Target Material vs Fusion Yield for D-D, and D-T Reactions

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Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Richard Hull » Mon Mar 08, 2010 3:39 pm

A lot of the better CF researchers have pushed into the very area you are discussing.

When results are seen and can't be duplicated, many fall back to a possible lucky metal lattice situation based on the way the metal was processed or handled.

It goes back to finding some expert metalurists willing to be on a team to study the D loading in controlled lattice structures. (if that is really possible) Another whole world in itself.

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Doug Coulter
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Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Doug Coulter » Mon Mar 08, 2010 10:38 pm

This is similar thinking to the "smart target" idea I spread at the last HEAS. If you could use Rutherford scattering to make a flood beam channel down along lines where the desired target material was (D in this case) you could improve the interaction rates considerably. If that is, the scattering isn't swamped by energy losses to the electrons in the target before that happens.

I have been talking to the Chem dept at Va Tech about this, they are finding me a crystallographer to work with one of their better inorganic chemists on this for us. To get things like this done on the good 'ol boy network for free takes awhile, but it's been in progress for some time now, so I'm about to check back with them and see, and have been studying myself. Sadly, monovalent hydrogen doesn't often take on the right places in crystals to make this fly all that well, and simple hydrides both don't have the right crystal structure, and aren't too stable at high temps and vacuums. There are some hints that trinary compounds with the other two things multivalent could work, but there's not much public info on say, the chemistry of U beyond some very simple compounds used in refining. I doubt it's secret, it's just that crystallography is considered a boring field by many and has it's own journals read only by other crystallographers....

Obviously higher Z atoms would scatter better -- but also are larger which cuts the percent of the desired stuff down, and make the incoming ions lose more energy per interaction. So the really best thing might be a surprise when we find it. Could be you're really close with Ti already.
Of course, if you could make the target out of other things too that would take part in a reaction with the beam, well....but even at what you call medium energies are far past what most of this group is willing to play with....not many chances. I think Be and B get interesting at fairly high energies -- and interestingly will get into fairly complex chemical compounds that may be good for this.

Chris -- neutron tubes are far better than most fusors (although mine is catching up fast) but!
With them there is a zero chance of recirculation, with a fusor we can still hope. I am now making transit time measurements and building high power video amps so I'm doing more than just hoping on that topic. As of course you are with your interesting idea....I doubt a plain jane DC fusor will ever have much, though.

I absolutely don't buy the idea that neutron tubes are "more complex" because in the design I've put links up here to many times, it's patently obviously not so -- they are if anything, simpler, especially if you forget the "sealed off" part of the normal requirement. It's the same stuff, just arranged differently.
The old '50s Phillips design had one cool trick -- the target electrode shape to prevent back acceleration of electrons. Not hard to duplicate at all...

The thing with them is that that's it -- there is little chance, outside of a "smart target" of ever improving one much. So if you just want a ton of neutrons, make that tube. If you want fusion energy, try something that has at least a chance of doing better than one strike per ion.
Why guess when you can know? Measure!

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Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Richard Hull » Tue Mar 09, 2010 4:15 pm

I'm with Carl on this. Neutron tubes are so good due to D-T's 100+ gain and if D-D, their 100kev + potentials. Amateurs, even the best here, work at 60kev max and use only D-D. Not much room for casual or inexpensive advance.

Of course, leave behind all hope ye who enter for power fusion; be it fusor or tube based.

Fusion beyond a certain number, maybe 10e7 or 10e8 fusions/sec, in amateur hands, demands complication and cash outlay that amateurs rarely have time, skills or money for. There might be rare exceptions, but the rule is in place and fixed rather firmly due to the physics, legal limits and costs involved.

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Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Doug Coulter » Tue Mar 09, 2010 5:40 pm

I left hope behind a long time ago Richard ;~} It'll follow you if you pull on the leash some, though.

