Nathan Marshall - Fusor Progress

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
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Nathan Marshall
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Real name: Nathan Marshall
Location: Hutchinson, KS

Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Tue Apr 21, 2020 6:39 pm

Hello Mark,

Thank you! The inner grid is about 1.25” in diameter and the chamber is a 6” conflat cylinder, so it’s inner diameter is about 4”.

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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Mon Apr 27, 2020 8:49 pm

I finished building a ~30kv high voltage power supply, and I got it in an enclosure with oil yesterday. The high voltage is supplied by a very large flyback-style transformer with a huge secondary winding and a roomy air gap space between the primary and secondary. The primary is wound with 12 gauge solid copper wire. The output is fed into a full wave voltage tripler made with 30kv 820pf doorknob capacitors and 30kv 100ma diodes. The output is taken from the enclosure using 40kv wire. The output also goes to four 100 megohm MOX resistors under oil for voltage measurement. The output of these resistors is fed through a 100 uA meter, giving me a maximum voltage measurement of 40kv. The primary of the flyback is fed with a cheap "1000 W" eBay ZVS driver (I don't believe this purported power rating, but I won't be coming anywhere near this level of power). The DC power for the ZVS driver comes from two 15V power transformers in series, rectified with a beefy bridge rectifier and smoothed with a large capacitor. Using a variac, this gives me a heavy-duty variable 0-35 VDC supply for the ZVS driver. Some initial testing last night with just my mechanical pump running showed a current just over 60ua on the meter, or ~25kv. X-rays were pouring out of the viewport. I wear a lead radiology apron as a precaution to keep the rads off my nads, but where I was standing there was little to no radiation above background. I just put a 10 ohm 20 watt resistor from the fusor shell to the supply so I'll try to get a current measurement later today. I plan on making a nice enclosure for all the power circuitry soon.

I rigged up a Raspberry Pi single board computer with a cheap $15 arducam camera. After some fiddling, I got things to the point where I can remotely desktop into the RPi with my laptop and view what the camera sees through WiFi. This allows me to view the fusor grid from anywhere and with no wired connection to the camera.
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Mark Rowley
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Re: Nathan Marshall - Fusor Progress

Post by Mark Rowley » Mon Apr 27, 2020 10:33 pm

Excellent work Nathan. I'm hoping for the best possible results as this hobby in particular needs to get past the perception of reliance on ultra costly or impossible to locate power supplies.

Mark Rowley

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Richard Hull
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Re: Nathan Marshall - Fusor Progress

Post by Richard Hull » Mon Apr 27, 2020 11:07 pm

Nathan, You are admitted to the Plasma club in the fusioneer listings. Great work.

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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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Tue Apr 28, 2020 2:53 am

Mark:
Thank you, I hope I can get some fusion results soon! I was also interested to see if I could build an entry-level fusion power supply that was not XRT-based. I think I'll get one of those 30kv precipitator supplies as well and give that a shot.

Richard:
Thank you!! Now onward to neutrons!


I played around a bit more with the supply. I got a steady dull glow from the tungsten at 60-70 uA on the voltage measurement meter and 15-30 mV across the 10 ohm resistor which translates to ~25-28kV at 1.5-3 mA. I should be able to do fusion with this! One issue: my stainless steel input feedthroughs on the lid of the HV supply got really hot... hot enough to start melting the plastic. It started to bulge and I turned off the power before it melted through. The copper input wires themselves were barely warm. I think the higher resistance of the stainless steel really becomes and issue at these switching frequencies. I'll ditch the feedthroughs and just run the copper wires through the holes like I did for the HV output wire.

I found that my arducam was out of focus. Once I focused it, the image quality drastically improved! I just thought the camera was having issues in the low light, but nope, it was just out of focus. Great performance for $15!
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Dennis P Brown
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Re: Nathan Marshall - Fusor Progress

Post by Dennis P Brown » Tue Apr 28, 2020 9:51 am

Can't tell you how impressed I am with your home-built power supply. That is really an excellent, quality build.

Your total power (under a 100 watts) is on the low side so you will need a good detector system. However, using your smaller volume fusor (higher pressure deuterium), that power should, as you said, be sufficent to get detectable fusion.

Keep posting about the supply, too; maybe a circuit diagram would be nice. I'd be especially interested in the power supply for your ZVS. If you haven't already done this, maybe some details on how you made your 'flyback'.

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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Tue Apr 28, 2020 4:22 pm

Dennis:
Thank you for the compliments! I will draw up a schematic for the whole supply in the near future. I didn't realize that very few on this forum have gone for the ZVS/multiplier approach so I will try to document my results with it as thoroughly as possible.

I got rid of the stainless steel feedthroughs for the primary coil input and just pulled the copper wires through the holes. Then I soldered the output from the ZVS to them. This is performing way better! The wires just get a bit warm to the touch. I didn't expect the stainless steel to perform so poorly, but this is good thing to remember for the future. I am easily getting currents of 4 mA at 25-30 kV! The grid glows brightly and there are many hot pixels from x-rays showing up. After about 5-10 minutes of running, I turned everything off and observed that the outside of the chamber was too hot to touch! So I don't think I'd be able to handle much more input power anyways.

The main issue that I'm having now is a very infrequent spark happening around the connection of the HV supply to the feedthrough. It is very low power, almost like a static buildup spark. So it is definitely not arcing from the supply. It happens every 20-30 seconds when I get over 20 kV. The problem is that it shuts off my harbor freight voltmeter I'm using for current measurement! I tried coating the feedthrough connection with a lot of hot glue which makes the spark even less frequent, but it still happens. Any suggestions? In one of the attached pictures you'll see the voltage just under 30 kV (~75 uA on the meter), but unfortunately the current meter has been shut off due to the spark.

Edit: just pushed the system a little harder and registered a stable 6 mA at 28 kV!
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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Wed Apr 29, 2020 4:46 pm

I've drawn up a schematic for my current circuit configuration.
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Dennis P Brown
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Re: Nathan Marshall - Fusor Progress

Post by Dennis P Brown » Thu Apr 30, 2020 11:42 am

Thank you for taking the time/effort to provide the circuit diagram. I was wondering, what are the current/voltage values for the ZVS power supply diodes?
Also, what is the current out put/rating of the ZVS supply x-formers?

You know, if you keep up these excellent posts, despite my very sore back/arms from so much contrustion on my house, I'll have to mix and pour half a ton of concrete to finish the floor of my (still) future laboratory facility? I'm getting too impatient after seeing this work! ;)

Thanks

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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Thu Apr 30, 2020 3:24 pm

Thanks, Dennis! Perhaps I should stick a recommendation in the schematic for the bridge rectifier but I left it blank since there are so many options. I’m using a cheap MDQ 100A 1600V rectifier brick unit I had sitting around. It has screw terminal inputs/outputs. It cost about $10. Simple as that! I’m unsure of the current rating of the AC power transformers... they were salvaged from a dumpster. They are about the size and weight of a microwave oven transformer and output 15 VAC.

Good luck with the concrete, that sounds like quite the project... but having a nice dedicated lab space will be worth it!

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