Finn Hammer, fusor update.

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
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Richard Hull
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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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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 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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Dennis P Brown
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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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Re: Finn Hammer, fusor update.

Post by Liam David »

Wow, that looks fantastic! Looking forward to all the details.
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

A thing of great beauty for sure. Nice work. I am curious about your results with it. I have been totally successful with just packing silicone HV putty around every thing. Looks terrible. Works great. Not one air arc since I wadded in the HV silly cone putty.

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 »

@Liam
Thanks, I owe the basic design to you.
@Richard
The external flashovers can be controlled with potting, as you have done. Or with field controll like I did on the old one. Those two toroids doubled the voltage standoff from the rated 30kV to 60kV. I prefer field controll because it looks cool, and can be dismantled and modified.

In my previous experience, the fusion chamber attains it's clear see-through (lack of) atmosphere after a while
** with a red hot kathode**.
Therefore, my primary scope of investigation is to see, if a white hot kathode will be even better, and that is the reason for trying molybdenum as the material for the cathode. It should be good up to Incandesence.

However, more current is always good, and since more current means more heat, I want to investigate the effect of removing some of it. The surface area available for cooling is small so perhaps the effect is going to be neglectable. To find out, that is the reason of the experiment, but at least the cooling arrangemet will not add heat. Someone with a higher knowledge of thermodynamics than myself, is invited to suggest a better cooling medium than plain air.

In the name of collaboration,

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

Post by Matt_Gibson »

Very artistic! Definitely my style…I always shoot for form and function.
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Liam David
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Re: Finn Hammer, fusor update.

Post by Liam David »

I tweaked my CAD model to more closely resemble your design and did a thermal simulation. I put 100W on the (aluminum) inner cathode face and set the air in the (0.5" OD x 0.37" ID) copper tube to 20C.

Sim.PNG

Things get pretty toasty - hot enough to melt aluminum. The simulation doesn't include radiative cooling.
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Liam,

Interesting thermal image, thank you very much.

I have been wondering how the thermal "reach" of a colder stem would affect the temperature at the far side of the kathode, but your simulation shows that very well.
However, the old kathode melted on the side facing the stem, which had no more cooling than a 2.5mm stainless stalk could provide, (neglectible):

20210731_133359.jpg

From this I gather, that the old stem was heated to a point where it contributed to the kathode temperature, to form a hot spot at the stem/cathodetube junction. By cooling the stem, and reducing its cross section, I hope to reach a point, where the hottest area of the kathode is facing me, not the stalk. Both the stalk and the cathode is Molybdenum, with a thermal conductivity coefficient that is superiour to that of stainless steel.
Thermal conductivity coefficient : https://www.sciencedirect.com/topics/en ... oefficient
Copper: 386
Molybdenum: 143
Stainless: 25

The layout of the viewport is sub-optimal, because I view the kathode along the stalk axis, whereas if I viewed it perpendicular to that axis, I would have a view to the stalk. This was due to the initial desire to run a squirrel cage kathode, which did not doo well, and I am suffering from this decision now.

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

Post by Peter Schmelcher »

Keep in mind a Heat Pipe for cooling, lots of energy in water phase change. A Heat Pipe transfers heat far far better than a solid copper rod.
-Peter
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Peter,
I will read up on heat pipes, I have only a vague idea about how they work.
In this first cooling attempt, I rely on air to transport the heat away, and if the compressed air carries moisture to any significant degree, the plastic pipes wil turn into conductors. Lots to ponder...

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

Post by Liam David »

I'm not convinced that a heat pipe, or even an infinitely thermally conductive center conductor for that matter, would reduce the temperature of the cathode much. The heat transfer bottleneck is the cathode itself, as well as the rod that connects it to the copper, per the high gradient there in the image. In the simulation I've set the inside of the copper tube as a 20C boundary condition, which represents perfect, infinite cooling capacity. With forced air it will be much worse. Also, I simulated an aluminum cathode (239 W/mK vs 143 W/mK for molybdenum). All that said, I'm sure the cooling will prevent the copper and rest of the feedthrough from melting even when the cathode is red-hot.
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Liam,

That sounds good, since I am shooting at white hot ;-).

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

Post by Peter Schmelcher »

If the grid was a double walled cylindrical cavity that was a continuation of the heat pipe tube interior, then steam or water vapor will keep the entire grid under 100C. The heat pipe cooler end needs heatsink fins with moving air so the water condenses and runs back to the grid, no free lunch. CPU heat pipe cooling uses a lower than atmosphere internal pressure with water boiling at about 40C. Alcohol, ketone, etc. can also used in heat pipes plus wicks so the liquid returns without gravity assist.
-Peter
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Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Double walled cylindrical cavity, beleive me, I have been there, and good luck fabricating that one. Anyway, my goal is to prevent the kathode from melting, not lower the temperature to below 100 degC, I want it hot.
Fabricating a heat pipe means controll over the internal pressure before sealing it, and knowing how much working liquid to trap in it. Then there is the wick...
Not going to happen soon.
Then there is the radiator at the high potential.
Nope, no heat pipe just yet.
But thanks for the input , it widened my awareness of things.

