The cube just exceeded E+7 neutrons

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Finn Hammer
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The cube just exceeded E+7 neutrons

Post by Finn Hammer »

All,

I have had bubble detectors in my posession for a couple of weeks now, and am getting confident using them, keeping them warm enough in the cold workshop, and trusting their readings.
In this post I will describe the setup for running at the yet highest neutron flux.
The detectors have a sensitivity of 25 and 26 b/mrem respectively, and since it is hard to count more than 50 bubbles, I decided to place the detectors 35cm from the center of the cube.
20220206_124019.jpg

I have done several runs with a detector both in the position on the photo, as well as a detector right in front of the viewport, 35cm from center, and the results are comparable, no big difference. When I get more time, I will investigate the distribution around the cube in deeper detail.

Anyway, i have run the fusor up to the numbers shown on this picture:
20220208_120435.jpg


70kV, 32mA, 24microns.
Doing so, I get an interesting number of bubbles, yesterday, I logged 38-40 bubbles per 60 sec. but today, after a bit of conditioning, I counted 50+ bubbles, as you can (perhaps) count yourself in the following 2 pictures. It is hard to photograph the tubes due to reflections.




20220208_121723.jpg
20220208_121756.jpg
The detector has a sensitivity of 26 bubbles/mrem
The run time was 60 seconds
the distance from center of cube to detector was 35cm = giving a sphere of 15394 cm^2
1 mrem = 7.8 neutrons / sq-cm / second.

The calculation looks like this:
52 bubbles divided by 26 bubs / mrem = 2 mrem.
2 mrem X 60 X 7.8 X 15394 sq-cm = 1.53E+07 neutrons / second total isotropic emission rate.

The cube, the beefy powersupply, the good feedthrough, the molybdenum kathode, it all ads up.
It is good to be back.

Cheers, Finn Hammer
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Re: The cube just exceeded E+7 neutrons

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Re: The cube just exceeded E+7 neutrons

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Cheers, Finn Hammer
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Re: The cube just exceeded E+7 neutrons

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Re: The cube just exceeded E+7 neutrons

Post by Richard Hull »

The bubble detector is binned to a certain level and only counts fast neutrons which is what exits the fusor. (+/-10%, ideally). The ludlum counts slow neutrons at the detector, the detector will have some fractional number of the impacting fast neutrons on the moderator actually enter the tube and be detected.

In the case of my 3He system, about 70% of the fast neutrons hitting the moderator will be slowed and detected by my 3He tube. I do not know if the RBE between the fact that the bubble detector is detecting only fast neutrons which have an RBE of 5X over slow neutrons is figured in by BTI.

Their is much we do not know here 5/.7 = 7.1 that is approaching a crude factor of 10 differential. I would imagine the ludlum is calibrated to the human RBE as it is a survey instrument as hopefully is the BTI, being a dosimeter.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
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Re: The cube just exceeded E+7 neutrons

Post by Finn Hammer »

All,

I would encourage, that this thread stays focussed on the Cube, and its ability to produce neutrons, as measured by bubble detectors.
And also, that we don't wander into a characterization of the Ludlum 2363, since I am not referring to it at this stage.

@Richard:
I am not quite sure I understand your answer.
Have we not up to now accepted that a bubbledetector is a reliable (+- 20%) means of detecting fast neutrons? As far as I am informed, this is the standard way of calibrating fusors, as well as associated electronic neutron counters.

I know it must come as a chock to most here (I know I was) that a relative newbie, like myself, claims to have produced 1.xxE+07 neutrons, but that is what the detectors tell me, and that is why I submit the claim for my peers.

Today I did further runs, and it is probably no surprice, that the numbers kept climbing from run to run. Fusors are never the same from day to day, and today it liked 26 Microns, to land at 34mA with 71kV in. The first run netted me 42 bubbles, still a respectable number for 1.21E+07 neutrones/second, and the 7th, and last run left me with this detector, seen from 2 different angles:


Same detector from a different angle. 50 bubbles counted
Same detector from a different angle. 50 bubbles counted

Same detector from a different angle. 52 bubbles counted
Same detector from a different angle. 52 bubbles counted


50-52 bubbles in s 25bub/mrem detector. That corresponds to 1.47E+07 neutrons/second

Those 51 (averaged counts) bubbles could represent a reading equivalent to 40 bubbles or to 60 bubbles. even in the case of 40 bubbles, the cube still spits out 1.15E+07 neuts/sec.

So what can I say? Do the bubbles lie? What else can I do to support my claim?