And as usual you are right about a lot of things. Here at my lab we are looking at how to scale things *down* as our Q numbers get better -- too much of a good thing! There do appear to be some scale-dependent effects not in our favor for that, but we are looking at it. As you say, above a certain point all the radiation is a problem to deal with while we just want to learn how to do this "at all" -- we can learn how to do it big later if the results warrant that. The sheer amount of lead and borated wax is getting daunting around here.

Yes, the DT gives the first hundred or so gain factor in neutrons....now to account for the other few thousands difference in Q -- or just neutrons, since of course the DT has more energy output per reaction too.

Note these numbers are for neutrons per micro-coulomb, not per 10 milliamp-seconds...

I shake my head sometimes how people who get excited over a few percent error or unexpected small observed effect can't seem to handle the idea they may be off by many orders of magnitude in assumptions elsewhere.

In fancier systems (solid D or T targets , pulsed beams and such) people have done much better than this, this is from a 50's Phillips gas tube design handbook, and are numbers for a small sealed off tube running at 125 kv. Still nowhere close to net power gain, of course, but we have a looooonnnggg way to go with fusors to even get to here -- and again this is half a century old "state of the art" many of us could duplicate in an afternoon. Things haven't stood still in this field either, though as you say, at some point enough neutrons is enough, so they are working other areas (price and reliability for example).

I would further dispute that the pictured design is much harder to make than a fusor -- that's simply not so, this is very simple, especially if you don't want to make a sealed-off one. If you wanted to do that, you'd need some practice in making sealed off *anything*, which is indeed another step (I am still struggling for long life neon tubes here, but getting better), and swipe the D reservoir out of some old thyratron...The only cool trickery here is getting the focus just so -- not to a dot, but spread out to even out the heat load on the target. You will note the design of the target/electrode that prevents electrons from being back-accelerated much. Not hard to make at all.

They mention in the text here that a good ion source was one of the things foregone for simplicity and ruggedness, the one pictured reduces the yield a good bit due to not making very many monatomic ions. And it still kicks all of us around the block!

I plan to make one in a quartz tubing stubbed off one of the vacuum systems here and verify the numbers if I can at some point. But if you're after gain, this is a dead end -- stick a fork in this one, it's done already.

Here's the link again for those who RTFA, this is at the end of the chapter.
A drive in target is easy to make with the stuff you have already to have a fusor.
I note they only claim that T adds 3x, not 100x. I suppose this could be due to the non monatomic ions or something similar -- practical applications often deviate from theory that only covers some ideal case. But for us, that's *good* news -- it means we lose only 3x from these numbers for all D systems. If you just want a buncha neutrons, this is it. If you want gain someday, look elsewhere.

http://www.coultersmithing.com/OldStuff/pdfs/Pch8.pdf
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Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by lutzhoffman » Thu Mar 11, 2010 10:06 pm

Hello:

Thanks for posting the tube design, man it is pretty simple. One thing I wonder about is ref, to the ion source that they used. This looks to be an internal PIG source, which will give a broad range of species, when compared to a cleaner RF one, with 80% or more of d+1.

Doug: This has me wondering if in the one that you plan to build: If you plan to replace the stock ion source, with an RF/ Microwave based one? Construction wise it should be even simpler, and even cleaner from a vacuum perspective, just a closed off end of quartz, with a single pin electrode.

The pressure regulation could even be made via an induction / external heating based system, to avoid the extra glass / metal seals for the filament, etc. Kind of like they did in the old gas x-ray tubes with the side stub of glass, with a gas emitting contents inside. If you used Quartz this would be easy with an external heated stub.

The pin for the ion source tube end, could be made from an off the shelf Pyrex-Quartz graded seal, with a W pin in the Pyrex end. I am just mentioning this because W to Pyrex is the only HV seal which I was ever able to get to work right! So in other words it must be very easy : )

I would clean the sanded W in molten NaNo2 (Nitrite, not Nitrate), and melt a small bead onto it from a small piece of Pyrex tube, and then the rest was easy. I used the smallest Pur-Tung TIG welding electrodes, simply because I had them, but I suppose a more maleable form of W would be better. This would be a cool skill to have, to be able to do large D housekeeper seals etc. Take Care..... Lutz

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