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

Post by Finn Hammer »

All,

While the jury still is out, with regard to the success of my new Kathode assembly, testing it has produced the following decay graph, using Silver.

I have wondered why Richard and Bob both tout 5 second count intervals, and I now understand why:
While I erroneously figured that closer spacing of the samples would produce a smoother graph, actually this is not so. By taking the samples further apart, the values will be averaged and the curve will become smoother. Slightly coarser in the horizontal direction, but much less jaggedy in the vertical aspect. This will be incorporated in the future graphs,
For now, this is what I have.
In an attempt to validate the graph, or characterize it, or to find a way to recognize it as a Silver decay graph, I have drawn lines which are supposed to represent the expected decay of the 2 isotopes involved:
The red line represents Ag109, which activates to Ag110 at 89 Barns and should be dead after 5 times 24 sec = 120sec.
The green line represents Ag107, transformed into Ag108 at 35 Barns. This should lie dead after 5 x 2.42min = 800 sec.
The starting point of the green line is calculated like this: The initial count is 260 which I equal to the combined amount of capture Barns, which is 89 + 35 = 124.
The starting point of the green line should then be ( 260/124)*35 = 73

There are probably a lot of factors involved which makes this method invalid, I should hope so, because the decay curve is below the prediction all the way.

Input is invited.

First properly recorded decay curve.
First properly recorded decay curve.

Edit:

Here is a new decay from 8 minutes run, 20kCPM done by 27microns, 18 mA, 41kV and sampled at 5 seconds intervals. Much better.
This is on par with the best previous run, so still making neutrons allright.

5sec spacing and 20Kcpm
5sec spacing and 20Kcpm

Cheers, Finn Hammer
Last edited by Finn Hammer on Mon Nov 01, 2021 5:48 pm, edited 1 time in total.
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Richard Hull
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

The second graph is the one to go with. Plenty of activation here. You do not have the background that I have to deal with and it is much smoother than my 5 sec samplings.

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 Jim Kovalchick »

Finn,
Just a thought on drawing decay curves where there is multiple isotopes that hand off to each other over time. When trying to draw lines over the curves to match the actual decay as you did in one of your posts, it is best to plot the y scale in log because decay is an exponential function. If you plot your data that way, you will see straight lines that match the dominant decay constants.

Jim K
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

After the total meltdown, I decided to bring the fusor up to the standard that it should have been at to start with.
This involved the manufacture of a multitude of special cables for the turbo, the 901P’s, the baratron, the flowcontroller and several more.

Soldering the close spaced 15 pin d-sub connectors is ...... so satisfying
Soldering the close spaced 15 pin d-sub connectors is ...... so satisfying

I also built a remote control console, and this was getting obviously urgent, since I had experienced a couple of situations where I had that slight feeling of sunburn in my face after a fusor run. Lead is good, distance is better, and I can now operate the fusor from 18 feet of distance.

The remote console with readouts for Voltage, Current, Flowrate, Pressure, Transformer core, fet and chamber temperature, foreline pressure turbo speed, and a display for the professor with millibar and Pascal. Big round knob is the flowcontroller
The remote console with readouts for Voltage, Current, Flowrate, Pressure, Transformer core, fet and chamber temperature, foreline pressure turbo speed, and a display for the professor with millibar and Pascal. Big round knob is the flowcontroller

Finally I modified the new feedthrough that I showed off recently, but which developed plasma between the stem and feedthrough flange already at 40kV. This plasma formation occoured at below 15micron only, forcing me to initiate plasma at higher pressures, and work my way into lower pressure, and the associated higher voltage, but still limited to 15micron/35kV.
The solution was to manufacture a longer 6mm molybdenum stem for the grid, and shorten the 12mm cooling stem accordingly.
I will go into this in more detail in a following post.


The resistive divider I use is made from 30 pcs. 47M VR68 resistors in series, and the bottom is 3 pcs. 47k 2W resistors. Externally is another 22k resistor which compensates for the 1M parallel readout. The chain potted in the clear epoxy you use to make floors and river tables of, I use the slow curing version, good for up to several inches of thickness layers.

The resistive divider for the voltage readout.
The resistive divider for the voltage readout.

This has also proved to be a good potting compound for the voltage multiplier. My previous multipliers had 1K resistors in series with the diodes, but the dissipation in these resistors was approaching 3W each, as verified by LTSpice, and even the best heat conducting potting could not transport that heat to the surface. This led to destruction of the resistors, followed by arching in the void along the body of the resistors, and eventually big bulges showing up on the surface of the potting compound. I had to break the multiplier apart to find out the full story, and obviously this internal arching was a cause of a bad, flickering instability in the plasma.
In an attempt to remedy the problem, and also get instant insight to the individual parts of the stack, I tried to omit the series resistors, and use the transparent floor pouring epoxy, and this has held up so far, I consider it a success.


