Matt Gibson Fusor

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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

You have done a great job on removing the deposition products. It is about as clear as it will get. The brown-purple tint is solarization of the glass and is there pretty much forever. It is caused by penetrating radiation, in this case x-rays and absorption of "vacuum UV" created while running the fusor over time.

This is a long known and studied process and is due to various tramp inclusion in glass manufacture. Manganese, titanium, arsenic, and antimony creeping into the glass mix is considered one of many elements and compounds that contribute to this malady. I have several old, used x-ray tubes and all have this brown solarization with a tendency in some to even be a pure purple solarization. Again, this depends on tramp clear chemical inclusions becoming colored under short wave radiation bombardment over time.

I have cleaned ports for years and this is the very best you can do.

There are a number of scholarly papers written on this phenomenon.

http://maajournal.com/Issues/2009/FullTextAbdAllah.pdf

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: Matt Gibson Fusor

Post by Matt_Gibson »

At least they are easy to clean up…

I’ve found another issue. I seem to have a really bad leak: I’m up over 2.5 torr in less than 24 hours. I began isolating every section by moving my gauge around. I wound up all the way down to the main pump and figured it must be the gauge itself. I swapped it out for another gauge, put everything back together, and found the same leak rate.

So now I’m wondering if something made it’s way in during all of my swapping around with the cube that could be outgassing this bad instead?

-Matt
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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

I wouldn't call that a bad leak - also, since you likely opened your system to swap the gauge around, you most likely added water vapor. Its possible that is just out gassing. Time will certainly tell - out gassing will decrease in time as you keep the system closed and pumped.
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

I guess I’m just used to only going up 30-40 microns after 24 hours then…I’ll try doing some heating runs once I’ve got my doodads switched over to swagelok.

How does leaking and outgassing affect wall loading? I know that letting the system reach atmospheric pressure pretty much requires you to start over again…

-Matt
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

I, long ago, gave up on leaks in fusor IV after it proved itself a good performer in the 1million neuts/sec mark. Its average leak rate after the end of a run, sealed- off, while still hot was 1 micron every 90 seconds!! For the picky vacuumist this is untenable! However, I proved it is not a big deal for 17 years. The diff pump could still take the system in the 10e-4 torr range and that was good enough to admit D2. If you have a good turbo or diff pump that can do this, then you are fine.

I figure it was my welds but I used up and breathed in over what seemed like a gallon of acetone vapor! Over the years, I would get a "wild hair" and hunt for the leak again and again, but zip...... Just a lot of vapor to the lungs.

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: Matt Gibson Fusor

Post by Matt_Gibson »

My turbo rips it down from 20 microns to 0.01 microns before it even hits 50% speed, so this “leak” isn’t affecting things from that end…I may even enable to the 66% mode to lessen wear/tear and shorten the spin down time.

I’m just concerned over losing any loading, but it doesn’t seem to be a problem?

-Matt
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

To avoid hi-jacking this thread about Matt's fusor, I moved my reply originally posted here to a separate thread related to my issues with leaks and pump down rates in answer to Matt's posting above.........

viewtopic.php?t=14499

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: Matt Gibson Fusor

Post by Matt_Gibson »

Minor update:

Swapped out my vcr4 to kf25 adapter on MFC to a swagelok fitting. I’m now able to pull the d2 line down to .01microns when I plug the polyethylene tubing, in just a minute or so. With my gas syringe, I can get down close to 1 micron. This is a huge improvement! So, swagelok from here on out…

Also, I’ve noticed that my “leak” rate is back to around 0.15 microns per minute…

As for my psu upgrade (driver portion) I’ve got a cm300dy half bridge IGBT module coming. I plan to use some gate driver ICs to drive it (via gdt) directly from my signal generator. Seems like major overkill, but it was cheap ($60) and I like overkill. Hopefully this lets me push my run times way beyond what my car amp can do and at much higher frequency (35khz vs 18khz).

-Matt
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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

Maybe a leak but more likely just typical out gassing. For instance, my system after pumping for two days took 90 minutes to reach 110 microns; however, after 24 hours it only rose to just 350 microns (after a few days, still only a few torr.) This is what out gassing does - it can be somewhat rapid at first after closing the system off (for a fairly clean system) but rapidly slows as the pressure rises.
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Outgassing makes sense. If I close down the pumps while the chamber is hot, I’ll see pressure rise much faster than if I leave the pumps running while it cools off.

Evacuating the deuterium feed line and the MFC before operation seems to have tremendously boosted operation. I am now able to go from start to full blast in just a few seconds. I am also able to go much longer before my car amp overheats…

Btw- I enabled the turbo standby mode (66% speed) and it worked very well, so I’ll leave it like that.

-Matt
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

You are finding or have found your niche of operation. It takes time and relates to my recent FAQ on operation. It is an art that is homed in on by understanding all the sciences and technologies of the fusor system. Yes, the fusor might be a "stupid simple device" so far as doing fusion is concerned. However, this very simplicity and its operation on a razor thin edge between glow mode and total arc-over conditions, requires a lot of finesse and artistic skills. The science and technology of the device is a must to understand before you can do the art work to make it go and do fusion really well.

It all seems so easy and natural, once you get there. The win is not the fusion. The win is the knowledge and understanding obtained over the entire process. Sadly or blessedly, (your choice), once you have done amateur fusion really well, no one will ever be able to "pull the wool" over your eyes related to nuclear fusion, regardless of your take on its future in our lives.

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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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

Good idea on the turbo - if reduced speed works it certainly extends the life of the pump. This also indicates your system really does not have any significant leaks.
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

So I’m trying to figure out if I’ve exceeded the mega neutron mark yet. So far, there hasn’t been alot of work done with the Ludlum Priscilla probes that everyone jumped on last year. This is what I’ve been using for my neutron detection.

