Colliding beam mystery

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Rich Gorski
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Colliding beam mystery

Post by Rich Gorski »

Hi everyone,
Here’s more NPR data from my ring accelerator fusor with two 40 degree ion sources. This is difficult to explain so please chime in with thoughts.
The test performed was to compare the neutron count using the two ion sources together in a colliding beam mode and then run separately. Call them ion source A and source B on opposite sides of the chamber. Here’s the data for a 35kV run with each ion source producing 10mA of current as registered on the -HV PSU. The pressure was steady at 1.4 microns. Neutrons were measured with my GE B10 proportional tube with Vbias at 742V over a 1 minute time period. Also note that the ion sources were run in pulsed mode with a 25% duty cycle.

Source A run alone. 2216 CPM
Source B run alone. 2728 CPM
Adding the CPM = 4944 CPM

Now, thinking simply when both ion sources are run together in the colliding beam mode I might expect the neutron count to be something near the 4944 Value. Actually I was hoping for a bit more than 4994 CPM due to the addition of some beam to beam reactions taking place in the center of the chamber which I expect at 1.4 micron pressure. The MFP is larger than the 8 cm distance to the center of the chamber so there should be a significant number of max energy ions that reach the center. When both ion sources were run together colliding here’s the results.

Source A & B together 4348 CPM This is 12% down from what I might have expected.

Anyone have any thoughts why the count has dropped 12% when both ion sources are energized and in colliding mode? I have repeated this test several times with very similar results. So the reduction seems to be real and not a statistical fluke. My only guess at an explanation has to do with what Richard calls velocity space. Could the colliding beam situation be reducing the average (whatever average means) velocity that ions can achieve? So, on the average ion energy is reduced somewhat?

Thanks,
Rich G.
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Richard Hull
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Re: Colliding beam mystery

Post by Richard Hull »

I assume you just had the acceleratory voltage out of the extractor and not the HV voltage on the cathode for a pure beam on beam collision??

If so, then you might not have had any beam on target value as with a single ion gun and full cathode voltage might offer better results due to the high cathode voltage.

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
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Re: Colliding beam mystery

Post by Rich Gorski »

This ring accelerator is not a pure beam on beam device. There is no extractor grid. The ion sources are of the anode layer type. Same as those that Andrew Seltzman has reported on here which consist of an anode electrode, a cathode electrode and a perpendicular B field. My sources differ only in their geometry being essentially slit orifice sources where Andrew's were circular. The ion beam exiting the ion source has the energy imparted to it by the potential difference that exists between the anode and cathode of the ion source which in my case is between 500 and 1000 volts, So the ion beam exits the ion source with less than 1keV of energy. The grids following the ion source function to both accelerate and focus the beams. My post below contains photos of the device as well as a computer simulation showing the potential distribution between the various grids.

viewtopic.php?t=14846

If there is BOT interactions in my device, wouldn't we expect that value to be double with two beams instead of one just based on symmetry?

Another thought occurred to me that might explain the reduction in NPR. Space charge. The space charge from the positive ions would work to diminish the negative potential near the center. Could this be significant enough to reduce the ion energy... and two beams would add more positive space charge than one... but doesn't that mean more electrons drawn in too?? I'm confused :).

Rich G.
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Liam David
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Re: Colliding beam mystery

Post by Liam David »

Does each ion source have its own power supply?
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Re: Colliding beam mystery

Post by Frank Sanns »

Colliding beams will act to defocus the individual beams due to electrostatic repulsion interactions. You may or may not visually see the because the visible plasma is electrons recombining into the atomic orbitals rather than an indication of fusion.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: Colliding beam mystery

Post by JoeBallantyne »

RIch -

What numbers do you get if you run each individual ION source at 20mA?

Run ION source A at 5mA 10mA and 20mA, and tally the neutron numbers.
Run ION source B at 5mA 10mA and 20mA, and tally the neutron numbers.

Then run A+B at 5mA each (10mA total current) and 10mA each (20mA total current) and tally the numbers.

Then you can see how 10mA and 20mA total current works for A, B and A+B.

I'm not actually surprised that A+B was a little less than the sum of each. The chamber will likely be getting hotter, so more outgassing, since 2x the power going into the device. Plus, its just how reality almost always works - not as you would expect, and worse than you predict...

When running A+B, are the pulses for turning the ION sources on and off exactly synchronized - so that both ION sources are on at exactly the same times?

The interesting thing to see, is if A+B NPR is greater than individual A NPR and B NPR for the same total current.

My guess is that it likely will NOT be greater. At least not in a statistically significant way.

Because if you are getting reasonable recirculation, you will get beam on beam collisions when running just one ION source. And if you are not getting decent recirculation (more likely - you are probably going to get 1 or maybe 2 recirculates at most) then adding an opposing ION source is probably not going to make much difference. The more recirculation you get, the less difference adding an additional source will make when the total current is held constant.