The voltage multiplier
The voltage multiplier

The foreline is monitored by a 901P, which is really the swiss army knife of vacuum technology. The internal set point relays, the RS232 communicating protocol, and the ability to emulate analogue output of 23 different transducers puts it in a class of its own, there are so many great things inside it, but then… it is made in Denmark!
In this setup, It is configured to emulate a 100 Torr Baratron, and one of the set point relays is set to control the roughing pump, via a solid state relay, so that it is running from atmosphere and down to 4 torr, then shut off from 4 torr and up to 10 torr, at which point it turns on again.
The manual is a bit ambiguous in defining the right commands for the set point relays, so here is what I feed it, to make it perform the desired functions:
Setpoints:
@253sp2!4.00E+0;FF
@253sd2!below;FF
@253sh2!1.00E+1;FF
@253en2!abs;FF

100 torr Baratron:
@253AO1!313;FF

Cooling system:
New manifold, components no longer on the floor. Run simultaneously with the power supply!


3 Fans trying to keep up with the heat released in the cube.
3 Fans trying to keep up with the heat released in the cube.


To get the many wires from the transducers, pumps etc. routed up to the remote, ..... I admit it, I made a mess here, but every single cable is documented in a spreadsheet, and so are the terminals, so I know where the wires come from, where they are going, and what they do. But pretty it is not.


The main electrical junction. This is where the controll cables for the 2 901P manometers, the baratron and flow controller, the turbo and the hv.powersupply and the household supplies meet the cable to the remote console.
The main electrical junction. This is where the controll cables for the 2 901P manometers, the baratron and flow controller, the turbo and the hv.powersupply and the household supplies meet the cable to the remote console.


Here is the other end of the command chain. It started out really neat, then developed into a mess.
Here is the other end of the command chain. It started out really neat, then developed into a mess.

Here is a view of the present iteration of the fusor

The fusor seen from the viewport side
The fusor seen from the viewport side


And another view from behind:

20211216_145336.jpg


However, the chamber displays the same clean atmosphere as before:

20211216_130851.jpg

And it payed off in silver dollars. after 3 runs at 12minutes each, the last one topping out at 60kV, 30mA activated silver to 45kCPM, twice as much as before, as seen in this video.


45kCPM run

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

Post by John Futter »

MOST EXCELLENT!!!!!
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Re: Finn Hammer, fusor update.

Post by Matt_Gibson »

I was wondering what you’ve been up to…Quite a lot!
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Dennis P Brown
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Re: Finn Hammer, fusor update.

Post by Dennis P Brown »

If the Germans' decide to build the next generation stellarator then you Finn should be the primary Engineer*! Impressive build to say the least. Nice you got the improved activation after all that work, money, and effort. Congratulations on a job so very well done; including the documentation you published here.

*Though even you might not have considered using large helium balloons to hold up the complex power feed lines for the stellarator's upper body - serious, if one wants to look at a beautiful yet silly engineering solution to a construction problem, that solution is both the most clever and fun I've every seen!
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Really fantastic! Remote operation is the way to go, be it at a range of 2 meters or 20 meters. To do this, however, is not for the neophyte DIY guy. Knowledge of system assembly, electronics to a deeper internal level, some cash outlay and the drive to do it are needed. As always, you build it....You know it! Every wire and item in the completed system was machined, assembled and placed there by your own hand. Any centralized computer or micro processor controlled element has been fully understood, programmed and debugged by you. Again, fantastic!

The term "you" in the above paragraph refers not only to Finn but to anyone looking to do what Finn has done. We who have really "been here" over time, have seen Finn arrive and have followed his relentless effort. He has been slow and confident after each step over the time he has been here. He has shared every time he has done something relevant which is what the term "open source" means in our credo.

We sadly saw Finn depart for a period with his promise of "I shall return".... Return he did! None were happier than I to see him come back. Hitting the fusion ground running, he has become somewhat of an icon in sharing his work. His work is not only inspiring, but of a high order that few here can be capable of in ability or in finances necessary to dive into the effort to this level which certainly exceeds any preceding "over kill" effort on fusion hardware perfection.

To set a goal equal to Finn's is certainly a bridge too far for 99.5% of any who might grace these forums. However, Finn's work shows what the right combination of the "right stuff" working behind a verve and drive to "do" can accomplish.

I must say that for my simple assessment, we are at a point in this effort where the power of what is seen today, in these forums, far outshines any previous effort seen here. We have more folks operating at a level in the amateur fusion effort than has ever been seen. Yes, I will also admit that those old glory and often gory days of clawing into rapid understanding and early vibrance coupled with the "doing" by many of we "old boys" are gone, but look what we dragged in here to supersede us!! Wow!

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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