Fusor Forums

Today at the end of the day at work I’ve come to tension the drive belt in the vacuum pump of our demo fusor. I’ve started the machine, just to watch the plasma glow before I leave for home. As I’m currently involved in Thomson Spectrometer I started to think about a simple crossed fields attachment for fusor to analyze masses and charges of particles in the streamers. Quite meaninglessly I’ve picked up a weak magnet an applied it to the outer shell of the fusor, to see how the streamers will deflect. But something different happened.
The machine was operating at 1E-2hPa pressure range, 2,3kV and about 7mA. After putting the weak ceramic magnet on the shell the current doubled, causing the grid to glow on the magnet side. Close to the shell, in the strongest magnetic field area a new glow region formed.
The reason of of course quite obvious. The electrons flying towards the shell started to gyrate along field lines increasing the collision ratio, and thus the ionization. It’s the trick used in cold cathode ionization gauges. But why don’t use this trick in a fusor to improve ionization in the anode region? I wonder what effect it will have in a real, neutron producing machine?

Yes all of this was noted back in 1998. I show some of this effort in a photo below. Magnets near the shell, externally positioned, would really be a great ionizer system. This occasionally gets mentioned here.

Note the localized grid heating which might be an issue with strong magnetic fields forcing intense ionization and bombardment. Controllable electromagnets might be an idea.

Richard Hull

Hi:
Joe Gayo actually used an axial magnetic field in his superb work:

viewtopic.php?f=6&t=12826&p=83473#p83473

Re: Magnets in Joe Gayo's design.

Jon Rosenstiel's cube fusor is basically the same design and he has had direct contact and conversations with Joe. I had never heard anything about the effect from the magnets so I asked Jon about it in his thread in Nov.

viewtopic.php?f=6&t=12954&start=20#p84783

Seems putting a magnetic field through it did not help fusion numbers.
"Magnets: (Edited 11-10-19) Depending upon positioning, the magnets either did nothing or reduced neutron output."

That's interesting. It should be expected that at higher energies the effect is reduced due to the smaller gyration radius for the same magnetic field. However, in the original post Joe is working with 70kV, while Jon is using 40kV. How can its effect be more noticeable in the first case? Am I missing something here?

Joe joined the forum about a year ago and dived right in with his plans for a well thought out small fusor design. He very quickly built it and had success. Jon has followed up using a very similar design, starting about mid last year.

After Joe began to do fusion and shared his results over a few months, it seems he has mostly been inactive on the forum. Not saying he has stopped his fusion work; I don't know.

I know his initial plan was to have a magnetic field through the center axis of the cylindrical arrangement. When he was sharing results I don't recall any mention of the magnetic field. I think I asked him about it here and if he had any data with/without the magnets. I don't think I got a reply.

My extrapolated impression is that the magnetic field didn't seem to help in either effort but I don't know that for sure.

Maybe if Jon sees this he can comment with first hand knowledge.

At all events, work or not, improve or not, it is, blessedly, not an attempt at magnetic confinement!

Just for grins and googlers, I just might try to wind 4 whiffle ball-like small magnetic coils right at the juncture of the four arms of my cross and piddle with coil strengths and yield. If it doesn't work, no big deal.

I can see some sort of magnetic ionization at least boosting ion numbers. Whether it boosts fusion due to increased deuteron count.... Who knows? Seems a logical extension, but then doesn't so much in fusion seem logical and then fail miserably. I haven't even dismantled fusor IV in the lab, yet! Some fast or already setup guys may take my idea and run with it.

Any such nice quadrature variable field set up will require a beefy "amp" level supply as the number of amp turns in any coils is the magnetic field maker and controller. Ultimately this may also make significant demand on the HV current supply as well. Everything screws with everything else. (catch 22) The beauty of this concept is that you can be doing fusion with no mag field and then slowly inch up the mag field and observe not only the neutron count but the voltage and current of the HV supply. Do away with the permanent magnet idea and do some real qualitative and quantitative research.

The above effort demands rigidly controlled and accurate instrumentation, something so few here can manage or will ever have at hand. I am not saying that only the big or old boys here can play, but only the adroit, skilled and careful might bring off this ever so rather simple and incremental bit of true research.

Just remember, I started this idea for the magnetic quadrature cross in this post when the fusion goes over unity!!! Chuckle... Regardless, you can trust I will bring up the rear in my only good time, perhaps only after another or others have monkeyed with the concept. Drawings to follow.

