long, so we will have to work on that too. In this picture, I particularly liked the apparent shadows coming from the wire of the inner grid; perhaps the wire is shielding outgoing ions? This is my favorite photo we have taken to date.

So there you have it. This has been an amazing project to be working on; I owe a lot to Adam and Professor Ingebretsen for offering to let me do this with the university, I really cannot sing their praises enough. I have been able to learn a lot from this project that I am now applying to my ongoing fusor, and hope to have something tangible of my own by the end of the year. Anyways, enjoy the photos:
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Jet_800x600.jpg
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Richard Hull
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Re: University of Utah's new demo fusor

Post by Richard Hull »

Very nice images. The Meiro grid is being used more often now, I see. I hope the project might move on to fusion, but you might need a metal vessel for that.

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
Chris Roberts
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Re: Archived - University of Utah's new demo fusor

Post by Chris Roberts »

I think we are finally starting to figure out how one of these contraptions is supposed to work.

For a good month or so nothing much has happened, as we felt that our power supply was inadequate and couldn't find a better one. Whenever we would try and place any significant power to the fusor, the voltage would fall through the floor, and our current would jump up and the power supply would turn itself off. We just chalked this up to having a wimpy power supply. Finally, after reading a hugely informative post here regarding the fine balance needed between pressure and voltage, we started to get the idea that maybe we were still running things at too high a pressure. So we did another run to see how low a pressure we could get without the glow extinguishing.

At first, we did not have much success, as we were trying to regulate the pressure with the throttle valve, while leaving the gas inlet valve at a set, very low level. The plasma color was still blueish, so we did not have a good amount of deuterium in there, and the throttle valve's adjustment was far too coarse. We could either have the glow extinguish, or have our power supply give out. So, then we tried things from the other direction. We opened the throttle valve to the point where our thermocouple gauge would barely zero, then let a healthy stream of deuterium in from our needle valve to get the pressure to where we needed it. That made all the difference. The plasma turned this beautiful shade of red, and we could fine tune this valve much more easily, so we were able to push our voltage much higher. I had no idea that the plasma had to be kept so darn close to extinguishing.

We managed to get the voltage to about 16-17kv when our geiger counter started beeping away, indicating x-rays were starting to come through. So we turned it down a little from there. But, others have reported fusion starts at around 15kv, so both Adam and I feel optimistic that we have the right conditions for fusion now, all we need to do is get a good detector and find out. So there it was, ready to go, sitting around for a month, and we just did not know how to balance everything correctly.

Adam got a really good picture from this recent run. It is nice to compare to the previous pictures, as there is a good difference in the appearance of "demo mode" versus "fusion mode". (At least, what we believe is "fusion mode") The beaker we are using as a shield for our bell jar has a little ripple in the glass lower down, so that is why the feedthrough stalk looks so distorted at the bottom. Enjoy.
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Steven Sesselmann
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Re: Archived - University of Utah's new demo fusor

Post by Steven Sesselmann »

Chris,

Nice picture, and I would not be surprised if you are getting a few neutrons.

Good luck with the measuring.

Steven
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https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
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Doug Coulter
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Re: Archived - University of Utah's new demo fusor

Post by Doug Coulter »

Good move on the sacrificial beaker. If you've taken care to screen your vacuum inlet, it will save you some troubles later, and is cheap to replace. You can shatter these fairly easily btw.

One interesting observation we made here while doing a high power electron gun, and using pyrex for a target (glows nicely as a phoshpor) is that the target took a lot of abuse that didn't really show until we'd finished the experiments and had taken it out of the tank. After a couple days, the target area was covered with some white dust, which then deliquesed and wiped off. The only thing I can think of is that we "reduced" the compounds in the glass with the beam. You might see if the same thing happens here.

We did some tests here with spiral wound grids like yours. In not a lot of testing (this was a survey kind of thing) those were the worst of all the things we tried, little or no neutron output for the same conditions other grids were making plenty. Dunno if that was some other experimental variable, we'd tried nichrome for that one, and were using Ti for the others, but it's one data point in a vast number of them. I'd encourage you to try some A to B kinds of comparisons while controlling other things as much as possible and see what you see -- in this setup it would be easier to do than in most others, so work with the strength of what you have!

