Robert Dwyer Fusor Progress

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Robert Dwyer
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Re: Robert Dwyer Fusor Progress

Post by Robert Dwyer »

After about a month, I finally find myself back on the forums ready to report on more progress with my fusor. I have not been able to work too much on it in the last few weeks, because many scholarship application deadlines were due.

After my last post, I had tried a few more runs running at less than 30kv, but none of them yielded too many interesting results. My power supply is capable of 50kv, and I decided that it might be good to invest in some lead shielding to run it at the higher powers.

After the purchasing of the lead shielding, I ran into a major problem trying to run at voltages higher than 35v, arcing. Apparently my insulator bust have been dirty, because arcs were tracking along the ceramic to the vacuum chamber. After cleaning the insulator, I decided to move the fusor so that the HV feedthrough was pointing down, and I could submerge the conductor in oil, to prevent any tracking occurring. It is not exactly the best looking fusor, since It is riddled in lead sheet and duct tape, but it works. Once this was finished, I was ready to try my hand at fusion again.
Latest picture of the fusor
Latest picture of the fusor
The latest run I did was at the following parameters:

Max Voltage: 45kv
Max Current 4.5ma
Pressure: 60-70 microns
Run Time: 12 minutes

I positioned my bubble detector about 7cm from the center of the vacuum chamber. After twelve minutes I had 46 bubbles on my 20 bub/mrem dosimeter. A major improvement. I am hoping to do more runs with my less sensitive dosimeter (easier counting), and try a higher current power supply, to try and increase my fusion numbers.
Bubble dosimeter after latest run
Bubble dosimeter after latest run

I hope to do more runs this weekend, with hopefully better results as I get more experience in operating the device.
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Richard Hull
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Re: Robert Dwyer Fusor Progress

Post by Richard Hull »

Thanks for the report on your latest efforts. Nice work and remember, once you do fusion, practice makes perfect. You do better each time.

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
Robert Dwyer
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Re: Robert Dwyer Fusor Progress

Post by Robert Dwyer »

Did another run when I got home tonight, but this time using my 13 bubbles/mrem detector, and I reconfigured the lead shielding slightly, so I could place it closer to the source (6cm).

I ran the fusor for 5 minutes, with a max voltage of 48kv and a current of 4.7ma. The result was 33 bubbles.

I believe this means that at 6cm from the source there is about 30mrem/hr of neutron radiation, and that corresponds to about 860,000 n/s! I am much closer to the million n/s mark I am trying to hit!

If I made an error in these calculations, someone please let me know. I am hoping to do another 5 minute run tomorrow to hopefully repeat these values.
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Richard Hull
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Re: Robert Dwyer Fusor Progress

Post by Richard Hull »

Your figures sound about right. However, voltage and current are just part of what you should be reporting. You need to always quote the pressure of the flowing D2. (time of run- precise, pressure- avg., voltage- avg., current- avg.)....Most all fusors working at their maximum will have small voltage and current transients during the run. A few might even see a pressure change. In all cases, good electronic counts and bubble count over the timed period will rather under-estimate your many peak emission rates and over estimate the full run's average emission rate. Regardless, all of this data is better than a poke in the eye with a sharp stick.

With a bubble dosimeter, for calculation purposes, you need to get the fusor more or less near you optimum run point, then put the dosimeter near the fusor at a suitable fixed range, do a timed run and then count your bubbles. Finally, do the math from there to find isotropic neutron emission rate.

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
Robert Dwyer
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Re: Robert Dwyer Fusor Progress

Post by Robert Dwyer »

Sorry for forgetting the pressure. That run, the plasma was lite at 60 microns, but my stable pressure was at 55 microns.

I did that second run with the 13 bubble/mrem detector tonight. The parameters were:

Voltage: 49kv
Current 4.5ma
Pressure: 50 microns
Run Time: 3 minutes

Instead of taking the time over the whole run (once the plasma is first lit, and has ended), I decided to get a stable plasma at the 49kv 4.5ma parameters I wanted, uncompressed the detector, and set a timer for three minutes. This way I would get a more accurate n/s.