Joe.
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Re: Colliding beam mystery

Post by Rich Gorski »

Liam, Yes the ion sources have their own supplies so I can dial in their current levels independently. As you can see from my NPR numbers they are not identical. Probably geometric differences due to my limited machining capability.

Frank, agreed that the colliding beams will tend to defocus but will that cause a reduction in total A+B NPR and if so why?

Joe,
1) I will test at 5, 10 and 20 mA as you suggest (not sure I can get to 20ma on each ion source without increasing the pressure but we'll see).
2) Ion sources are not perfectly in sync since mechanical relays do the ion source switching. That's why I'm running with a long 1/2 second on time so both beams should be on for most of that 1/2 second.
3) Didn't think about outgassing as a potential explanation. Maybe... but after the entire test (and with 25% duty cycle) the chamber is just barely warm to the touch. I could test that by running A+B at say 10mA, repeat, repeat a third time and maybe a 4th time. If the NPR drops with each run then outgassing is a likely cause.

Thanks everyone
Rich G.
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Re: Colliding beam mystery

Post by Richard Hull »

There you go! Many viable and varied ideas on what is happening. More experimentation and data collection, as suggested above, might throw a bit more light on the situation. One wonders on just how tight parameters can be held repeatedly, run-to-run. Given a specific HV drive limit, varying the current might be the key.

It is to be remembered that we are tunneling by the grace of quantum probability. Data done at our level is never going to be even one sigma run-to-run between extremes over a significant number of runs. We, after all, are rolling the quantum dice in velocity space rather that creating a pure thermal plasma. We do it like hash browns....Smothered and scattered.

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: Colliding beam mystery

Post by Rich Gorski »

Richard,

So true... many variables, low repeatability, measurement inaccuracy... but even through all that the 1/2 dozen times I repeated the test, the data always goes in the A+B < (A alone + B alone) direction. Not once did it go the other way so far. Maybe we'll learn something from this, maybe not, but its fun for a retired engineer.

Rich G.
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Re: Colliding beam mystery

Post by Richard Hull »

I, too, am a retired engineer. I was use to a high degree of precision in engineering, but had to learn about nuclear slop in fusion due to the Quantum tunneling game coupled with the small numbers we bring to the fusion game at the amateur scientist level. Early on, in 1998 when we were new to the game, our neutron measurements were order of magnitude range in verification. (Again, neutrons can't be detected to the single neutron, being neutral) All measurable reactions are second order detected reactions and even those are subject to the detection cross sections, (more Quantum probability stuff). This is a fixed rule even the detection game.

We have all known that counting neutrons, even in the most controlled conditions is a +/- 10% limitation. However, we can arrive, under carefully controlled conditions, at a 1% error in differential measurements. Such accuracy is obtained in locking down the detector position relative to the fusor, making upgrades, modifications to the fusor, re-running under the exactly controlled equivalent condition and comparing data against a previous run.

What you have done is a significant differential, provided all is maintained the same run to run. The change you made was a simple one, ion source versus two in operation. Now to noodle out what made the difference in and amongst a complex plasma environment that is known to be problematic.

Richard Hull

Aside: Image below...The poor boxed kitty cat's state of existence remains unknown to our senses solely due to the quantum uncertainty and probability related to the random radioactive decay of a radio-nuclide which will or will not release a poison into his food. Poor Kit-Kat. Is it any wonder he plans his revenge should he survive once his state is fully determined when the box is opened. Schrodinger will be clawed to death or not, again, based on the Quantum decay probability of that same radionuclide in the box with his kit-kat.
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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: Colliding beam mystery

Post by Rich Gorski »

Love the Schrodinger's cat photo. Haven't seen that one. I have a golden retriever so there's no cats around. However Augie (the dog) gave up on chasing squirrels so there's plenty of those around here tearing up the garden. Maybe we can put a few of those in the box. :)
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Re: Colliding beam mystery

Post by Richard Hull »

The squirrel to dog capture cross section is apparently rather low. Lots of squirrels, one dog. Really low capture cross section. I fear only a limited quantum tunneling possibility here. Putting the squirrels in a Schrodinger box, live or dead, your garden is safe as long as they are in the box. Nothing for the dog to capture.

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: Colliding beam mystery

Post by Peter Schmelcher »

Rich as a sanity test it might be interesting to run both A and B pulses together but out of phase. Then reduce the time delay of B to increase the pulse overlap with A.
-Peter
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Re: Colliding beam mystery

Post by Rich Gorski »

Peter,

Thanks for your input on source with delay. At the moment I have only one pulse generator which is triggering both ion sources simultaneously. I'll look into adding a delay circuit to one of the ion sources.

Thanks,
Rich G.
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Re: Colliding beam mystery

Post by Rich Gorski »

Hi all,

I believe I have solved the mystery with the 12% drop in NPR with 2 ion sources as apposed to one. Something I totally forgot about...the voltage drop across the 100K ballast resistor. In all my work so far I've been relying on the negative kV voltage reading from the analog meter of my Spellman DXR3000 PSU. So I was going by the voltage (-35kV) before the resistor (without the drop). The difference in the drop between 10mA and 20mA current is 1000V. That means when I was running with 10mA the actual voltage on the accelerator grid was -34kV and with 20mA the actual voltage was -33kV.

