Finn Hammer, fusor update.

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Richard Hull
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Knoll's book is a classic for millions looking to learn about radiation and detection methodology. You will use it as a reference. Europe is the home of metric and S.I. units. I tend to use the older units and the CGS system of metric when talking science. The only S.I. unit that is spot on for me is the Becquerel as the unit is small and handy. The Tesla is one of the most insane of all S.I. units. 6 Gauss is .0006 Tesla...(stupid). Seiverts and Grays have no place in my lingo. It's what you grow up with, I guess. I was taught poundals and Rels in college, but never used them in the real world. CGS metric is a true laboratory desktop frame system, thus I hang with it. (ergs and dynes). I went full metric in CGS and am still choosing English in Machine work, though on some projects I go metric just because I have good metric dial calipers on hand.

The Rutherford unit and the REP had very short half-lives of any unit for radiation measurement. You have to be reading texts from the 1950's to find those. Too, many instruments that still work well and even being currently manufactured in the U.S. are still reading Roentgens and CPM to have those units just disappear from "rad speak".

Scientific papers are only accepted in S.I. units. Have no fear, the S.I. units are just here for the time being until someone pushes for all new units and "proper speak" in the scientific community among the properly "anointed". We old boys will have to die out before some of the old units die in the speech related to radiation here in the U.S.

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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Re: Finn Hammer, fusor update.

Post by Rich Feldman »

How many radioactivity standards still use curies instead of becquerels?
Agree with Richard that the smaller unit is more handy and intuitive, though when applied to a freshly retired nuclear reactor core, it calls for rarely used large-number prefixes. I like the smallness of magnetic flux unit maxwell (gauss x cm^2) instead of weber (tesla x m^2), because it can be called "one line of force" in training classes.

Torr is an interesting unit 'cause it's no longer based on mercury (with adopted values for density at some temperature and gravitational acceleration at some place). It is exactly 1/760 of 101,325 pascals.

A couple of generations have learned to say gigahertz instead of kilomegacycle, and picofarad instead of micromicrofarad.
Those units and multiplier prefixes predate SI.

I hope my lifetime sees universal return of mega and giga to mean 1,000,000 and 1,000,000,000.
As they have always meant for resistance, frequency, digital data rates,
and data storage without an address bus.
It's ambiguous and unnecessary to call 1,073,741,824 bytes a gigabyte; that amount is a gibibyte (GiB).

Now back to Finn's fine fusor...
All models are wrong; some models are useful. -- George Box
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

@Richard and Rich

I appreciate your musings, personally I used to think that the Tesla was right on the spot, but then I was into building field coil loudspeaker magnets, where the saturation of the iron pole pieces happen at 2.1T. In the case of the permendure alloy, 50% each of cobalt and iron, 2.4T.
Anyway, to speak about the steampunk dragon, i took the viewport off last night, to align the cathode with the horizon, only to reexperience, how blue the hue of water vapour is.
After the night pumpdown, this morning things started to look a lot better, and I did another run, timed for 6 minutes.
Starting out at 44kV, ending at 47kV,
24microns more or less stable throughout the run
17mA trending towards 20mA at the end
0.8 Cubic centimeters of deuterium per minute
This produced 3.4Kcpm on the friskerprobe
Same old silver dollar alloy.
There is a mable leaf canadian in the mail, and it will get hammered to meet the diametre of the 44-9 probe, and thin of course, then we will see.....
It amazes me is, that although the cathode gets close to the melting point at 20mA/30kV, at 45kV it just trots along at 20mA, at nothing more than a brownish red. 45kV is the present sweet spot. I could leave it uncorrected for the last 3 minutes of the run.
I met with a physical limit today, during the initial burn in.
At one point, the pressure dropped to a level where the plasma extinguished, which caused the voltage to shoot up high.
A later test with a rolling camera, showed that at pretty exactly 60kV, the field controll on the 30kV feedthrough lost it.
https://youtu.be/xTBTRLbSff8

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Finn, welcome to the club! That is the exact thing that happened 6 times to me last year and the 7th time blew up my Turbo controller. Air will take only so much even with field control! At least it was external and did not track you insulator. Did it kill anything in your setup? I hope not. Now you know your "rope limit" in voltage within your current setup.

