Jim Kovalchick -My attempt at smaller fusor

[Frank Sanns]

Part of the issue that I have with this thread has nothing to do with your work Jim. It is the fact that Richard and I have not moderated it so that the technical discussions occur elsewhere on the forum rather than in your showcase thread. This is YOUR images thread and as such the rest of us should take the technical into another thread. Only complements or minor commentary should be going on in this section by others. Going round and round on the details of fusion in general are not critiques of your work but rather discussions outside of your work but trigger by your work. That did not come out right but you get the idea.

I looked back through it and I do not see a good way to relocated the discussions without destroying your thread, which we will not do. The problem is that discussions on the matter seem to be directed at you are they are not. They are good technical questions, suppositions, and answers for a stand alone post. Appearing in your showcase though feels personal to you as I saw earlier today. I think a new generic technical discussion on such matter is warranted.

The other problem is that historically, the Images section gets thinned and deleted except for the very best. You of course have nothing to worry about there but in the future, Richard and I need to catch this sooner. Again, my bad.

[Richard Hull]

Like I noted, I leave this field and its associated problems as an activity for the advancing student. I am a neutron guy, not a fusion guy. I have to work with fusion to get my neutrons.

The cross has 6 arms welded at sharp right angles at less than one inch from the grid. You can't radius these weldments to a level suitable in a common 1.5 inch cross without risking cutting into the weld so deep as to damage the cross. I see no sparkling at the weldments which had no little beads, etc. (smooth).

In my perpetually vigilant video image sprayed over a 9"X 9" Monitor screen there is no warning, no creeping currents, just instant unpredictable white arcs. These tight little cross systems are RF and EMI nighthmares! Subtle tritchel pulses aplenty to add to the RF mayhem. I would be highly suspect of any electronic neutron counting around them. This is from several hundred of times I spent hitting the reset button on the counter.

My actual grid diameter in the direction of the discharge streams is .40 inch and was originally a .501 sphere. Enjoy the hunt gentlemen. I need neutrons and neutrons alone. Cylinders and spheres, cylinders and spheres.

Like Frank, this is nothing to do with Jim's effort. I learned much of what I know of value prior to my beginning this cross work in this thread solely from Jim and a few others. Jon R. is always a special case for successes. This is why I leave all this work to the other gentlemen here who will persist in this effort. I had fun and burned off over 40 hours mostly from 11PM at night until stumbling into bed about 8 AM in the morning. Awaking at 4 PM in time for my 1 mile walk, supper, some time with the wife and back at it again. All the time, looking for a sweet spot that never came due to arcs. I went through 8 conflat copper gaskets removing and replacing the grid system and HV insulator that took 44kv on fusor IV I have a robust system. All of my efforts came to naught. (polishing, rounding, careful alignment, etc.) The big x-ray power supply and turbo controller really took some nasty belts on the chin and got up off the canvas to start over again. As the owner of this less than a champ, I now throw in the towel. This system will sit as a trophy until I decide to move on the newer fusor V as this was a non-fusing system in my view, but a winner for any DIY newbie.

Richard Hull

[Dennis P Brown]

Hello and glad you posted your results on your fusor. Your work has been excellent.
I apologize if you think I am "casting stones". I did not intend this. I too built such a small volume device (though, didn't have the success you achieved.)
Again, your experimental work is very good and do stay at it and continue to post - small volume fusors are and remain an interesting project for people building fusors (as I pointed out, they offer superior performance for smaller power supplies.)

[Jim Kovalchick]

To investigate my diminishing neutron numbers I opened my chamber last night. I found no discernable issues with the inner surfaces. I do not have an endoscope camera, and not wanting to open my beam end conflats, I did not exam those surfaces. The stainless steel grid looked better than I thought. No signs of melting. The outside of the grid tube was tarnished with a shiny pale blue. I wish I could get a good picture of this, but the inner surface of the grid tube was a dull light gray. I can't make any specific conclusions from these observations.