Wouldn't you know it, that totally explains the 12% drop in NPR going from 34 to 33 kV due to the exponential change in fusion cross section. From my previous post showing the exponential relation between NPR and kVs the exponent is 0.128 from the Excel fitted equation to my counts per minute data. So here's the math showing the 12% drop.

31.4e^0.128x

Putting in 34kv we have 31.4e^0.128*34 = 2770 counts per minute.
and at 33kV we have 31.4^0.128*33 = 2438 CPM
That's (2770-2438)/2770 = 0.119. or 12% drop !!!

Wow, that's exactly what I measured. It was my error forgetting about the ballast resistor all along.

So back to redoing the test with an adjustment for the voltage drop or at least adding a high voltage divider to know the real voltage applied.

Rich G.

Ps. One of the ion sources stopped working so it will be a few days in the repair shop.
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Richard Hull
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Re: Colliding beam mystery

Post by Richard Hull »

Sometime it is the little simple things in the background that confound us and our results being thought due to some strange agent within the fusion plasma.

Good bit of detective work.

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: Colliding beam mystery

Post by Frank Sanns »

Not to mention 1+1 must always be at least a little less than 2 in the universe. lol
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: Colliding beam mystery

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Ha, I asked Schrodingers cat this question (I wasn't sure if it was alive or dead or maybe just an AI) but here's what it told me.

"1+1 = 2 only in the mathematical sense and only because we (humans) defined it that way in base 10. I would venture that 1+1 can never truly = 2 when counting things or measuring anything in the physical world. Even when counting electrons, does 1 electron + 1 electron = 2 electrons? I guess the answer will always be no because of all their associated properties which the Pauli exclusion principle says they can never be the same while they are in the process of being simultaneously counted."

Rich G... and some stray cat that walk by or was it an AI.
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Richard Hull
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Re: Colliding beam mystery

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Rich came here with his problem for advice and a number of scenarios were proffered in response. Such advice, "at range" , (physically removed from the issue), can help solve problems. However, after a lot of help from best "guesses", Rich dug in, as he was there, and solved his conundrum.

I am reminded of Mark Twain's adage. "Only one man alone is worth anything; two will start an argument and three or more will start a war."

Sometimes, self-reliance is all we have in this world. Our best friend and confidant is most often ourselves, and decisions and direction, be they good or bad, are often the result of our inner character.

Got a problem? Ask away! We just might be able to help....

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: Colliding beam mystery

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Yes, its the very process of formulating the question so others understand... and those generous individuals with their advice...the problem and solution begins to become clear and leads you (hopefully) to a solution.

Rich G.
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Re: Colliding beam mystery

Post by Rich Gorski »

Hi everyone,
Here’s the latest data and my conclusion on the colliding beam mystery where I measured a 12% drop in NPR when two ion sources were running in colliding beam mode versus the NPR sum of each running separately. My explanation for the 12% drop is due to an error in the setup by not taking the voltage drop across the 100K ballast resistor into account.

Five runs were completed at -35kV and correcting for the resistor voltage drop by adjusting the main PSU voltage according to the PSU current. Each run had a duration of 1 minute using a 25% duty cycle. One second on and three seconds off. Below is the neutron CPM values for each run.
Picture1.jpg

At this point it seems that the 12% drop in neutron CPM from my previous test was mainly due to the kV drop across the 100k ballast resistor. However there still seems to be a trend for lower fusion rate when both ion sources are energized together and in colliding beam mode. The difference is quite small at -2.4% on average so all this could simply be the accumulation of various measurement and set up errors. No further tests on the colliding beam issue are planned at this time.

Thanks for listening,

Rich G.
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Dennis P Brown
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Re: Colliding beam mystery

Post by Dennis P Brown »

Excellent work. Do realize you haven't done anywhere enough runs to have confidence in those values differing being significant. That is, the difference cannot be well attributed to a real issue with colliding beams vs. non-colliding. Certainly space charge issues are a bit of a wild card.
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Re: Colliding beam mystery

Post by Rich Gorski »

Dennis,

Yes, agreed. considering the low -2.4% value there's not enough statistics here to know if I detected something interesting colliding versus not colliding. However it was a bit of fun and I got to use my ring accelerator device to do something different. Future plans are to add a third ion source to the accelerator so the beam axes are a 120 degrees apart. I'm hoping this will be ready for first light in a week or two. I will probably look it this again with three ion sources and post results here if something interesting shows up. I think it will look pretty cool so expect a few photos.

Rich G.
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Re: Colliding beam mystery

Post by Dennis P Brown »

I look forward to your future work. Your current series of experiments has been both interesting and very well done.
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