Finn Hammer, fusor update.

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Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

The ballast resistor.
There are some chinese wirewounds that claim to stay within spec. both voltage- and powerwise, but given the urgency (which is, of course, more imaginary than real) and a bit of scepticism, combined with previous excellent experience with Ohmite's products, led me to the conclusion that there is really only one possible candidate for a ballast resistor, as aquired across the counter, and it is one out of the Power-mox series, from Ohmite.
Mouser has them, and the item shipped free from the US to Denmark, but then it is not exactly cheap either.
I have no doubt that it is worth every penny, now that it has been in my hands for a couple of days. This is what quality looks like:

Quality!
Quality!

Now, it does not come in the funky non-inductive style that "they" parade on their product page, because it is what we all would want if it was available,

Funky but non-stock!
Funky but non-stock!
Power_Mox_DSL.jpg (14.42 KiB) Viewed 10438 times

but apart from that, it is everything desirable, ceramic former, thick film resistive spiral and the coolest clear lacquer finish. And the 11 turns work out to 0.3µH, so what.....

Only complaint is the radial attachment lugs, I don't like them. Lots of sharp pointy edges, lots of places for corona to form. Corona, the dreaded mother of all arc discharges, the culprit of every surface track. Something had to be done, and what.. isn't that why I made that radius attachment to my lathe? so that I could whip up a nice couple of toroids in short order?
After another day in the workshop, this is what I had available:

IMG_20210606_101348.jpg

The toroids are mounted to the resistors collet style, not unlike some potentiometer buttons attach to the shaft (the good ones that don't mar the spindle with set screw marks) and some phenolic and FR4 trimmings to suspend the assembly.

The finished article looks like this:

DSC_4845.JPG
The rated power dissipation as I^2 x R losses is 50W, so it can support a continious current of 31mA to flow
The ballast resistor only sees the full voltage across the element for a brief flash in time, just when the arc strikes, otherwise the voltage drop is a maximum of 5000 x 0.031 = 158V,
(Edit: woops, should have read 50000, not 5000, for 1580V)
but the whole structure will be floating at whatever voltage I dare to throw at it, and since I don't want to use oil, and neither want it to arc to surrounding grounded parts, that is the reason for this litle exersize in field control.
The fact that it is also pleasing to the aestetic senses is only an added bonus.(Us seasoned tesla coil builders have an incurable, weak spot for toroids).

Cheers, Finn Hammer
Last edited by Finn Hammer on Sun Jun 06, 2021 1:53 pm, edited 1 time in total.
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Even in a dangerous pulse of current the voltage across the resistor will not reach a level to arc running end to end on the resistor, the voltage is near zip. At a run current of 20ma you are looking at 1kv across the resistor. (50,000 X.02 = 1000volts) The resistor would internally arc band to band, (assuming zero supply impedance), long before it would arc toroid to toroid in a pulse condition.

Unfortunately, there is the real impedance of the supply thrown in, buckling the output voltage and the plasma arc impedance within the arcing fusor. This limits arcing possibility within in the ballast resistor.

Still, you have closed all possible doors with this overkill. Slick, polished insulation on flat surfaces accumulate dust to create paths not expected. Those toroids are awful close to that surface.

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 »

Richard,

You see it all.
The dust is one aspect that I had not given any consideration, and although the assembly is being mounted upside down, with the resistor hanging, there is no telling what electrostatic forces can do to throw dust upwards.
I may have to redesign the FR4 standoffs for more clearance.

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

Post by Dennis P Brown »

I submerged my ballast resistor under oil; fully synthetic auto oil since that is actually superior to many transformer oils. It not only electrically insulates it but dissipates heat significantly better than air.
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

When checking out my x-ray transformer back in 2004 before installing it in the fusor IV rack system, I put my 63kohm, 100W ballast resistor in the tank with new HV silly cone diodes all in the oil. There it has resided for the last 17 years along with the diodes. Once pulling out the vacuum rectifiers and filament xfrmr back then, there was a lot of room for the new diodes and ballast.

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 »

Arriving back from Copenhagen, from my 9 day masonry assignment, one of the first things to do, was to bring the cube back to life.
I had left it with all valves closed, and pumped it down below 1E-5, which is the lowest reading on my current transducer, a 901P.
Immediately, I started to introduce deuterium, and settled for 22microns, then cranked up the voltage.
Getting stable operation is a breze, and soon it was running at 20 microns, 29kV and 12mA to produce, after 4 min. run, 700CPM on the Ludlum model 3 with the 44-9 frisker probe.
I did 3 more runs, finishing with a 10 minute run which was particularly good, because I found out how to bring the beast up to power slowly, which surprisingly made it possible to operate at 24 microns, 29kV and exeeding 15mA with the grid getting only a dull red. This produced in excess of 1000CPM.
The Canberra dosemeter started to report 500 microroentgen, so I stopped the operation of the fusor for this part, untill leadshielding is in place, and the Ludlum Model nine has arrived. At that time, I will swap the 30kV multiplier to a 60kV unit, and try not to break the feedthrough.

Edit. Changed CPS to CPM, these being counts from the silver foil made off a 1/4 piece of a silver dollar, hammered out.