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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Re: Finn Hammer, fusor update.

Post by Mark Rowley »

Finn, oil is your friend! Trust me!

Too many folks here have thrown stones by claiming it’s “messy” or hard to deal with, thus establishing an unfair bad rap. Just like all disciplines in our hobby, take the extra precautions and you’ll have little to no issue.

All that aside, the aesthetics of electrostatic field control are an unparalleled art form.

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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Mark,

I know, you are right. In the voltage step up module, I feel tempted to switch to oil.
But in the feedthrough, I will stick to air. Todays experience was a positive one, because it tells me that to increase the voltage standoff ability, there must primarily be an increase on the toroids minor radius. If I had bothered to run simulations before manufacture, I had probably known this right along.
But at the time of manufacture I just wanted to create something that would look cool, be within the limits of my lathes and my stockpiles limits, and basically just be better than nothing.
It doubled the rated stand off voltage, less than I expected, but still steps in the right direction.
My high voltage background is Tesla Coils, a pulsed application. This is another ballgame, and the fusor is teaching new things every day.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

A couple of notes on my fusion progress.

I think perhaps the best thing that has happened recently, is the fact that I can now display a clean chamber, and know how to produce it. This is a great step ahead in the quest for meganeutrons.
(And a thanks! to Frank Sanns for pointing this out to me, last time I complained about a muddy picture):

Pretty clean chamber
Pretty clean chamber

The silver I used previously was 90% from a silver dollar, and in order to get clean silver in a rush, I called the coin dealer, he had a very corny Mable Leaf:

Corny Mable Leaf, but who cares, it is 9999
Corny Mable Leaf, but who cares, it is 9999

After a spin in the lathe, the ugly enamel,( or whatever it was, I didn't really care, being in for the silver) rubbed off, and it was time to hammer it out.
after a few annealing passes with the blowtorch, I finally filed it down to 0.4mm:

Setup for filing the foil
Setup for filing the foil

All that was left is a bit of scraps (and the 50mm disc, of course):

Scraps, together with a copper disc, to be activated on anlther day.....
Scraps, together with a copper disc, to be activated on anlther day.....

Without a proper moderator, the gain would remain unoptimized, so I made the, I guess now pretty standard 150mm x 150mm HDPE cube, with 40mm ahead of the foil, facing the fusor.
(I just now realize that it is only 100mm behind the foil and 40mm ahead of the foil, but I have more blocks to set that right.)

Pretty much standard neutron oven.
Pretty much standard neutron oven.

I seem to have reached the limit of the feedthrough, which shows intermittant flashovers, as can (perhaps) be seen on this picture:

Flashover at the base of feedthrough stem, in circle
Flashover at the base of feedthrough stem, in circle

I am importing some 19/20mm quartz glass for the better feedthrough pioneered by Liam David, which seems to be pretty universally used these days. With the individual users own small design features of course.

Anyway, I did a couple of runs today, all centered around 40-45kV, 20-20+ mA and 25-28 Microns 6 minutes. With the new silver, the new moderator and a cleaner chamber, this payed off with a 20K CPM on the Ludlum3/44-9 combination:


https://www.youtube.com/watch?v=QMVJYI11GV8


Since the neutron oven, the silver foil dimension, the counting apparatus and the probes all seem to differ from fusioneer to fusioneer, how can we compare our results to each other?

And is it possible to estimate the neutron output with the documentation I have given here, (foil is 130mm from center of fusor) I am starting to get courious about what numbers I am acheiving.

I would prefer to postpone the inevitable purchase of the bubble detectors until winter, where I can spend more time in the lab, these days I have to steal an hour here and there inbetween the practical tasks related to a house and garden.