I got 25 bubbles in a 3 minute period of time, which corresponds to about 1.1e^6 n/s! I finally hit that mega neutron mark! With these numbers I think I am going to start work on a neutron oven so I can do some activation experiments.
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Dennis P Brown
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Re: Robert Dwyer Fusor Progress

Post by Dennis P Brown »

Your pressure appears rather high - at 50 microns, your ionized gas would appear as an almost open short, I'd think. Maybe your gauge isn't accurate?

Also, I am rather surprised that 220 watts of power can deliver over a million neutrons; has anyone ever before reached such neutron levels at such low power power? Maybe this has something to do with your pressure/design or is such high rates normal for 50 kV and low power?

In any case, activation should differently be your next step.

Regardless, your neutron level via the bubble detector is impressive and activation should be very easy. Your having Pb shielding between the fusor and bubble detector is an excellent idea since that will readily protect the detector from any radiated heat.
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Richard Hull
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Re: Robert Dwyer Fusor Progress

Post by Richard Hull »

Actually his pressure might not be high. It depends on his gauge, of course, but we have seen 100% of these small cross chambers running at unheard of pressures. They seem to be extremely successful which assembled well and once the operator get his "sea legs" in operating his fusor. I am just about tempted to kill fusor IV and go with the 6 way cross I obtained at HEAS 2017. A simple 4 way cross would save two blank-offs, however.

With recent reports on smaller cross chambers, the new norm in rapid success might spell the end for the larger cylindrical and spherical fusors. Thus fusors in the future might not be quite as impressive looking. These smaller systems look like a plumbing nightmare under the kitchen sink. However, they are working and working well at higher pressures and getting results at lower voltages due to the large fusion fuel pressures.

The new norm might just take on the form of an amateur fusioneer's law "The Fusor Criteria" a modified form of the Lawson criteria strictly for IEC fusors! Dare I coin this new term within the community?

The fusor Criteria - Produce the smallest possible containment vessel, use the highest feasible deuterium pressure and the highest voltage and current obtainable within the arc over limitation of the construction.

What really are the limits? I think we are "pecking at the lobes", (old radar term), of a scenario for optimal operation while working at lower cost assemblies. Anyone want to try a "nano-fusor"

Another question? Compare the mean free path in a 6" fusor for deuterons at 10-15 microns with that of a 1.5" fusor, (Inside of a 2.75 CF cross), at 40- 50 microns. This could be the deciding factor in why we are so improved in smaller devices...

Wow! A lot to think over. I feel like a new FAQ in the construction forum.

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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Dennis P Brown
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Re: Robert Dwyer Fusor Progress

Post by Dennis P Brown »

I will say this, putting a screen in the form of a cylinder (acting as an anode) in my large fusor chamber, which enabled (really, forced) my fusor to operate at almost three times its previous operating pressure - effectively reducing my fusor volume as 'seen' by my cathode; hence, my probability of collisions certainly increased compared to the previous larger volume/lower pressure. That is, I went from 4 to 5 microns to 14 - 15 microns operating pressure while my voltage remained 31/32 kV and current could be set from 26 - 42 ma depending on small pressure changes; those power parameters stayed the same. This trival change certainly impacted my operating pressure even through, my real fusor volume was unchanged - only the volume 'seen' by the cathode relative to this new anode was what is changed in my fusor.

My screen is stainless steel with 1 cm square grid size.

So it is possible that a large fusor can be made to operate like a small one simply by adding a screen anode around the cathode in the large volume chamber.

I do agree that the smaller chambers merit more detailed study - all I did was place a small diameter cylinder shaped open screen and my operating pressure increased by nearly a factor of three. If only I could get my neutron counter to work again, I'd be able to compare neutron 'flux' rate changes for these two configurations. That is why I returned to the issue of my burned out ST-360 and trying to build a lower noise power supply for my detector.

But Richard, you have to agree that 1.1 million neutrons with just 220 watts wasn't something anyone would expect. That power level is, normally, the very low end of what most people consider usable power to generate a neutron flux that can be detected, much less reach near record levels of neutrons. I guess the next question is how low can one go - that is, both in power and size and create detectable fusion using std detectors?

