Nathan Marshall - Fusor Progress

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Richard Hull
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Re: Nathan Marshall - Fusor Progress

Post by Richard Hull » Fri May 08, 2020 3:41 am

I always open the tank valve jsut barely to watch the low bressure gauge go to 4 PSI into my CO2 cartridge tank and immediately turn of the main tank valve. The little cartridge at 4 PSI will run the fusor for 10-20 minutes. I have never nor will I ever leave a main tank valve open regulator or no regulator attached. It stays hard off always until I need to let more into the little catridge at 4 PSI.

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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Dennis P Brown
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Re: Nathan Marshall - Fusor Progress

Post by Dennis P Brown » Fri May 08, 2020 10:00 am

As for hearing the leak through a failed regulator; yes, you should have. It appears the tank emptied before that, which can only happen if the tank's main valve isn't fully closed or its 'pressure relief' valve failed at some point (my lecture bottle has one of those relief valves - don't know if all do. The main valve does not seal that off.)

No matter. Your next concern is getting deuterium so generating your own is the most straight forward, I'd think; and a number of people have done that here.

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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Fri May 08, 2020 2:39 pm

I do have 10mL of heavy water on hand, so I can generate some deuterium with the PEM cell and use a syringe to store it. I got the gas line set up for that now this morning. I just need to dry out the PEM cell from the water that was in it before I put in the heavy water. Also I will do some tests to make sure my connections with the syringe are air-tight and see if I get flow rates in the 1mL per minute range. But at the moment I have a quantum take-home final exam to finish so I will prioritize that.

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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Fri May 08, 2020 11:06 pm

I generated some hydrogen, stored it in a 60mL syringe, and fed it into the fusor. The fusor was sucking in gas at quite a high rate, so after throttling off the diffusion pump a bit I was able to taper off the gas consumption. Even after these adjustments it was still quite a bit higher than 1mL/min. Attached is a picture of the plasma. This time I found that to get a plasma in the ~25kV 2-5mA range I needed a pressure on the baratron of about 16 microns. So this is quite a bit lower than what I got with the deuterium from the tank. I'm guessing this points to the lesser purity and potential water contamination of the generated hydrogen. I'll keep playing around with this a bit more and then consider filling the PEM cell with some of the heavy water that I have in my element/chemical collection.
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Edit:
So I did another hydrogen run this evening after some more work on the quantum exam. Feeling pretty good about my answers now. This time I was able to establish a stable 1.3mL per minute flow rate into the chamber with stable 3-5mA 25-30kV plasmas at ~12 microns on the baratron! After the hydrogen run, I brought the chamber to the same 12 micron pressure with just air as a control test. As expected, the electrical characteristics were completely different! At 5mA the voltage was <8kV. Below is a picture comparison of the two plasmas.

Hydrogen at 12 microns, 28kV 4mA:
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Air at 12 microns, 7kV 5mA:
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Cai Arcos
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Re: Nathan Marshall - Fusor Progress

Post by Cai Arcos » Sun May 17, 2020 11:47 am

Nathan:

First of all, I want to express my gratitude for all the details provided about a superb build, especially the affordable power supply.
I myself intent to imitate your efforts using a transformer I have found from a tube based CRT TV. The only problem are the capacitors themselves. The only item that I found on Ebay that is affordable on my budget is a set of 100pF 20kV caps. Even if I could connect two in parallel, that would still be 200pF, substantially lower than your own values. I understand the principle of operation behind a voltage multiplier, and thus know that the necessary capacitance depends on the frequency. From your own values, I assume that the frequency must indeed be high, however because I don't know the frequency of operation (which I suppose would also vary with the transformer itself) I can't perform the necessary calculations myself in order to check if those capacitors are adequate.
I would highly appreciate if you could use your experience and observations to guide me.

Thank you very much:
Cai

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Re: Nathan Marshall - Fusor Progress

Post by John Futter » Sun May 17, 2020 6:29 pm

Cai
you also have to consider trr of the diodes which is why high voltage power supplies are lower in frequency than ordinary switch mode supplies

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Re: Nathan Marshall - Fusor Progress

Post by Cai Arcos » Mon May 18, 2020 6:33 am

John:
I plan on buying 20kV 20mA diodes, with a trr of 100ns.
The capacitors are what worries me most, because everything else I've found with similar capacity and voltage ratings breaks the bank in my birthday fund.

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Re: Nathan Marshall - Fusor Progress

Post by Dennis P Brown » Tue May 19, 2020 10:07 pm

Cai, you should start your own thread with such questions rather than continue on this thread.

As for voltage multipliers (I built a monster one of over 100+ kV using large door knob caps), one does not need a full wave system (as shown in his drawing) - a half wave voltage multiplier (while, of course, half the power) can provided the same high voltage. This will save a good bit in cap costs (half the cost.) The issue is power - this will make or break a fusor supply.

I've found (rarely) large caps available for a reasonable price on ebay (but I wasn't looking for any at the time.) Deals appear and one must be ready and be patient till the desired deal occurs. The only way if one is limited in funds. Don't buy random stuff hoping it will work. If you are trying to copy his supply, (and it is proven to do fusion) then you have little choice in the design. Trying to develop one's own design/variation without the required knowledge (be unable to calculate the results using x,y & z components) is very likely to result in failure.

A ZVS (a high frequency driver supply) requires a very high current supply so those x-formers need to be beefy - as seen by his dual x-formers used in his system. I don't think a CRT display will do the job.

Note, I believe that the flyback used in his supply isn't standard (most commercial fly backs are way too under rated) - I believe he wound that himself (maybe just the primary but I'm not sure - that you should ask before buying parts). Relative to the secondary, maybe that is commercial but if not, winding that is very difficult. That isn't what most inexperienced builders try to do - for a flyback one issue is that the required x-former parts that will work aren't easy to find; and second, if one needs to make the secondary, wraping the HV section requires building the special winding jig/tool. For his supply, that fly back is the key item that make his HV system possible - the multiplier is just a small part of that construction project (and the easiest to build.)

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Re: Nathan Marshall - Fusor Progress

Post by Cai Arcos » Wed May 20, 2020 7:00 am

It was not my intention to derail this thread, and as you say a new one should be started.
I thought it was acceptable, since I only wanted to know the operating frequency (since I can calculate all the other things I need from it),but I suppose I will just have to find out.

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Nathan Marshall
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Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Wed May 27, 2020 6:36 pm

Cai:
I just measured the input frequency from the ZVS Driver and it was about 50 kHz. See the attached oscilloscope shot of the input waveform:
IMG_5797.jpg
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The flyback transformer that I am using is an old Thordarson FLY337 that I bought on eBay. It is a large open frame AC flyback. It is far larger than any flyback I've ever seen. I used the stock secondary coil. I cut out the primary and wound my own with 8 turns of 12 gauge solid copper wire.

I made a YouTube video documenting my fusor setup as well as a fusion run. Here is a link to the video: https://youtu.be/enId-kWrdz4

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