We have just barely seen neutrons at about 16-18kv, but the reaction rate zooms above maybe 35kv and seems to go up better than linear with volts from there to about 53kv (highest we've tested).
Above 40, we need lead on the SS tank, and the windows have long been covered with leaded glass.
Above 42kv, the leaded glass isn't enough, nor is the SS tank -- we used thick CRT glass from an old color picture tube, the pro stuff is probably better (and thicker).

So right now we're cutting and soldering lead for the complex tank so we can run again.
Why guess when you can know? Measure!
myID
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Re: Archived - University of Utah's new demo fusor

Post by myID »

Hi

really nice pictures of a nice clean setup!
I guess if you have a sensitive Neutron Detector and a supply just a little bigger (perhaps use a Variac and a 110V to 220V transformer to power the NST? do not fry it...) you will have the proof it works soon.
Also pretty cool to have a really nice "demo" i.e. Bell Jar Fusor actually producing Neutrons!!

Kind regards
Roman
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Re: Archived - University of Utah's new demo fusor

Post by Frank Sanns »

Chris,

Congratulations to your team. You are leaning a great deal and it all looks good!

An observation based on your pattern of blue fluorescence on the glass and the shadowing of the deuterium glow by your inner grid suggest that your inner grid is really hindering your chance of good neutron numbers.

The inner grid can be optimized much beyond where you are. There is so much wire area that the aperture to the poisor region is obstructed. In addition, the choice of grid design that you are using is about the very worst for blocking trans inner grid ion trajectories. There is not a clear path from one side of the chamber to the other hence little or no head on collisions and no "star" appearance. The appearance of the star is not important other than providing a visual indication of symetry of the opposing openings of the inner grid and really it is multiple recycle of live ions through the center with increased proability of collisions with neutrals but you get the idea.

If you choose to stick with the spiral grid, then thinner wire and half to a third the number of turns of wire will really improve things. An alternate to this is the Mobeus grid that also needs no welding.

Frank Sanns
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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: Archived - University of Utah's new demo fusor

Post by DaveC »

Chris -

Very nice work! And some very good pictures. From your quite nicely detailed description, you are clearly learning the ways of plasma.

The pressure balance indeed becomes delicate at the low pressure end of the glow discharge regime. It can actually go to quite low pressures and still give you ions, if you have enough voltage gradient around the outer electrodes. (Small wire diameter can help here.)

Keep up the good work.

Dave Cooper
Chris Roberts
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Archived - University of Utah's new demo fusor - we have fusion!

Post by Chris Roberts »

Well, I think we finally got it...

Over the past months, we have made a few changes to our fusor at the U of U. Following the recommendations here on the forum, we made a new inner grid which is much more transparent to incoming ions. At first the grid was silver-soldered together, which did not work well. Once the thing heated up in operation, the solder melted and the grid fell apart. Eventually we got a grid spot-welded together, and that has held up under the heat. After running for a few minutes the grid glows orange rather brightly.

The second change we made was to the outer grid, to make things more uniform and to also give the fusor a better overall appearance rather than the mutant slinky thing we had in there at first. This grid is made of regular stainless steel wire, and is silver-soldered together. The outer grid does not heat up nearly as much as the inner one, so this proved to be sufficient.

We got a new bell jar, due to us ignorantly trying to move the fusor from one place to another with the bell jar still on top. We hit a bump, the inner sacrificial beaker tapped the bell jar, and cracked it. Hopefully a mistake we will make only once. This new bell jar is much thicker than the other one, and weighs a lot more as well.

Thus, with all these new improvements, we now see a gorgeous star mode when running things correctly, see pictures below. The stainless steel fusors like the one I am building at home may perform better in the neutron department, but this thing certainly can't be beat for the visual appearance. In person you can move around the thing and see all the little star rays in three dimensions which looks really neat. Adam recorded some video of moving around the fusor and capturing the rays in all their glory, I will try and put it up online sometime soon.