I elected to put the fusor back together with a new grid. I dont have a tungsten tube to try yet, so I decided to return to using titanium. My first grid was a poorly formed demo tube of Ti. This time I formed and polished a short tube of Ti sheet. I recycled my titanium clip from the latest grid. I decided to make the grid a little shorter than my last one to give more margin to arc shorting. The tube is also wider to more closely match the bigger diameter of other small fusors on this forum. I forgot to take exact measurements of the grid before sealing the chamber, but the opening is about .75 inches. I put a slight bend in my stem to compensate for sag to center the grid in the chamber. The attached photo is my new grid before placing it in the chamber.
In the coming days, I expect to test the new grid. I will continue to post results here.
Jim K

[Jim Kovalchick]

I walked the new grid up to - 38 kV and 5 mA with almost no difficulty. Some sparkles now and then, but that subsided quickly. I kept my current at 5 mA or below.

Obviously my grid is heating unevenly, and my guess is that is related to my grid clamp. The beam also looks a little feathery, but I'm not sure if that is significant.

Initial neutron numbers at 38 kV were more than twice what I recorded yesterday for the same conditions. 559 counts in one minute on a beam end of the cross using an Eberline PNC tube that read 400 cpm when held against the shell of Richard's fusor IV. From here, I would like to see if these numbers change with successive runs.

[Jim Kovalchick]

You guys are probably tired of hearing about iterations of my grid, but here is the latest. I have added some bulk to it to try to time extend the heat driven window to H desorption. My stainless grid would get yellow hot quickly with any real current. My titanium grid was thin and heated unevenly. My goal is maximizing neutrons for my top end voltage of 40 kV by driving current. I hope to try this new one in the next couple days.

Tungsten carbide. 12 mm tall, 17 mm inner diameter, 22 mm outer diameter. Definitely my heaviest grid in this fusor and hightest melting point.

[Jim Kovalchick]

Tungsten carbide grid
I walked up voltage on the new grid to -37 kV with no difficulty. There was a little cleaning sparks but not much to speak of.

I did manage to make the grid glow red, but it took a long time to do it at 6 mA. No really bad colors like yellow. Also heating looks even.

Neutron numbers were about as good as I've seen on this fusor, and I did not go to 40 kV.

The real test will be going to top voltage quickly after the chamber is conditioned and see what the numbers look like then.

[Richard Hull]

Great work Jim, I have secretly, and without comment, also changed my grid to a custom made machined titanium cylinder and done very limited fusion with it. (just under 100k n/sec) before the *%$@#! thing arced shutting down the Turbo. I remain very frustrated with the entire cross system, and shall still rip this thing apart, ultimately. I just feel that the tolerances are just too close due to the grid/stalk positions relative to the 6 sharp right angle weldments of the arms. If a 4" six way cross was not so expensive, that might be the way to go, but the smooth warranted spherical system is a proven performer.

I will continue what effort I can with this system until it so frustrates me that without a care, at that point, I will gleefully tear it to pieces. The work is so pathetic that I just haven't the heart to report on it. It is a beautiful system in looks and operation if you like sudden arc breakdowns about the time you think you are getting there through careful operation and a couple of hours of tedious nursing. Yes, it is an easy win for newbies who just want a win and then leave, but for a seasoned veteran attempting to equal and better his previous work it is a study in frustration.

Richard Hull

[Jim Kovalchick]

Richard,
I too am frustrated, but I remain inspired by Jon Rosenstiel. I am starting to believe though that the man is some kind of wizard.
Regarding the sparks, I have found that the dimensions of the grid are very important that way, but more importantly, I can't rely on glow cleaning to get rid of my sins. I suspect your construction techniques are better than mine, and you have less sparking. I find that as voltage goes up, the glow cleaning sparks are what initiate the nasty arcs. Yesterday, I had to slow down at 37 kV because my grid clamp started sparking too much for my liking, and I suspected I was close to striking a continuous arc. I am going to try baking longer at lower voltages, and I'm confident I will be able to get to stable 40 kV ops.
My new grid was intended to get somewhat close to Jon's dimensions at least in diameter. I also wanted some mass to give it some heat capacity, a high melting point, and a ultra smooth finish. I'm not sure of the overall impact of it, but to me, I think a higher desorption temperature would be advantageous. Picking tungsten carbide gets me closer to my goal. I certainly can't sinter my own WC grid, but why bother, when they sell wedding rings in various sizes for a little over 15 bucks polished? This grid is a size 7 lol.
My neutrons seem to plateau as things heat up. My next goal is to figure out if the culprit is grid heating or chamber heating. I am working on some ideas for figuring it out that involve operations and construction.
More to come.
Jim K