My best results to date:

Setup: Ludlum Priscilla probe face placed 32cm from center of fusor. Neutron oven placed 8cm from center of fusor.

13 microns, 57kV, 10mA, 4 minutes. I averaged around 7mR/hr with quite a few moves into the 8mR/hr range and a brief 9+mR/hr hit.

Silver activated to 11,000cpm on my Ludlum 44-9 probe.

Going by Ludlum’s figures, that 9mR/hr hit translates into 3150cpm. I believe a TIER number would then be 3150*12861 = 675,226n/s. Seems low to me for pushing up towards 600w into the fusor and seeing 11,000cpm silver activation.

-Matt
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Re: Matt Gibson Fusor

Post by Jim Kovalchick »

Matt,
I find it very likely that you passed the mega mark multiple times over at that voltage, current, and silver activation level.

You should able to activate some other elements too.

Nice work,

Jim K
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Re: Matt Gibson Fusor

Post by Jim Kovalchick »

How is the Ludlum giving dose rate? Is it based on thermal neutrons or is it corrected for energy?
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

What I know is that it detects fast neutrons. What it does after that, I don’t know…Above my current level of understanding :-)

Ideally, we would have a correction factor based off a bubble detector or other known detector.

I know that we probably bought the majority of these Ludlums, come on guys!

-Matt
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Re: Matt Gibson Fusor

Post by Jim Kovalchick »

Dose rate in rem/hr should equate to a neutron flux that is a radiation protection standard independent of the detector assuming it is properly calibrated. There is also a difference in quality factor depending on the neutron energy.

In general one can assume that a fluence of 25 million neutrons need to come through a cm² to equate to a rem. Assuming 8 mrem/hr at 32 cm away, that equates to about 715,000 neutrons a second by my calculation.
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Re: Matt Gibson Fusor

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I am sure that you have exceeded the mega mark. Remember, if you are not near a beam impact on the fusor with a spherical grid, (multi-beaming), you are not getting a strong fluence as non-beam points would be more isotropic velocity space fusion which we more or less know that is not the ideal point. We live, and do, and we learn.

A large moderator on activation efforts will tend to intercept, collect and make use of more fast neutrons to thermalize and, thereby, activate.

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: Matt Gibson Fusor

Post by Matt_Gibson »

I should be inline with a beam impact point, but should try moving the probe around a bit to see how things are affected. Looks like I have an experiment to do, after work!

-Matt
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Re: Matt Gibson Fusor

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A cube has two beams to split the energy of fusion into with only moderate velocity space fusion around it. The sphere or cylinder of some size with a spherical grid has many beam points to split the energy up into. These latter fusors need a huge moderator for both detection and activation.

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: Matt Gibson Fusor

Post by Matt_Gibson »

Got ahold of a bubble detector (23b/mR) thanks to Anze. Did a few runs today, the best one:

Using my new transformer with my 6 stage CW full wave multiplier:

66kV and 10mA at 11.66microns. Bubble detector is 35cm from the chamber center. I got 18 bubbles in 60 seconds. My Ludlum PRESCILA probe was averaging 105mR/hr at 7.6cm from chamber center.

The BTI bubble detector calculator is giving me 5.6E6 n/s! Looks like I’m well beyond the mega mark now. My multiplier should be good for 72kV but I’m hearing popping coming from it at 66kV :-(

Here’s a picture of the bubble detector. A few bubbles are on the other side and not in the photo.
CB9E5423-3CCF-47A5-B307-9A3F787FF636.jpeg

-Matt
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Finn Hammer
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Re: Matt Gibson Fusor

Post by Finn Hammer »

Matt,
Congratulations. The mega mark is a legendary acheivement, and one that can be reached with relative ease. Just build a high multiplier, and the road is paved.
Building your own multiplier is a very powerfull activity, because it brings about, virtually unlimited voltage.
The next step could be to increase pressure, and hope the grid will sustain the increase in current. You will see E+7 before christmas.

Cheers, Finn Hammer
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Thanks Finn! I was thinking about adding some water cooling blocks to my cube that I put together, but I might just see how hard I can push this one for awhile…Maybe I can hit E7 without having to go the cube route?

Any ideas as to what I’m hearing from my multiplier? Is it popping noises from capacitor punch through? Maybe arcing within the oil?

-Matt
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Re: Matt Gibson Fusor

Post by Finn Hammer »

Popping: perhaps this, maby that. My input would be pure guessing. Here is how I suggest you can find out yourself.
If you have arching under oil, it can best be viewed in total darkness, after your eyes have adjusted. That takes about 5 minutes.
Popping internally really can't be detected without a destructive examination, where you force access to the roll of dielectric/electrode inside the cap package.
Unrolling the plastic foil will reveal big blotches of evaporated electrode material on the foils, if the pops are due to internal punctures of the dielectric, with the associated self healing.
This is sommething that happens if you over volt the caps. You cannot overcurrent the caps in this kind of applicarion.
If you want to walk the bleeding edge of high voltage capacitor application, you have to be prepared to perform these autopsies.

Cheers, Finn Hammer
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

I notice that voltage drops a few kV during the popping. Definitely seems like the capacitors are seeing internal arcs. They are rated for 6kV each and I use two in series for 12kV. This ought to be good for 72kV for the total multiplier, so I’m disappointed to see this sort of thing happening in the 60kV range.

One other odd observation is that it used to do this in the 50kV range. After some popping, it can get up to the 60kV range without popping. It’s almost as if it’s breaking itself in or something.

It’s in an opaque container so I can’t see any flashes. If I have a major failure I’ll definitely do some post operation on it to see what’s happening.

-Matt
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