Cheers, Finn Hammer
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Re: The cube just exceeded E+7 neutrons

Post by Joe Gayo »

It's completely reasonable for a cube fusor to achieve 1e7 at 70kV and 30mA. In fact, higher is possible at this voltage and current.

Nice work Finn. Stay safe.

Joe
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Re: The cube just exceeded E+7 neutrons

Post by Andrew Seltzman »

Those numbers sound entirely reasonable for the voltage/current.
All the bubble measurements are likely correct; varying output from a fusor from run to run is entirely common. Some runs likely had more output than others
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Re: The cube just exceeded E+7 neutrons

Post by Richard Hull »

The BTI bubble dosimeter will forever remain a king of sorts in emission rates to +/- 20%. ( I corrected my last post from 10% to 20%)

The reason is that the BTI dosimeters are binned to a very recent standard. After a few months, or at best, 1year they are shot. Part of their price probably reflects the days old calibration as they arrive at your doorstep.

My old post was based on the first reply to Finn's post by Matt Gibson that their seemed to be a 10X difference in numbers. I was interested in exploring the reason. Of course the difference could be in the distance between the two instruments. The BTI was far more likely to be correct, regardless.

Whoa there! It seems that post I referred to by Matt and a couple of others are deleted. I must have missed them. With the board in such a flux, I haven't been on the computer hooked to the internet all that often now.

The upshot is rely on any recent BTI dose readings and figure backwards. Use the average of several runs to calibrate a fixed position electronic detector like a 3He of BF3 system for all future runs as the BTI will die. Such is the best we have outside of a recently calibrated REM ball system which is RBE corrected for human dose rates based on a varying range of neutron energies. Which is as I, in the past, and Finn point out is generally 7.5 to 8 neutrons of 2.5mev energy per square cm per second which equals 1mrem/hr of dose equivalent flux at the point of measurement in a calibrated instrument.

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: The cube just exceeded E+7 neutrons

Post by Finn Hammer »

@ Andrew and Joe:

Big SIGH of relief. Thank you for your comments. For a moment there, I was of the impression that my reading of the bubble detector was off or not being accepted. I felt vulnerable, for a moment there.

@Richard,
The postings were deleted at my request, because I could see the thread wandering off in several directions, and I wanted to keep focus on the Cube and it's present performance.
It is new to me to have solid evidence of the performance, due to the recent acquisition of bubble detectors. The excitement I felt, and pride, was immense and perhaps I over reacted.

With regard to the Ludlum 2363, I will post some comparative measurements very soon, and hopefully others will follow up, in another thread.

Cheers, Finn Hammer
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Re: The cube just exceeded E+7 neutrons

Post by Richard Hull »

In the the vein of keeping the post cube centric..........

For those who can machine or purchase a ready to go cube, it seems the way to go. Especially if you are a very serious experimenter with skills and an exceptional HV supply of 60kv or above.

SS cubes are hyper expensive from LDS and with 6 ports to cover that can add up..........

https://www.ldsvacuumshopper.com/cubes.html

$1,421 for the 4.5" cube and $2,242 for the 6" is the cheapest I found.

Then the 6 X 52 = $312 for the true 4.5" blanks and 6 X 94 = $564 for the true 6" blanks This assumes you will adapt and machine those blanks for ports and windows as needed! Naturally a non-machinist would order some special ready to go blanks for window, gas ports and vacuum ports chasing these costs up by from $200 to over $400

A ready to go 4.5" cube might end up costing on the order of $2000 and a 6" about $2800.

While the pride of accomplishment and money savings to the machinist is always a delight, for the serious, non-machinist experimenter who will go the cube route will spend serious money.

As serious output for experimentation also demands input voltages exceeding 50-60kv, this puts another super burden on the average arrival here.

Even though I have the machines and can both machine and mill and weld, If I would jump into the cube biz I would opt. to spend the long buck on an all SS cube and fittings just to avoid issues such as tapping the myriad of holes for bolts. (48 for the 4.5" and 72 for the 6")

I know that others might go for the 2.75 cube which is barely a 3" cube for only about $500, but the 4.5" cube seems a minimum to me if you are going SS metal and really high voltage. Naturally, the 6" would be ideal

Finally. we have 3 cubist fusion artists here.

Joe Guyo, Jon Rosenstiel, and Finn Hammer. Is this currently correct?

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: The cube just exceeded E+7 neutrons

Post by Matt_Gibson »

Are the ready made cubes even the same as what our members here are making? They look to be boring all the way through a solid block of steel whereas the ready made ones look to be welded together. I wonder how the internal structures compare as far as performance goes?