[Dennis P Brown]

First, very good work on your fusor, Jim. Sorry to hear, Richard but the issues with 'real' small fusors, apparently, can be difficult but that has made Jim's work both rather original and interesting.

This work by Jim makes me think I should re-explore creating a small fusor via my first and rather successful method - using a large fusor but with a small "anode cage".

But that fusor project will have to wait till I build a new building to house my next generation equipment (I also have a lot of research equipment for making my new armor that is based on my revolutionary composite that is a flexible glass.) That equipment, along with the fusor, has my garage filled so I have no room for my car - lol.

I gave up on working on fusors in my Den due to safety issues since that is just too small/restrictive an area. A few months ago I laid out, dug and built the foundation of the new facility but thanks to the virus, have been forced to put that build on hold - also, I've rebuilt many parts of my existing dwelling - apparently, my endurance isn't what it use to be - .

[Jim Kovalchick]

Dennis,
Wouldn't the small anode cage still create close tolerances that would create the chance of the arc phenomenon Richard and I are experiencing?

Jim K

[Richard Hull]

Jim do not think Jon is a wizard, remember, his is not a cross but a 4" square block into which I am sure he bored the largest hole that could mount his conflats. Even a tiny amount over the 1.5" tubulation arms found in our crosses could help avoid arcing and I wonder if Jon rounded his internal hole joint right angles; something which we cannot do. He is such a damned good machinist and has enough long held fusion savvy to consider this 'radiusing" a real aid in avoiding arcs at high voltages in close quarters. However, if he drilled 1.5 inch holes and left them razor sharp then I might agree, He is a wizard. I might have guessed this before leaping into this current effort. But, like I say, I will piddle with this pig until either I or it squeals "uncle".... and I am close to squealing.

Regarding your issues and mine.... I think it is a matter of cathode heating and electron emissive runaway and thereby, conduction, within close toleranced, non-radiused edges, of the arms of the cross. I can't imagine the chamber heating to above 250 degrees F or even higher playing any sort of role in this mutual nightmare. We are guys who have been there and done that in the mega neutron range. We are also fully aware of conditioning issues and the slow and tedious operator learning curve for any fusor and are more than willing to inch the thing forward in real baby steps. We are not looking for the quick win like a newbie. We have both poured a number of hours into our systems. The frustration is real and palpable.

It is now past my normal bed time, so I will get some shut-eye.

Richard Hull

[Dennis P Brown]

As for maybe the same arc issues - that might or might not be the case if I continue to shrink my anode: while it would seem likely if I continued along that path, my results didn't appear to require that to achieve the same pressure increase as seen in small fusors. My anode cage was much larger than a 50 mm cross. What I was interested in was operating at the same pressure as most such small, 50 mm devices - which I did. Further, since the cage was still rather large (about 200 mm diameter, 500 mm vertical) my cathode was also rather large. In fact, it was my orginal cathode. As a result, it was well worn already (no sharp points and somewhat erroded.)

For me, the operating pressure was the key parameter I was testing and had suspected was the real advantage offered by small fusors. That I achievied typical 50 mm cross fusor pressures was what I had hoped - so, maybe the constraits on this approch - large fusor volume but somewhat smaller anode walls in a cage form are more relaxed. That I had a 50% increase in neutron count compared to my orginal large fusor flux was a significant improvement well worth the effort- so, except for the anode cage and steady operating pressure all else was the same (cathode size, total volume, power supply/voltage/current.) Getting the system to operate at far higher pressure was my goal. This experiment proved that volume itself wasn't either the issue or constraight on higher pressure systems/better neutron count for the same power but rather, simply available fuel.