A sure gottahave
A sure gottahave

If there is a will, there is a way, as they say, and fortunately the French do not appear to value the true original reference works, therefore I got this in the mailbox yesterday:
And it only cost me 25 dollars on french ebay, don't say there are no bargains anymore.

It is strange what it does, to have a book with the numbers, because I have probably read it a dozen times, that 3He has a large neutron capture cross section, but 5330 barns? Holy cow, With silver sporting 35 and 89 barns that number blew my brain.

So far so good, I guess I had better spend some time assembling some data collection hardware, so I can display similar fancy graphs as you fine folks are all doin.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Jim Kovalchick »

Finn,
That is a fantastic activation result! You could be easily activating other elements too. I may try more current with mine now that I've seen your result. I'm a little bashful about it though because I don't really know my supply's upper limit. Also, more current means more xrays.

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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Thanks, Jim

I am placing an order on a slab of 25mm lead glass, equivalent to 8mm lead, that ought to doo in front of the viewport. I plan to have it water jet cut into smaller chunks for sale to others that like me, still want to view the chamber real time.
At present, I have 6.4mm lead glass, so with a bit of distance I feel all right. The Ludlum 9 says 1mR/hour at todays runs.
I am searching the bible for stuff to activate.

Edit:

Jim, you gave me an idea to try out with activating copper:
A 1mm thick plate of copper activated to 400CPM in 5 minutes:

https://youtu.be/ytsX-5klGcM

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Tremendous results! You videos were clean and without any ambiguity for the folks in the know here. It is amazing what you have going there. That book is your guide and as you grow into the nuclear physics area the diagrams in the back part will become clearer. They are foreboding for the first pass reader. Vanadium is another standard for the advancing activator. Dysprosium is amazing! However, its two main activation isotopes decay via IT and are x-ray emitters. A gamma-spec is a better detector, A GM counter can be used for lower energy x-ray detection. A dysprosium coin can be had at....

https://www.elementsales.com/ecoins.htm

I have virtually all of the elements in my "element petting zoo"

For those new to activation issues I created a FAQ on amateur activation with a 5 page PDF on the whys and hows of getting it done with suggestions. Updated paper now in place 2021.

viewtopic.php?f=31&t=12251&p=79744#p79744

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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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Re: Finn Hammer, fusor update.

Post by Mark Rowley »

Impressive Impressive Impressive!!

Activating copper to detectable levels outside of gamma spec is the bees knees! You’re deep into the mega n/s numbers.

Are you still using copper for the cylindrical electrode? And is it pure copper or some type of alloy? And if you have it, can you show a picture of how you attached the small stainless post to the cylinder?

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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Jim, Richard, Mark
Thank you for your encouraging words

@Richard,

Vanadium. V51, 99.75%, 4.9 barns -> V52, beta emitter 3.76 minutes half life. should be doable.

Dysprosium is quite a riddle. There is so litle Dy158, 0.1% And then there are Dy160~164, each accounting for about a quarter of the volume, 130 to 800 barns, I don't quite know what to make of it, there is nothing in the coloum of "Principal means of production".....
I suppose during activation, the isotopes with the lower numbers will be stepped up to higher numbers, but still be stable, untill they reach Dy165 (through 800 barns) and more of it to Dy165m due to 2000 barns for that reaction.
The Dy165 has 139 minutes of half life, whereas Dy165m has a half life of 1.26 minutes, so due to the large crossection, and swift trip to saturation, it is the Dy165m we will see most of.
I guess this is where Camma spec. will shine, with the ability to single out the different energies from the different decay mechanisms. I am looking forward to getting my 63mm NaI(Ti) crystal online some time this coming winter.
Please correct me if I am wrong, I appreciate guidance.