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

Post by Richard Hull »

Finn, Great system! I retain a leaky fusor and can't restart as rapidly as many with a very tight system. I am sure it is due to my HV feed through. I am envious of those who can instantly restart a fusor to max function after a week or more of being left fallow, but sealed off. You have done great work and it shows. I need a minimum of three consecutive days of "conditioning" to obtain top level function. After that the next day I can blast right up in mere minutes as reported a few weeks back. A single week of inactivity will force at least two days to recondition. A month or more will need three days and 3 months, about 4 days. Just be glad you have a system that is well sealed.

As you know I created a nice little Arduino box slung under my fusor and imbedded a GM tube with silver or Rhodium wrapped around the tube in my 3He neutron detector moderator. I had the Arduino count for 10 seconds and record the count and sent the total to Arduino EEPROM memory. Then it counted again for 10 seconds and stored in the next EEPROM cell and so on. (This counting is initiated the instant the fusor is shut down) Then using the serial monitor in the Arduino IDE, I transferred, (dumped) the stored EEPROM data as a simple text file to a laptop via the USB port on the Arduino. I next blew the comma delimited text file into Excel to create a nice graph of the decay curve. Worked out great. I later changed the count period to 5 seconds. (only had to change one line of code). I will note that due to the variability of short 5 second counts in my rather noisy lab background, the curves look a lot better if my fusor is cranking out 7.5e5 or more n/s TIER during the activation period.

There are so many cool things one can do like this. Naturally, you can no longer swap, with any ease, activation materials by doing the above, but it does allow for two detection methods in one moderator i.e., electronics and activation which can be seen and proven in a demonstration rather quickly. One can still have a "neutron oven" near the fusor for rapid swapping of different elements for activation if desired.

I just found it interesting rather than to demo my fusor with a screaming electronics neutron counter, while doing fusion, to show that the instant the reactor was cut-off, (dead), have a new count now issuing from a radioactive neutron activated element which the neutrons created and to see the decay plot match the decay curve predicted. Many folks do not demo their reactors on a regular basis. I spend many moments demonstrating my fusor for interested persons and groups. I found activation a great way to prove to skeptics that I had done fusion. I often find that a person or people I demo the system to will tell others who are incredulous and unbelieving. This will usually setup yet another demo, in future.

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 »

With the 60kV greinacher in place, I did a 4 minute run at 40kV today, 25 micron and averaging 15mA, to do activation of 90% silver/10% copper, from my crummy piece of hammered out silver dollar.
This produced 2400 CPM on the 44-9 frisker probe. This is a new record for me.

It is interesting that the tube cathode seems to heat up to a lesser degree at 40kV than at 30Kv, same current, I would have guessed the opposite, not that I am complaining.....

A new instrument came in the other day:

20210713_130957.jpg

With this in hand, I could measure the radiation from the running fusor, and at 30kV, 20mA it generates 0.4mRoentgen/hour at 2 feet distance from the front face of the fusor.

This was without lead shielding, however the viewport has a quarter inch of lead glass. this glass is the equivalent of 1.6mm lead, which I was able to confirm by exchanging it with a piece of lead that thickness.
Running the fusor without the leaded glass, the radiation shot up to 3.6mRoentgen/hour.

I am waiting for this book to arrive:

Radiation Detection and Measurement
Glenn F. Knoll

Simply because it is not at all obvious how the different units relate to each other. I do know there is a factor of 100 between roentgen/hour and sieverts/hour, so that 0.4 mR/Hour translates to 4µS/Hour, and using this chart:
radiation.png

I deduce that 10 hours of fusion will put me square with a traveller by plane from NY to LA, which should not pose any concerns. For now, at least.

How to get from Sieverts to REM is another ballgame, but hopefully the mentioned book will fill me in on that aspect.

Anyway, nice to run and tweak the fusor.

If I should say something central about the cube fusor/cylindrical Kathode configuration it is this:

The cylindrical Kathode will quite possibly save the newcomer from one inevitable setback of the traditional grid: The meltdown.
The possibility of including water cooling of the body and endcaps at design time means that the fusor can run for hours on end without overheating. I have done 20minutes at full bore, with only a 15 degC raise of temperature.
But to get the best of these two hardware features, the access to -and ability to operate- a lathe, is mandatory.

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

Post by Rich Feldman »

Belated applause for the ballast resistor with anti-corona toroids on the ends. They are solid aluminum, right?
A work of art and science!

I was reminded of it last weekend in San Jose, California (at 4th and Taylor).
20210711_164123.jpg
Perhaps for safety around the exposed neon, which had been left "on" that summer afternoon.
All models are wrong; some models are useful. -- George Box
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Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Rich,

Noticing things like that is a sure sign of highvoltageitis. I suspect many of us have it. Thanks to god, we don't have to suffer from it.

Below is the present lash up, I am starting to see the wisdom in having the high voltage feedline coming down from above.
20210716_154215.jpg

Cheers, Finn Hammer
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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.

Mark Rowley
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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.

Jim K
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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

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 »

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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Finn Hammer
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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
Jon Rosenstiel
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Real name: Jon Rosenstiel
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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.

Jon Rosenstiel
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