Aside: modifying a fusor using a screen to increase its operating pressure comes at a cost: deuterium usage can be increased dramatically. While I do not have an electrode that can be attached to a small four way cross, so I will have to continue with using my large fusor/screen anode system for now, I would say to people building their first fusor to seriously consider using a four-way connector rather then any larger volume sphere like system.
Robert Dwyer
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Re: Robert Dwyer Fusor Progress

Post by Robert Dwyer »

It has been a few weeks since I last posted. I just finished finals and now that I am winter break, I plan to more with the fusor. I shooting to have an activation setup done by the end of January.

First however, I would like to discuss the results I had posted in my my last two posts. I was claiming to get 840,000 and then 1.1 million n/s. After Dennis' comment on how that was very high for the power I was putting in, I started to question my own results. After looking back on my calculations, I found that I had been looking at things on the scale of mrem/hr and neutrons/hr, and not seconds. After reviewing Richard's FAQ entitled "BTI Bubbles Detector Mathematics" I re-did the calculations, and they are as follows:

The results I got:

6cm from the source over a 3 minute period of time, I got 25 bubbles in a 13 bubble/mrem dosimeter.

Assuming the vacuum chamber is 1.5" in diameter and that the cathode is perfectly centered in the chamber, we are looking at a 785cm^2 surface area.

Over 1/20th of an hour I got 1.92mrem.

Doing the math :

20 x 8 x1.92 = 307 n/cm^2/sec at the detector. Multiplying this by the surface area we get: 785 * 307 = 240,995 n/s.

This is about a quarter of what I reported in my previous post.

2.4e^5 neutrons/sec isn't bad, but the mega mark I have been trying to hit. I apologize for the miscalculations. I still believe that the mega mark can be achieved (perhaps not with the 250w supply I have, but i am hoping to work on a higher power one), but first, more experiments must be done. I am also hoping to have indium activation to support any more claims.

For now however 1.1 million n/s with 220w is too good to be true.
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Scott Moroch
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Re: Robert Dwyer Fusor Progress

Post by Scott Moroch »

Robert,

Really great progress. You are doing great work in the area of small fusors. I would be really interested to see what measurements you get from a foot away with the Bubble Dosimeter. As we know, treating a fusor as a point source is not entirely accurate in close range because fusion occurs everywhere in the device (including the center through ion-ion collisions, between the grid and wall through ion-background collisions and Beam-on-Target on the wall).

As you move the detector further away the fusor will begin to behave as a point source which will give more accurate measurements of the Total Isotropic Emission Rate.

Scott
"In the middle of difficulty lies opportunity"
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Dennis P Brown
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Re: Robert Dwyer Fusor Progress

Post by Dennis P Brown »

It is very easy to make mistakes with neutron calculations; however, I do believe your newest calculation is fairly accurate. It is close to my value of 180 k/sec and while I was running just over 1200 watts I was using a much lower voltage (31 kV.) Voltage matters a good bit so your new value does appear consistent with my results (I made ten runs with a mod and average the rate.)

In any case, a straight forward method to confirm the million plus mark would be Ag activation, which should easily be detectable at that flux rate.
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Jim Kovalchick
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Re: Robert Dwyer Fusor Progress

Post by Jim Kovalchick »

Scott M is correct with his comments about taking care not to treat fusors as point sources when calculating neutron rates. The same care needs to be applied whether you have a large or small fusor. Taking readings at various distances will give a better understanding.
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Richard Hull
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Re: Robert Dwyer Fusor Progress

Post by Richard Hull »

Statistically, big numbers, be they bubbles or correct electronic counts, are better than small numbers. Ideally, all readings should be point source readings. Also, ideally this is impossible with a fusor. However, as noted, one can approach the ideal to a point that any extended detector size and source size will have lost a lot of error due to same.