I know a machinist (he works for me). I may see if he’s up for a special project :-)
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Re: The cube just exceeded E+7 neutrons

Post by Richard Hull »

No Welds! Read the intro page.

https://www.ldsvacuumshopper.com/cubes.html

No welds.... bored and machined out of a solid block of SS.

The more I look at them the more I like them....but those prices....

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: The cube just exceeded E+7 neutrons

Post by Finn Hammer »

Richard,
Cube centered is good, I will go with that, although initially I was more focused on having broken the E07 barrier, (don't read about that everyday here), but since that seems to be a no-event, lets just talk cubez..

Your arguments for leaning towards a factory made SS cube are well taken, but I see at least one obstacle, and that is cooling. You are going to need that.
If the goal is to activate silver to the maximum of the fusors ability, 13 minutes with 2kW input, that cube needs chilling. Not to mention a 1 hour run, or longer, to bring out the best in Indium.
An alluminum cube is easier to cool.
Then there is the cathode and the feedthrough, you are going to have to get your feet wet there, these parts need to be custom machined as well.
The power supply, is a real obstacle, I will give you that. Apart from the big SS monstrosity from 5 years ago, which went into the scrap bin, you may have noticed that I did not start building the fusor body, before I had the power supply up and running. At that time I saw Mark Rowleys 2000 fusor on a Facebook group, but when came back here and saw Jon Rosenstiels cube, there was no doubt: small, pretty and relatively straightforward to produce. But as soon as the fusor is up and running, the supply is everything.
I have shared schematic of that supply, and extensive build guidance for the voltage multipliers, so many should be able to replicate at least the multipliers.
I am reluctant to share the powersupply to any greater detail than the schematic, because there will arise an unsurmountable burden for support questions if I do. I tried that back when I pioneered the phase lead addition to the Solid State Tesla Coils (The Predictor) and suddenly I was met wih messages like: I built your circuit (but changed resistors x and y), now it doesn' t work, why?
It is a pity that knowledge is not instantly transferable, I would gladly build a complete fusing system in exchange of all the math and science I neglected to learn along the way, sigh, end of rant.

Cheers, Finn Hammer
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Re: The cube just exceeded E+7 neutrons

Post by Joe Gayo »

Finn,

E7 neutrons is a great accomplishment and very few have achieved this level with their fusor. I'm sure many want to replicate the results and hence the conversation about cubes. However, 2kW is a very high input power and the metric that will tell the most is a plot of n/sec/mA at a given voltage. The gain with current should be linear if you don't have another mechanism stealing efficiency. The gain with voltage is more complicated and depends on where the fusion is coming from (embedded or background neutral).

Joe
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Re: The cube just exceeded E+7 neutrons

Post by Finn Hammer »

Joe,

The only complete reference to E07+ I have been able to find is Jon Rosenstiel's https://fusor.net/board/viewtopic.php ... #p16489 where he spends1680w to get 1.1E+07 mark, and that at 10kV higher, so I thought I was doing all well, (1680/1.1)×1.5=2290, but I take your word for it, and I think that if I get a tighter chamber, performance, and efficiency, will increase. My bottom pressure is 4.8E-4, so obviously a bad leak somewhere.
I do, however, want to try to match the Ludlum 2363 to the Bubble detectors first, since taking such a neutrons vs. Current curve is much faster to make with electronic detection.

Cheers, Finn Hammer
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Re: The cube just exceeded E+7 neutrons

Post by Richard Hull »

Joe's admonition is well taken. My experience was that I needed a minimum of 800 to 1100 watts out of the wall to hit the mega mark in the past. Again efficiency of fusion is a total non-issue with me. All that interests me is just neutron numbers. I was not surprised at your 10e7 win. As Finn notes, Jon did it with his system, and the cubes have proved themselves in the hands of those pushing the envelope. I might suggest looking at the amps and volts, (VAR) feeding the variac if you use one to see what kind of real reactive power you are using out of the wall.

I tend to really hyper saturate the x-ray xfmr core in my system to get every volt over 40kv in my system. At peak back in the old days of fusor IV it was common for my input meters on the variac to read 255 volts At 8 amps, on my 1.35 x 10e6 run! The bulk of that heated the oil in my over driven magnetics in the x-ray transformer steel tank. It is bone laziness that keeps my from moving in my ready to go -65 kv 700lb 60hz power supply. This large item has reposed, covered up, outside my lab since 2012.