Richard Hull

From my understanding the main purpose of the magnets was to help stability, I don't recall Joe saying anything (good or bad) about their effect on NPR. (Neutron Production Rate) My main interest is activation so maximum neutron flux at the sample is what I'm after. Stability was not an issue for me (possibly because I'm running at lower voltages than Joe?) and all the magnets did was to increase the distance between the source of the neutrons and whatever it is that I'm trying to activate.
I suspect that cathode design may have a lot to do with the effect of the magnets.

Jon Rosenstiel

I agree with Jon. I just posted by simplified diagram above. I have no idea if any thing will be noted of significance. If not, then as Jon suggests the grid might be piddled with to "wring" out the design. Another idea is tungsten needles in the arm's conflat surfaces for field emission and slide the coils to the conflat ends of the arms to boost ionization at the needles the arms for acceleration towards the grid. This cat ain't nearly skinned yet. I feel a whole new paradigm far beyond the simple cross concept awaits the bold person here.

Again it is all about experiment. Jon is the current leader with Jim Kovalchick in the running. We haven't heard from Joe on this or any facet of his work in a while. Thanks go to Maciek for getting this old horse back on its feet in light of the new cross fusors.

A similar diagram on this second concept to appear here. The needles in the blank offs would produce copious high-field emission electrons, the magnet field coils would boost and focus this work of making deuterons. The blanks should still load with fast deuterium neutrals. Note: At high HV power supply currents, over time, the needle points will either dull or form small ball points.

Finally a jab at the DIY crowd. To most of these folks this kind of work is just a needless "bridge too far". They have their boast, (That they are up to doing this)....... bluster, (ideas that go no where or that they can't or will not test).... or win (I did fusion, I did fusion!). For them, why expend the extra work, time and costs? They are gone.

Richard Hull

As the idea of the magnetically controlled ionization looks interesting to me I’ve started to think on setup to test it. I tried to find a way to fit it into our small demo fusor, but the space is to limited, and also because of the big observation window the electric field is very non uniform. So I finally come to a new system with a more spherical geometry.


As the small hemispheres are expensive and hard to buy I’ve decided to use two EN10253-4 end caps, wich are cheap and available. I want to use a solid sphere as the cathode (item 3) with four mesh windows and two small apertures for the ion “beam”. This will look a bit like original ITT cathodes, which is cool as I think even if it fails (and have to be replaced with another design). The magnetic field will be generated by two solenoids (item 4) connected to the KF16 flanges in line with the cathode apertures. The solenoids will be equipped with soft iron poles (item 6). For plasma observation there is a small viewport in line with the meshed windows in the cathode and the KF25 port for additional diagnostics. The lower NW100 flange is the connection for the PDO300 300l/s diffusion pump which I’ve currently up and running with control valves and vacuum gauges. There is of course the gas valve (item 116) for pressure control.
Currently I’m not planning to use deuterium just observe the plasma formation and measure voltages and currents with different magnetic field strengths, polarities and gas pressures.

Wow, I am really enthusiastic about your design. I bet it will work out OK. I'll also bet it will be a real performer if D2 ever finds its way inside.

All the best if this gets built. Keep us in the loop. In good hands, this should beat anything the Farnsworth team put together that used D-D fusion. Just the right amount of complexity that can be readily assembled by a focused amateur.

Richard Hull

Hotta's group in Japan did considerable study of this subject in a cylindrical fusor and reported their results at the US-Japan IEC Workshop in College Park, MD, in 2012. Unfortunately, the web site where the presentations at that meeting were posted has since been taken down. They used mutiple coils on the outside of their cylindrical anode chamber and tried various combinations of different current directions in the coils. Their best results yielded a threefold increase in neutron production with the added magnetic fields. Their conclusion was that adding magnetic field near the anode confined the electrons and hence electron impact ionization of deuterium to the area nearest the anode, which would yield the highest energy ions after acceleration toward the cathode. I'm not aware of a comparable study in a spherical fusor or one made from a cross, but this should certainly be a fruitful area to explore. If the Hotta group explanation of the effect is correct, one would want to concentrate the magnetic field to areas nearest the anode.

In my post in the past I noted the movable coils on the cross arms might be jammed against the anode ends of the arms.

Richard Hull

Richard Hull wrote: ↑Sat Mar 14, 2020 5:19 pm Wow, I am really enthusiastic about your design.

Richard, it’s very encouraging to hear it from you. I don’t have such high expectations for this design and will be happy if I can learn something new about ionization and ion circulation in the fusor. I’m going to order parts on monday (shells, inox sphere for cathode and laser cut blanks for flanges). Most of the fittings I’ve in hand, so I hope to have it assembled in two months.

I wish you well on this. I am lagging behind in getting my 6 way cross Fusor V up and running. I have some vacuum part on order now.

Richard Hull