All this is not in any way to indicate that making smaller fusors isn't both a worth while expeiment or a more cost effective approch. Again, your posts are very useful and experiments are very good work. Keep up experimenting - it opens up the parameter space for fusors and is, in my opinion, something that makes the science more accessible.

[Jim Kovalchick]

I did some more conditioning today. 38 kV at 7.8mA. My neutron count rate at one of my beam ends was 1.75 times the count rate the same detector read held to the shell of Richard's Fusor IV. I need to get a good silver foil to see what kind of activation I can get. Anyone know of a cheap place to get a 2 inch diameter .007 foil?

At this upper end I am getting arcs at my external feedthrough connection. I have it wrapped with kapton, but I must be at the top end of that.

I used the opportunity to dig one of my standby neutron detectors out of storage and try it out.

This one is an Ebrrline HP-280 epithermal ball. It doesn't work for the fusor, but if I put my hand over the ball, I was able to get some counts put of it.

The ball is cadmium lined to kill thermal neutrons, so putting some moderator between it and the neutron source only would work if I under-moderate. I took the little Nancy Wood BF3 detector out of the ball and put it in the detector well in the parafin block of my old PNC. At 1700 V bias, it gave 400 cpm when the PNC read 700 cpm. The count rate was a little jump though. I may need to fiddle with the bias and threshold some more. Either way. It's nice to know this old dumpster save works.

Jim K

[Frank Sanns]

Nice work Jim.

My only comment to you and Richard again is symmetry. This configuration is VERY critical for beam paths. The proof of this is in your own photos with the feathered beam on one side and a better formed one on the other side.

When I was out at Jon Rosenstiel's this past January, I had a chance to see his precision in his alignment and his geometry. I also had the chance to see the actual Philo Farnsworth grids and configurations. There are similar trends. Symmetry is king, ratios of inner grid sizes and placements, and also one other important but not so obvious to a lay person (no suggesting that of you), is the detrimental roll of ion funneling with conical inner grids.

I am NOT trying to insult anybody. Please take it as it is given since I have had eyes on these devices and seen results. Of course I have done many variations too but that just is icing.

[Jim Kovalchick]

Frank,
Yes. I agree there are issues with symmetry. I am working on plans to resolve symmetry issues during my next chamber opening. I rushed this installation to test the grid. I have been making plans for stiffening my stem and tweaking my coupling and grid clip.

My upper beam has feathery through several different grids. I plan to examine past pictures to find the common theme.

When I do all this I also will try to make my feedthrough take a few more kV.

[Jon Rosenstiel]

Richard mentioned cube vs. cross internal dimensions. My cube’s bore is 1.875” in diameter. (BTW, are you guys using KF-40 or KF-50 crosses?) I lightly broke/rounded off the sharp edges where the hv feedthrough/viewport/vacuum port bores meet the main bore. I took a look at some KF-25 fittings I have (a couple of tees and a cross) and they are all different internally. One had really sharp edges, another had a nice smooth radius and the third was somewhere in-between the two extremes.

My first cathode had an OD of 1”, and my present one has an OD of 0.75”. Neither had issues with arcing to the chamber walls, and I’ve run them both up to 70 kV on occasion. But I have lost two 30 kV rated feedthroughs to vacuum side puncturing. (Ouch!) Seems as though one can easily oil insulate the air-side to hold off double or triple the feedthrough’s rated voltage, but unfortunately, that doesn’t work as well on the vacuum side.

