Nathan Marshall - Fusor Progress

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Nathan Marshall
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Nathan Marshall - Fusor Progress

Post by Nathan Marshall »

Hello all,

Back in 2013 when I was 13, I learned about amateur fusor construction. Since then it has been my goal to build a working fusor. When I was 14 I made a simple demo fusor in a bell jar with an HVAC pump. It was extremely crude and extremely unsafe... but it glowed real nice! Since that time I have worked on many other projects relating to vacuum and high voltage, and I have slowly been accumulating knowledge on the subject and high vacuum parts to make a real fusion attempt. I no longer had easy access to my parents' basement where I worked on my projects once I started attending college in 2017. Between dual majoring in physics and chemistry, club activities, undergrad research, and summer jobs, I have had little time to work on my fusor besides school breaks. I find myself back at my parents' house now due to online classes as a result of the coronavirus. So lots of time to work on my fusor until my internship starts this summer!

Attached are some pictures of my vacuum setup and first plasma images. The vacuum pump is an Edwards E2M2 that was being thrown out by my university's engineering department. It was in nasty condition, but after some cleaning and oil flushes it pulls a deep vacuum. The HV source at the moment is just an oil burner ignition transformer running through a couple microwave diodes. It does the trick for producing some pretty demo plasma! The grid is 0.02" tungsten. One of the rings is a bit out of alignment in the plasma pictures. This will be fixed as I am currently making a more robust grid holder. I also plan to use four rings instead of three. The diffusion pump is an Edwards Diffstak 63.This past summer I took it apart and cleaned out carbon deposits on the jets from whatever setup it was in before I acquired it, so it is clean and ready to pump down. Vacuum measurement at the moment is with an Edwards APG-M on the foreline. I have a Varian ion gauge on the main chamber, and I'm currently building a custom cable to connect it to an MKS 919 controller. After I have that connection made I will begin high vacuum tests of the chamber. Next up is deuterium addition and the construction of a proper 30kV power supply. I have a deuterium bottle, but I still need to get the regulator and make a flow restriction setup. More progress to come!
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John Futter
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Re: Nathan Marshall - Fusor Progress

Post by John Futter »

Nathan
nice setup
not sure you require the fancy banyard alpert gauge head but good find
your demo pics are first class
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Richard Hull
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Re: Nathan Marshall - Fusor Progress

Post by Richard Hull »

Nathan, What the heck is all that burple and pink stuff going on? That is not normal, I would think. They almost look like leak streamers!

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall »

John -
Thank you! I got the ion gauge with a gauge cable for $30 which seems like a steal price. The filament still has continuity, but I have yet to test complete functionality. Hopefully I can get to that within the next few days when I make the proper connectors on the other end of the cable to connect to an MKS 919.

Richard -
Are you referring to the squiggly lines in the plasma pictures? Those are reflections of the grid glow. I’m looking down a length of 2.75” conflat with the viewport and camera, so I’m getting reflections from the inside of the tube in the picture.

For example, here is a picture of the fusor grid still glowing after the HV was just switched off. The reflections are really neat!
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Richard Hull
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Re: Nathan Marshall - Fusor Progress

Post by Richard Hull »

Man what a cool idea and polished system. I have never seen a mirror finish in any fusor system here, ever!!! Nice.

Joe Zambelli, back in 2001, had a mirror finish externally. Also, the only one of those I have ever seen.

viewtopic.php?f=55&t=11184&p=73754&hili ... lli#p73754

Thanks for the explanation.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall »

Thanks Richard! Wow, Joe’s fusor is a real masterpiece... a beautiful finish on that and perfect flange placement. I have to admit that the mirror finish on the inside of mine was a bit unintentional, the chamber that I got off eBay happened to have a pretty slick finish on the inside.
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Richard Hull
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Re: Nathan Marshall - Fusor Progress

Post by Richard Hull »

Indeed!! Someone, the original recipient, paid a gang o' bucks for all that internal polish. It is rather obvious it was never used to retain that polish. Maybe paying for it broke the back of the project. The thing looked medical grade inside. Musing wildly, could it have been used to test pathogen survival over lower pressure or near space vacuums?? This would mean that if it saw medical use its shine would not have been impacted. Not to worry, the instant you got a glow, any nasties would have been wiped out. A most interesting construct for sure.

