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 » Sat Feb 01, 2020 1:52 am

Here is fusor 'outtake '. Arcing from my recent grid while it was conditioning.
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Jim Kovalchick
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Jim Kovalchick » Sat Mar 07, 2020 5:39 pm

I made a major discovery about why my fusor results were lack luster. A hot connection on my power supply was taking up a lot of the current flow. I corrected the connection and now getting lots of neutrons and my grid heats to red at 6 mA. I did not discover this issue before because I measure my current at my XRT. This picture was taken at 28 kV and 6 mA. Not that I'm happy to see it glow red, but this is more like I expected before. If you zoom in, my phone's picture is very speckled.
Jim K
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Richard Hull
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Re: Jim Kovalchick -My attempt at smaller fusor

Post by Richard Hull » Sat Mar 07, 2020 6:35 pm

Nice picture! I like the red glow. Looks like real power is expended, but that is what fusors do. Too many want power out, but that is not what happens.
I hope to have fusor V on line this spring. I have some ideas that might, just, with some luck, amount to nothing.

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

Post by Mark Rowley » Sat Mar 07, 2020 6:54 pm

Nice to see it cranking out some good results and am looking forward to seeing your neutron counts.

Fwiw, that's close to the same input numbers I've attained with the 60kV precip supply.

Mark Rowley

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

Post by Jim Kovalchick » Mon Mar 09, 2020 5:59 pm

An update and a problem.
Update: At 40 kV and 5 mA I am getting roughly 1 million neutrons per second at one end of my cross. Definitely seems neutron readings are stronger at the ends of the electron beams.

Problem: Not a new issue, but as I encounter new voltages, there is initially some arcing until it cleans. With higher voltages, the transients on the system have become more severe. I have fried a couple harbor freight meters and a vacuum gage controller. I also noticed some arcing between hv connections and the shield ends pulled 8 inches back on the ends of the xray cable I am using. I read a paper last night warning about ungrounded ends of shields on xray cables especially where the cable long and coiled. Because xray cable is precious I had been reluctant to cut it. Today I cut 25 feet off it, used only the length I needed, and grounded both ends of the shield pulled 8 inches back from the ends. I did a run in this configuration and found that the few arcs inside the chamber caused less audible noise and my meters recovered quickly until one last arc killed another harbor freight meter. I have this one looking at current by looking at the drop across a 10 ohm power resistor in line with the ground from my XRT. This spot has killed three meters so far. I'm not sure what else I can do.

My power supply is a beefy XRT with a ballast resistor but no cap. The xray cable goes to a voltage divider bucket and then right to my feed through. My terminations are wrapped tight with multiple layers of kapton. I get a slight hiss at the end of the ballast resistor connection at 40 kV but no snapping. My transients start as just grid cleaning arcs that sometimes turn into transients.

My chamber is grounded into a star point which then terminates into a wall box copper ground.

Any ideas are welcome.

Jim K

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

Post by Bob Reite » Mon Mar 09, 2020 7:30 pm

The 10 ohm current sample resistor is a nasty point for transients. During an arcing event, that point tries to go to a very high reverse voltage. I lost a digital meter there. After that I installed 10 K series resistor in the ungrounded side going to the DMM, then put a 10 volt TVS diode across the meter connection. I had the TVS diodes on hand, as I use them for a similar purpose in vacuum tube transmitters at the cathode current sample. After doing that, the meter would still sometimes get "goofy" but at least it wasn't destroyed, power cycling the meter would bring it back.

If you can't get TVS diodes readily you can make two pairs of silicon diode strings. Figure out the maximum normal voltage you expect to read, then divide by 0.6 to get the number of diodes you will need. Hook the two stings in parallel back to back, this will give protection for a transient going either direction.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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

Post by Jim Kovalchick » Mon Mar 09, 2020 9:07 pm

Bob,
Thanks for the suggestion. A little arcing is to be expected so a circuit that is more tolerant is a better approach.
Jim K

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

Post by Jim Kovalchick » Wed Mar 11, 2020 2:00 pm

Bob,
I'm assuming a bidirectional tvs diode would eliminate the need for two diodes across my resistor. Is this correct?
I also wonder if the breakdown voltage value of the tvs is that important in an order of magnitude or so because I expect that surges of concern will produce higher voltages very fast and the tvs will react quickly.
Jim K

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

Post by Bob Reite » Fri Mar 13, 2020 6:55 pm

Yes. a bidirectional tvs does eliminate the need for two devices. I would choose a breakdown value about twice the highest voltage you expect to read under normal conditions.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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

Post by Jim Kovalchick » Wed Apr 08, 2020 11:32 pm

My neutron numbers have been dropping steadily over the last several runs. Today I took a series of measurements at various voltages from 30 to 40 kV with constant current. After I was done I went back to my starting voltage and repeated the measurement. The difference was huge. At -30 kV, 5 mA, and a starting beam end chamber chamber shell temperature of 88.9 degrees, the BF3 tube saw 230 counts in a minute. Same voltage and current, but starting temp of 150 degrees, the counts in one minute were down to 140.

Even my initial numbers today were half what they were a week ago. I suspect my grid and/or chamber must have experienced some changes. Perhaps I have driven my stainless steel grid to temperatures that caused accelerated plate out that is reducing absorption of deuterium in the chamber. I think it's time to open it up.
Jim K

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