The 1” OD cathode was a poor performer, about one-half the neutron output of my spherical fusor. When I changed to the 0.75” OD cathode the neutron numbers soared to almost double the output of my spherical fusor.
So it seems that cathode dimensions (mainly OD) and symmetry (as Frank mentioned) are super critical to good performance. And I suspect the magnets Joe Gayo uses may help symmetry, but I’ve not seen any improvement when I tried them. (Difference may be that Joe is running higher voltages than I am)

JonR

[Richard Hull]

I am using the stock 2.75 CF cross with a 1.44" inside bore and a .5" titanium cylinder cathode currently. I assume Jim is also using a 2.75 cross, as well. All arcs are internal, cathode to the sharp right angle join welds. Now that me turbo is blown up due to arcing. I doubt if I get it going again that I will ever fire up this iteration of fusor V ever again.

Richard Hull

[Jim Kovalchick]

As Richard stated, I am also using a 2.75 CF cross. I tried a couple things this evening. I fiddled quite a bit to get better symmetry. The beam quality is much better. Unfortunately I added some alumina to the rear of my stem and now I am getting lots of arcing. Two harbor freight meters died before I killed the power

[Richard Hull]

Note: the worst and most prevalent arcing in my system was when I Alumina shielded my grid stalk. I saw how thin Jim's stalk was and taking that cue, I noted that I could hit double the normal 12kv arcing voltage when I got rid of the 1/4" stalk with alumina and went to a naked 1/8" Ti rod to my new titanium cylinder grid. Just sayin'........

Richard

[Jim Kovalchick]

I got rid of the alumina. Unfortunately, the problem I added the alumina for in the first place is back. At 38 kV I am hearing nasty arcing back at the connection of my feedthrough. I may just be at it's limit.

More bad news: Better symmetry has bought me a prolonged occurence of an electron beam orthogonal to the axis of my grid openings directly at the center of my view port. I have seen this before but it only showed at much lower voltages and higher pressures. In the attached picture there is a small dot where the electrons are fluorescencing the glass. Note there are two spots in the picture. There is a smaller, well defined spot and a bigger more ghostly one near it. I am more afraid of the small one. The glass was hot to the touch but because I could keep my finger on it, I am guessing below 115 F on the outside. I held a strong magnet near the dot, and the dot does not move. The only effect of the magnet was some flickering of the lighter fluorescence across the face of the glass.

In better news: At 35 kV and 6.6 mA, before I hit the arc wall at 38 kV, I measured neutron numbers that I wont report yet because they startled me. I pulled the tube from the moderator to make sure I wasn't seeing noise, and watched my indications go nearly to bottom of scale. Suffice to say, if these numbers are real, the tweaking of my grid positioning made a big difference in the fusion rate, as several have predicted.

[Jon Rosenstiel]

I keep confusing CF with KF, sorry. So the 2.75” CF cross has an ID of 1.44”… wow, that’s pretty darn tight, makes for a real “high-tension” environment.

With my 6" spherical fusor the alumina tubes seemed to be a positive, not so with the cube.

JonR

[Richard Hull]

Have you recently checked the x-rays at that dot on the window at that voltage?

Richard Hull

[Jim Kovalchick]

The xrays at the window are not trivial. I limit my exposure with remote camera pics, distance, and a lead flap that usually hangs over the view port. I'm not sure I want to publish a number. My ion chamber is not calibrated and the desiccant is pink right now so it will significantly over report.
.
I'm not sure the xrays from the electron beam on the window will be as significant as those on the beam ends. The electron beam doesnt seem to be making near as much plasma because the beam is invisible other than the dot.
.
This evening I did another run in the low to mid 30 kV range. I stayed away from higher voltages, but I also found that st 35 kV I had to keep current low otherwise grid to wall arcs start. I think I found this fusor's upper range.
.
I also recorded a new personal high neutron count rate. Using rate indication only, not a scaler, the peak rate match the number from earlier today of 1200 cpm.
.
Next steps will be to establish stable operation standards including applying final shielding installation, operation duration limits, and a workable neutron oven.

[Frank Sanns]

Looks like you are make good progress Jim.

You won't see an electron beam in a Fusor. The pressure is too low. The mean free path is multiple km so there is no significant interaction of electrons with the plasma. As you have noted though, you will see the fluorescence of the electron beam impinging upon surfaces.

All of the visible plasma in the fusor is excited by ions and fast neutrals alone.