Coating places might have ordered it so that once their specific coating polluted the thing that would be all that ever entered it as they would keep it under vacuum.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall »

I snagged an MKS 127AA-000.1C heated baratron for $60 on eBay. This has a full scale reading of 0.1 Torr, and a 1.33" conflat inlet! Perfect! I made a little power supply unit with a 24 VDC switching supply and a CCG154815D module that puts out symmetric +/- 15 VDC. I used a DB-15 breakout board and a cable to connect the supply to the baratron. It takes about 45 minutes for it to get up to temperature, not bad at all. I am happy to have a gas independent pressure gauge! I'm using my DMM at the moment to read the 0-10 VDC output from the baratron, but I plan on getting a cheap one from harbor freight to use as a dedicated readout for the gauge. So far the baratron works perfectly! I'm also working on a more robust grid design, a deuterium addition system, neutron detection with a Russian SNM-12, and the high voltage power supply. Things are coming along great. I have a month and a half until my internship starts... hopefully I can get some neutrons before that begins! My classes are all online but still no less work, so I have to make sure I don't put too much focus into my fusor. We recently studied potential gauge theory in my electromagnetic theory 2 class. Couldn't help but snicker at the idea that I am working on some "gauge theory" with my fusor ;-)
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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall »

I got the chamber outfitted with a conflat to swagelok adapter. I put a low flow metering valve and a hydrogen regulator on the line, and now I can tune the chamber pressure! I still haven’t hooked up the deuterium tank. I’ll wait until I’m ready for fusion and neutron detection. Also, I’ll add a shut off valve in the line as well since the metering valve doesn’t seal completely. I tuned the pressure to about 100 mtorr and got this beautiful star! The grid has been improved using a set screw coupler and a piece of copper to crimp the tungsten rings together. See this thread for more details on the grid: https://fusor.net/board/viewtopic.php?f=6&t=13364
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Mark Rowley
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Re: Nathan Marshall - Fusor Progress

Post by Mark Rowley »

Very nice!
What is the diameter of your grid and inner diameter of your chamber wall...or closest point to the grid?

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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall »

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 »

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 »

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.

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Richard Hull
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Re: Nathan Marshall - Fusor Progress

Post by Richard Hull »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall »

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 »

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 »

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 »

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 »

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 »

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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Re: Nathan Marshall - Fusor Progress

Post by Mark Rowley »

Keep it up Nathan, love the progress and Can-Do attitude.
I had limited success with the HF meters past 25kV. Exact same issues you and Jim have described and that's with copious shielding and grounding. Ultimately I opted for a nice Triplett analog meter which quickly solved the problem.

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Re: Nathan Marshall - Fusor Progress

Post by Richard Hull »

Analog metering will never display the precision of a digital, but they will be around a lot longer and do good enough in the HV realm. No one here needs to know 36kv to better than +/- 200 volts. Harbor Freight meters are not good in high RF or EMP environments.... Few digitals are. It is extremely tough to kill an analog VTVM or VOM. (unless you drop it on a concrete floor - jeweled movement) Digitals will usually survive such a drop.

Choose all metering based on where and under what conditions it is built for. Hamfests are the best place to pick up a venerable old VTVM or lots of specific analog meter movements that you can turn into anything you wish. I have so many meter movements purchased over my lifetime that I have them in several large, cataloged boxes stacked up in the lab from 0-20ua to 5 amps. I tend not to buy voltmeters unless they are 0-30kv or the like, scaled, and have 50ua or 100ua movements.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall »

Mark and Richard, you reminded me that I have an old analog meter that my grandfather gave to me years ago! I almost forgot about it. It has a 250 mV range so it is perfect for this application. I hooked it up and now even when the static EMPs occur there is no effect. The power supply is running great. The furthest I pushed it was 6mA at just over 30 kV. My Ludlum 44-9 probe starts to pick up x-rays even back where I am standing at that kind of power. So now I need to hook up the deuterium tank and regulator, and get some reliable neutron detection working.
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Re: Nathan Marshall - Fusor Progress

Post by Jim Kovalchick »

Nathan, I am certain you will be in the neutron club soon. I admire your careful work, especially the power supply.

Stay safe.

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Re: Nathan Marshall - Fusor Progress

Post by Victor Gonzalez »

Do you have a reason to use these 2 capacitors?

I have almost the same setup for a PMT (I used an lm317 for voltage control), and the voltage output with and without these 2 capacitors are the same.
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