@Mark

I am using a 15mmØ stainless cathode now. It is connected to the stalk with a 4mm thread. See attached picture.

grid.jpg

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Dy 164 is all you need to activate! It is stable, and over 28% of all elemental Dysprosium! So you are starting at the 800 and 2000 barn cross sections right out of the chute, the instant neutrons hit natural dysprosium. The only issues are the half lives of the activated elements. You have the neutrons in great abundance so you need not run for extreme periods to see something activate even to a low level with those cross sections.

The only elemental isotope of Dy to activate is the last one in the isotopic chain of the stable natural elements!! You will never change any of the percentages down a chain of a natural element regardless of the cross sections of the predecessors. In "nitpicker" math you will, of course! Let us take Dy161 with its great cross section of 600 with an atomic percent of 18.88 % the next one you will create by neutron bombardment is stable Dy162 which was 25.53% abundance. At the end of an hour you will have upped the percentage of Dy162 to 25.53000000000000000000000000000000006% there are countless quadrillions of atoms in that original 25.53 % upping that by 200million to a billion new Dy162 atoms is effectively zero increase in the atomic percent in the element of that isotope.

So when you see an isotope of any element that has a 45,000 barn cross section that will lead to another stable isotope of that element just below it in the table, just forget that beautiful cross section even exists. Always in a stable chain like that, go to the last stable element and check out its cross section and if great, see what it makes, what the radiations are, but more importantly, what is its half life?. A 5200 barn cross section that leads to a 50.6 year activation half-life is a non-starter. I discuss in great detail all of this in my paper in the FAQ on activation related to the many flies in the activation ointment for fusor users. There are all manner of nasty flies buzzing around the amateur fusioneer creating "catch 22s" when it comes to activation. Have no fear or worry, you will catch on.

Again that activation paper to be found at


viewtopic.php?f=31&t=12251&p=79744#p79744


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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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

The aftermath.......

I forgot to turn the waterpump on for another record attempt, and that would lead to a water leak which necessitates a rethink, and probably some hardware alterations.
On the picture, you see the top water manifold, which I made from PVC, a miscalculation from my side, because when the fusor body gets really hot, then even just the orings could distort the seating face to a point where a major leak was unavoidable:

Distorted sealing face of PVC manifold.
Distorted sealing face of PVC manifold.

So I had to dismantle the fusor to do these alterations, and this is what I found:

Firstly, the grid had melted, and of course right at the points which are out of the like of sight:

20210731_133212.jpg

Notice the pristine appearance of the alloy, not a single deposit of coloured metal.

20210731_133244.jpg
20210731_133335.jpg

Another thing to notice, is the signs of arching from the stem to the (now sputtered) surface of the Macor centering plug.
This has perhaps been the cause of the intermittent flickering of the plasma which I have had at times. This is also situated at a place where I cannot see it from the grid.
I think I did an array of poor design decisions with this feedthrough.


20210731_133359.jpg

Live and learn, this is a great lesson in high voltage plasma technology, and I will manufacture a new feedthrough, which will adress the arching problem, as well as provide better cooling of the grid, although I do not want it to get too cold: It is when it shines bright red that the cube really rocks!

The end plugs looks as would be expected:

20210731_133441.jpg


Edit: @Richard. Thanks for your ever patient tuition about (in this instant) activation: I had quite forgotten about the fantazillions of molecules in a sample.
Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Jon Rosenstiel »

Finn,

Wow, a real melt-down! My condolences.

I've spent quite a bit of time messing around with alumina tubes and Macor shields and what-not and have come to the conclusion that it was all a waste of time. In the end the standard feedthrough with a bare stalk was the most trouble-free.

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Re: Finn Hammer, fusor update.

Post by Jim Kovalchick »

I no longer use alumina. It always ended up arcing. I use a stainless steel tube conductor only. If the feedthrough insulator extends far enough into the chamber, shielding the conductor further is unnecessary.
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Re: Finn Hammer, fusor update.

