FAQ - How to boost fusion in operation - Wall loading and cooling

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Richard Hull
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FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Richard Hull » Sat Nov 07, 2020 4:46 am

This is one of those rare FAQs where I expect a bit of discussion. So feel free to chime in as the paper asks.

The attached PDF paper is more or less a reduction or compilation of numerous ideas splattered over hundreds of past posts. Its points are a mixed bag of inductive reasoning and experimental results. Such a concise document seemed to me a bit over due. It is a FAQ due to the need for all who wish to do fusion might understand what it seems to take to improve fusion in an amateur fusor beyond an effort to just do fusion and then leave. In addition, a theory is advanced as to why this is so.

Richard Hull
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Mark Rowley
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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Mark Rowley » Sat Nov 07, 2020 10:38 am

Richard,
Fwiw I've found all this to be the case with my current system. The addition of two water cooling mazes (similar to Jon's) has made a significant difference (higher numbers and greater stability). Coincidentally, I'm gearing up for an iodine activation run and was planning on cooling the chamber to 0 deg C or below to see if any obvious difference is noted.

I've yet to do any real testing to see how far the aluminum chamber can increase output via loading but just after one run the difference is substantial. Perhaps 5 or more consecutive runs with the current cooling system would produce some noteworthy results.

Mark Rowley

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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Dennis P Brown » Sat Nov 07, 2020 10:50 am

As for wall loading, steel is highly absorptive of hydrogen and is one of the best metal's to do this.

As someone who added cooling coils to their fusor chamber, I will say it certainly made life easier not having the chamber get hot. I didn't think to compare before and after neutron counts, however. The system is not currently operational but I might revisit that in the future.

Your idea to cool the chamber very low (below 0 C) has merit. Might I suggest if anyone is interested, using propane is a very easy methodology; propane is far more efficent than any other coolant; an excellent insulator relative to high voltage, and both easy to obtain and inexpensive. The ideal coolant media.

Any refrigeration system can be converted to use propane (I've done this a few times - once for an AC wall unit and once for an indoor de-humidifier.)

Propane is non-toxic. As for explosive issue, yes one must remember this. But we use deuterium (isotope of hydrogen) that is very explosive. So proper plumbing (no leakages) is essential for safety.

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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Mark Rowley » Sat Nov 07, 2020 7:34 pm

Very aware of its merit which is why I’m doing it. But I’ll leave the propane cooling to you or someone else. The fire hazard is much more likely with propane cooling than with the tiny amounts of deuterium used to operate a fusor. I’d probably go so far as to say the safety comparison is apples to oranges. Very very different.

Btw Dennis, get your Fusor operational! It’s been way too long. It’d be great to see you employing some of the ideas you have on your system.

Regarding hydrogen absorption, is there a credible publication list of best to worst metals. This would have to be a list including machinable metals (steel, aluminum, etc) as it’s obviously not realistic to make a chamber out of lithium or similar.

Mark Rowley

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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Richard Hull » Sat Nov 07, 2020 8:57 pm

I will have to check or anyone can look up on Google "hydrogen absoption in metals".

Among the normally used metals are Titanium and Nickel (pure). Palladium is one of the best as is thorium. However, one would need to balance the absorption versus temperatures of loading and unloading to attempt to "tune" a reactor vessel to this process. We know that for 304 stainless steel unloading is thought to start around 100 deg C.

The ideal is a hydrogen loading at some temperature at or below room temperature of a thermally conductive metal or alloy that is affordable and which will only unload hydrogen at some temperature at or higher than the boiling point of water. A lot to ask, to be sure.

Richard Hull
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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Mark Rowley » Sat Nov 07, 2020 9:05 pm

Justin Fozzard has provided a few resources I’ll be looking into later this evening. Unfortunately the links dont seem to be working but I'll post once I get it sorted out.

Sputter coating titanium or similar to the inside of my fusor seems to be a relatively easy procedure. But as of this writing I have no idea about what temperature it begins to unload. If it’s in the “room temperature” zone I’d begin making the modification almost immediately.

Mark Rowley

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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Jon Rosenstiel » Sun Nov 08, 2020 2:15 am

Earlier this year while running a leak-up rate test on my aluminum cube fusor I noticed that the leak-up rate increased along with lab temperature. Early in the morning when it was fairly cool the leak-up rate was about 9 microns/hour. By early afternoon it was up to 54 microns/hour. To confirm that the change in ambient temperature was really responsible for the increase in leak-up rate I briefly warmed one of the cube’s endcaps with a propane torch. Within seconds the leak-up rate shot up dramatically.

Some weeks later I installed another set of endcaps which had been cleaned and baked out. After pump-down to base pressure I put the flame of a propane torch to one of the endcaps and saw no pressure rise. Today, after running my fusor for about an hour, I tried the same thing with the propane torch. Sure enough, shortly after the flame hit the endcap the pressure shot up.

So is the increase in temperature causing the aluminum to release deuterium, or is it something else, possibly sputtered-on material from the stainless steel cathode?

Jon Rosenstiel

EDIT 21:25 PST: I warmed the endcap's center only briefly, 10-seconds at the most. And considering that the endcap is 1/4" thick and machined from 6061 aluminum I guessing I raised the endcap's internal temperature no more than 20 F.
Leak-up rate after today's 1-hour run was about 9 microns/hour. Lab temperature of 70 F.
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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Richard Hull » Sun Nov 08, 2020 5:18 am

Very interesting and thanks for the report. My guess is that it was deuterium, A good test would be to fire up the fusor without pumping down, keep the chamber isolated heat, for only a moment the end caps. Build up a little pressure and raise the voltage. If the neutron counter clicks away, it is deuterium.

Richard Hull
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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by John Futter » Sun Nov 08, 2020 7:28 am

Yes BUT!
I could also be hydrogen from water adsorption in the system being disassociated by ionic conditions from the plasma IE H+ being liberated
Richards supposition is worth the test, if all deuterium then plenty of neutrons, if only a few then contamination from H+ and other ions

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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Jim Kovalchick » Sun Nov 08, 2020 7:58 am

Don't forget my recent experience with titanium liners. As my heat input rose, the outgassing of D made controlling current treacherous. I literally shutoff my D input, and chamber pressure and current were still rising. This effect happened after the first runs. So, I'm convinced that the titanium had both loaded and unloaded. It is not likely I will try to enhance wall loading beyond stainless steel performance without cooling ever again.

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