Now for the fusion runs. We noticed that with the new bell jar, our Geiger counter does not start detecting x-rays until about 20kv. This is a little higher voltage than we could hit with the first bell jar, our best guess is that the sheer amount of glass we have on the system now due to the new bell jar helps shield the x-rays a little better. So, we ran the fusor at around 18kv for about 15 minutes, and did not see anything. It was some time before we learned that lower-yielding fusors may have to run for a while to see anything, so we did a run for about 2-1/2 hours, turning the power supply off whenever we felt the grid needed to cool down. At the end of the run, we looked at our detector and behold! Three bubbles! Yeah, that is not much, I know having a bell jar limits a couple conditions needed for the really fiery runs, but hey, we did it!

Here is some of the data on our run:
Voltage input: 16-20kv
Current input: 7-9 ma
Plasma run time: 2 hours approx.
Bubble Detector: 28b/mrem
Detector Distance: 6 in

Using Steven Sesselmann's fusion calculator we get a whopping ~1500 neutrons per second, with a very large uncertainty due to there only being 3 bubbles. The voltage, current, etc on our run are also very approximate, as everything had to be adjusted periodically to keep the discharge from either going out, or the power supply drawing too much current and shutting off. We did do a 5 hour test on the bubble detector without running the fusor and did not see a thing, so we are confident we got at least something.

With that said, Adam and I feel that the project can finally be called a success, as Adam can now use this as a demonstration tool in classes, showing students that this is a machine that can actually fuse the atom. (The fusor will almost always be run in a lower-voltage demo mode, but the idea is that it looks similar, and has done fusion in the past) We recently showed the fusor to Professor Ingebretsen's class, (He was the one who helped get everything started on this project) and was pretty well received by his students. If all goes right, this machine will be available to show physics students at the U of U real, actual fusion for some time to come. A big thank you to everyone who offered advice and support on these forums.

On to the pictures:

#1 New bell jar and grids

#2 Fusor w/ power supply

#3 Star mode

#4 Star mode 2

#5 Star mode 3

#6 Bubbles!
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Star mode.jpg
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Carl Willis
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Re: Archived - University of Utah's new demo fusor - we have fusion!

Post by Carl Willis »

Chris,

Nice work and a great report. Nothing like a bell jar for showing off the beautiful red star discharge in deuterium! Welcome to the Neutron Club.

-Carl
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Doug Coulter
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Re: Archived - University of Utah's new demo fusor - we have fusion!

Post by Doug Coulter »

Good show all around! Very pretty as well.

We find we only start seeing some neutrons (out of the noise) right around the volts you are using, and that it gets better fast (and the X rays worse) as volts go up and pressure goes down to compensate and keep the current reasonable, up to our limit of 53 kv or so. Here we handled the X rays by shielding the bulk of the tank with lead, and getting a couple of good, thick pieces of lead glass for the viewports so we could still see the pretty stuff. We have definitely found it of value to be able to see this from more than one angle here too.

The good old eyeballs blow any webcam away -- stereo vision, color fidelity, all that, but you have to stay alive to enjoy it.

I'd sure get rid of silver solder if I could. Although our inner grid does glow, our tank walls get most of the watts of heat, spread out more, of course. You're probably running near the limits now. Of course, we all hope you used Cd free silver solder....

I finally gave in to worry and made an exhaust for my vacuum system that goes outdoors...
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Richard Hull
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Re: Archived - University of Utah's new demo fusor - we have fusion!

Post by Richard Hull »

Chris,

A great show there and you are the first I am aware of to do the rather dangerous fusion in a bell jar. While the output was low, your 5 hour, no gas run proved to limped across the fusion line.

I will add your name to the neutron club.

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
Chris Roberts
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Re: Archived - University of Utah's new demo fusor - we have fusion!

Post by Chris Roberts »

Awesome, thank you very much Richard. I would like to ask if it is ok that Adam Beehler's name be added as well, as it technically is his fusor, and he was an equal on this project with me.

Thanks again, I am really excited and honored to be part of the club now.

-Chris
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