Post by Mark Rowley »

Finn, I concur with Jim and Jon as those are my findings as well. No alumina or ceramic grid stalk enclosure/sleeve.

Regarding the meltdown, looks like you had quite the pool of “corium” on the edge! One more question on the grid, did you make it out of a solid piece of stainless rod?

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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Jon, Jim, Mark

I am glad you all agree, because what started as a macor centering device, (the stalk is thin and flimsy) soon got sputtered and turned into a short to ground. There will be nothing like that in the new design, which will, on another note, however, employ cooling, in an attempt to process more power.
@Mark.
When I gave up on the squirrel cage grid and switched over to the tube grid, I went to the industrial scrap yard, stainless booth, and picked up what looked like suitable candidate pipe bits for grid tubes. I have a collection of tubes from 1/2" to 3/4" in diameter.

20210801_001104.jpg

So, no solid rod here, just skimming a tube inside and out, and part it off.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

I will throw a me too in there as well. I started out in 1998 with alumina insulating stalks but by 2002 they were found to create more issues than they were worth. I use a naked 1/4" diameter SS stalk now to mount my grid on and no issues.

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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Re: Finn Hammer, fusor update.

Post by Albert Mery »

Hi, I've been following Finn's fantastic fusion work from afar and I have to say I have learnt so much from this thread. Very inspirational!

I just wanted to add to the topic of bare feedthroughs, I read in the IEC book that the researchers at Kyoto University have opted for bare metal feedthroughs in order to reduce the space taken up by thick layers of insulator present in most traditional feedthroughs, since, according to their calculations, for a classical feedtrough, around 50% of ions are lost to the stalk as opposed to the grid. Also the risk of arc-over due to sputtered material is avoided. So I suppose those are additional reasons for why you might opt for a bare metal feedthrough...

Has anyone experimented with cheap PVC as an insulator? Because I saw that one of the feedthrough designs mentioned in the book uses a fair bit of PVC which surprised me since I've read that It outgasses like hell and perhaps wouldn't be appropriate for the high temps of a fusor...

Keep up the good work Finn! Congrats on your latest activation results btw :)

Albert
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

PVC or any plastic just can't be allowed to enter a fusor and its ion/electron rich bombardment regions.

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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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Re: Finn Hammer, fusor update.

Post by Andrew Seltzman »

I also found alumina to be a poor insulator with arcing problems. Fused quartz or macor are excellent choices, with macor being particularly good as it is machinable.

Macor
Max. Temperature: 800° C
Dielectric Strength: 1,140 V/mil

Alumina
Max. Temperature: 1700° C
Dielectric Strength: 230-400 V/mil
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Re: Finn Hammer, fusor update.

Post by Dennis P Brown »

Ditto (do people know that one any more?) on a bare steel stalk as the feed-thru; had good success with that on my original large system (of which, I am FINALLY getting the last bit of work that needed to be done on my new system. Even obtained a large silver foil for my activation attempt.)

Finn, as always, great work on your design and build as well as your detailed explanations. Very useful for every one.
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Dennis, how could we ever forget?

https://m.youtube.com/watch?v=LhkwiJowIUM

Cheers to all, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

All,
It has been awfully quiet lately, so although this is a small thing, I thought I would just post a single picture of my new, and as of yet untested, feedthrough. It is right off the lathe and associated machinery, and dusty. Just could not help show it (off).

The previous kathode really was jerryrigged, yet produced respectable numbers. The cathode assy was dangling on a 2.5mm stainless rod, with no hope of getting any of the heat out to the outside. This feedthrough assembly has air cooling of the molybdenum kathode and is an attempt to place it in line with the rest of the fusors features, and will hopefully lead to even better neutron production.

a lot of work went into this one.
a lot of work went into this one.
Jeez, dust and crud really shows on photos
Jeez, dust and crud really shows on photos
Air is blown through the blue pipe.....
Air is blown through the blue pipe.....
It it works, I will give a full and documented description.

Cheers, Finn Hammer
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