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 »

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

Post by Mark Rowley »

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

Post by Dennis P Brown »

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 »

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.

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

Post by Richard Hull »

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 »

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.

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

Post by Jon Rosenstiel »

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 »

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.

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

Post by John Futter »

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 »

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

Post by Mark Rowley »

That’s very good info Jim. I’ll probably refrain from coating the walls. Not worth causing a bunch of instability with current control.

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

Post by Richard Hull »

This is the kind of discussion that will make this FAQ valuable. Open source experiment and discussion....That's the ticket!

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

Post by Jon Rosenstiel »

Richard,

I tried your suggestion of heating the endcaps with the chamber valved off. It was somewhat difficult to keep everything (pressure / current / voltage) under control but the end result was that heating of the endcaps seemed to have no discernable effect on neutron production. (Neutron count-rate from heating of the endcaps appeared to be no different than that from residual D2 already in the chamber)

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

Post by Richard Hull »

I figured it would be a bear to control the pressure/voltage and current valved off. Try running the system again, doing a lot of fusion. Shut off the D2 flow. This should cause glow extinction as the pressure drop to 0. Next shutdown the HV power (no fusion taking place) and in just a few seconds with the turbo on, the chamber pressure should plunge almost instantly once the gas flow is cut off. quickly valve off the chamber at high vacuum. You now have no D2 pressure in the chamber. Heat the end caps and see if the outgassing is D2 by doing the terrible balancing act of voltage, pressure and current. This should see if there is a hint of fusion due to outgassing of D2.

The key is to get rid of residual D2.

Remember the selection of chamber metal and even alloys affect absorption and desorption of hydrogen/deuterium.

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

Post by Mark Rowley »

This evening marked the 4th consecutive night I’ve ran the fusor for the purposes of “wall loading”. From a non wall-loaded cold start the fusor can hit a TIER of 1.5E+06 n/s. In this capacity it’s fairly thirsty for a moderate flow of deuterium and current. However, as I progress with daily loading runs, I’ve noticed the fuel consumption is much more efficient and the neutron output increases by roughy 50% or more. As of tonight’s run, I hit 3.89+06 n/s (101 bubs in 2 minutes at 17cm). If things progress accordingly the fusor should be firmly in the 4-4.5E+06 n/s range with tomorrow’s run.

The reduction of deuterium flow with such a high neutron output really amazes me. Gas flow can be throttled back to a pittance and the neuts keep on coming. I’ve yet to increase gas flow under these conditions but I’m guessing that will have a positive effect as well.

I can only attribute it to a heavy load of deuterium on the aluminum walls and very efficient cooling. It’s also important to note that I keep the chamber between 10-20deg C with ice cold coolant.

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

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Yes, I remember and have posted for years here, my daily rise in output prior to every HEAS event over several days. I have always attributed this to wall loading and the fact that I always did better right off the bat in each run group as days went on and then, each day hit a ceiling. I know that was due to the accumulated heat in the uncooled device run over time each day. When I hit that ceiling I would shut down with a bit more deuterium in the walls for the next day.

Thanks for the update and great data Mark.

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

Post by Bob Reite »

Once I cure my internal arcing, I will be able to do experiments with system as my vacuum chamber has a water jacket provision. Yes , I'll have to build a cooling system, but in theory I should be able to run tests in which the only variable that changes is the temperature of the inside wall of the chamber.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Re: FAQ - How to boost fusion in operation - Wall loading and cooling

Post by Richard Hull »

I write this to note that this is one of those FAQs where the replies add mightily to the content of my original PDF. Experiences will vary, person to person and over a larger number of different fusor designs, geometries, sizes and operational experience. This is what "open source" is all about and why this site is so valuable to the amateur fusioneer.

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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