I avoid the switchers solely due to the fact that I know ceramic caps from my Tesla days. They do not like sharp HF transitions and in banks tend to blow off there "plates", (silver deposition on their titanate ends by degrees while in HF power service). Their capacitance changes over time as they snap and pop internally when over stressed. Each snap and pop blows off plate area. Spartan built switchers are costly to build at the fusion and fusor level above 50kv.

My old 60 hz system is still humming since 2001... I no longer champion it as it is "yesterday" and no one can get the systems any more that can stand the duty cycle of the fusor. All the dental x-ray systems since the 80's have been tiny switcher systems with the relaxed .05% duty cycle on-time at the average dental office. My 65kv 700 pound tanked transformer system came as a gift from a late 1960s XRF system being tossed from a college. The deal was, "You come and haul it away and it is yours" . To use it I would have to rework my entire back wall of my lab from the ground up. The last time I did that was in 2003 when I was a very young and energetic 57 year old.

In short, the cube is the system to have! Finn's point about cooling is the only reason I have not ordered an SS cube as I took into consideration cooling from the start of my thinking about the cube. I just will not do a cube, I suppose.

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: The cube just exceeded E+7 neutrons

Post by Finn Hammer »

Richard,
You said ceramic capacitors keeps you from switchers, in that case I have not documented my multiplier nearly as well as I thought. No trace of ceramics in it, pure polypropylene film all the way, a lesson learned in the Coiling days.
Here it is, foil caps, chinese diodes and river table epoxy potting, doesn't come easier to build than that:
Line the caps up in a box, solder the diodes, terminals and inter connections, and then just drown them in epoxy. Due to the diodes, keep it below 50kHz, for the sake of the ferrite magnetics, keep it around 30kHz.
The bubbles are half down the body of the caps, the level of the first pour, and way far from the high voltage action.
20211207_165858.jpg
Happy building!

Cheers, Finn Hammer
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Re: The cube just exceeded E+7 neutrons

Post by Richard Hull »

I put forward that this is why you are doing great. polypropylene and polystyrene are the ideal for HF work. Mylar heats up terribly. Micas are great but can't get the capacitance and are reserved for old radio work where they were rather bullet proof.

How many stages is that! Wow!

Your system is one of the best I have seen and your results show it.

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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: The cube just exceeded E+7 neutrons

Post by Rex Allers »

Nice on the multiplier, Finn. What are the specs on the diodes you used?
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Re: The cube just exceeded E+7 neutrons

Post by Finn Hammer »

Rex,

The diodes are chinese 2CL2FP with the following specs:
Reverse recovery 100nS
Max. Current continous: 100mA
Breakdown voltage: 30kV
I have tested them from 100kHz and down. They do not function properly above 50kHz.
Diodes are a strange breed indeed, as I found out during the development of the LLC switcher. But if these diodes are driven at around 30kHz, in a multiplier with a 50kohm resistor on the output, they seem to be unbreakable in fusor service.

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Re: The cube just exceeded E+7 neutrons

Post by Rex Allers »

Thanks, Finn.
That's about what I expected for specs. Good to hear your details on using them.
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Re: The cube just exceeded E+7 neutrons

Post by Matt_Gibson »

I’ve got those same diodes in my multiplier, just the 20kV variety (can’t find the 30kV on eBay). Mine have stood up to all kinds of abuse that my capacitors couldn’t…They’ll be going into my new multiplier.
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Re: The cube just exceeded E+7 neutrons

Post by Rex Allers »

Hi again, Finn.
I don't know why I didn't ask earlier about the polyprop caps you used in your multiplier. Looking at your pic it seems that the 'cap' for each stage is actually 3 caps in series, I assume for voltage increase, except for the bottom inputs which are two in series. Doing just a quick look online for vendors of HV polyprop caps, the one I found had some cylindrical axial lead caps, not the style you used. The cheapest listed was more than $10 each. I count 71 caps in your multiplier.

So, wondering, can you share approximate specs on the caps you used? Did you buy them new from a vendor or perhaps got a bulk deal a while back?

Curious about the best options if someone wanted to try to emulate your design, which sounds very resilient for a switcher HV supply. Any thoughts welcomed.
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Re: The cube just exceeded E+7 neutrons

Post by Richard Hull »

Throwing big money at a problem, even at the amateur level, typically results in a better, long term outcome that is stable. Even a thousand dollars spent on just the multiplier is a cheap price to pay for bullet proof 70kv resultant output that is rock solid in the end.

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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