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 » Thu Apr 23, 2020 11:25 am

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

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

Post by Richard Hull » Thu Apr 23, 2020 12:41 pm

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
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Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Dennis P Brown
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Dennis P Brown » Thu Apr 23, 2020 2:35 pm

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.

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

Post by Jim Kovalchick » Fri Apr 24, 2020 4:53 pm

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
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Frank Sanns » Fri Apr 24, 2020 5:38 pm

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.

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

Post by Jim Kovalchick » Fri Apr 24, 2020 5:57 pm

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.

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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jon Rosenstiel » Fri Apr 24, 2020 10:55 pm

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
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Richard Hull » Sat Apr 25, 2020 1:29 am

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
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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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

Post by Jim Kovalchick » Sat Apr 25, 2020 1:39 am

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
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Richard Hull » Sat Apr 25, 2020 5:20 am

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
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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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