Way back when the world was young and so was the Fusor.net site, we had a discussion on this very matter. Placing a bubble detector 6 feet from a 6" fusor would answer the statistical need for "point source" counting. However over 6 different 15 minute runs bubble counts of 1,1,2,1,3,2 would not really be a fun thing to hang your "statistical hat" on. Sometimes, in statistics one might be tempted to throw out the 3 as a flyer in a much larger "set", as the ones and twos are predominant. This would average out to 7/6 or 1.16. Figuring on 1.16 neutron bubbles you would get X for your isotropic emission. However, if you look at those 2's you would have almost 2X the actual neutron numbers and that lonely 3 would see 3X your isotropic emission. While this example is extreme, you see that the statistics are poor at this end, too. Small numbers in a small data set are not really a great analysis.

Most of the above older discussion revolved around those who sought to do pulsed fusion "way back when", (which they never did). It was felt that electronic counting would go afoul of the large area EMP near the device and that detection "at range" would be needed to rely on electronic counting methods. Furthermore, due to a limited repetition rate, close-in silver activation might not be possible. This line of thought is still viable for pulsed machines.

The upshot is that our numbers for continuous operating fusors, regardless of methodology, will always be incorrect to +/- 20-30%. This has been the assumption all along to those who have hung around long enough and had even a rudimentary toe dip in the "statistics pool".

As I have said all along, while the exact computed isotropic number may be off 30%, the run to run big count numbers of improvement or degradation of operation might be counted on to better than 5%, provided stable operation over the data collection periods by competent operators and well controlled fusors.

By keeping the runs long and the detectors close enough to attain decent numbers that appear to be, rather repeatable results, and you have a marginally acceptable set size, you can be assured that the statistics will put you in that 20-30% range.

These darned neutrons!..........They are so hard to count, being neutral and all that...............The detection efficiency is never great to start with.....Add to all of this, amateur and inexperienced hands......All of the foregoing coupled with limited funds for the best materials and detection methods and one gets to the point of near despair. We can only get so "nit picky" on neutron numbers.

What we do have is a decent long term idea of what wattage is needed to get certain results at certain voltages, currents and pressures in fusors of 4-8 inch size. This new cadre of 1.5 to 2-inch machines will have to make its way into a new data set, it seems.

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
Robert Dwyer
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Re: Robert Dwyer Fusor Progress

Post by Robert Dwyer »

I've been doing a few more runs and have found some interesting affects in the fusor. First I noticed that I could get the plasma to light at much mower pressures (10 microns) if I biased the cathode higher, to about 20kv instead of 15kv, before admitting the D2 gas. However, the plasma was wildly unstable and really could not stay lit for more than 30 seconds at this pressure. It would demand a very large increase to about 50kv in order to keep the plasma current at 1ma, but the current would quickly drop, and my supply only goes to 50kv. I found that I can run it at 25 microns fairly stable, but I am unsure as to how the fusion rates compare vs. pressure. Normally I was running at 40-50 microns. I want to try a few 5-10 minute runs at various pressures trying to keep the voltage and current around 45-50kv at 4.5ma.

In terms of neutron detection, I find that bubble dosimeters may not be the best to use right now. In the last week the temperature here dropped significantly. When I take the dosimeters out of their tubes in my house the temperature indicator is green, however within two minutes of being outside in my garage by the fusor, they turn black. This means I am outside the ideal operating range of the dosimeter. I believe the cold also means there is lower chance of the bubbles forming. The good news is that I have ordered the plastic and materials for an activation setup, and that should be here in the next few weeks. I am hoping to activate some silver, and perhaps some indium I have around, and compare the counts I get to results others have posted to infer a neutron rate. Another project is to fix a broken ludlum 12 I have and to try and use it with the Russian He3 tube I have laying around.

Lots of work to do! I will try to keep everyone updated on my progress.

Also, I ended up ordering two of the cheap Chinese precipitator supplies that had been brought up a little while ago. The ones I bought supposedly can get you 60kv at about 6.6ma. Dunno if this is true or not, but I thought it may be worth a shot to test them on my fusor. If they work it means I can crank out more voltage at slightly higher currents meaning more fusion. If they don't deliver the full power, then they still may be useful for another project in the future. Either way, it will be fun to test.
Robert Dwyer
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Re: Robert Dwyer Fusor Progress

Post by Robert Dwyer »

I did another run with the fusor today.
Pressure: 45 microns
Voltage: 47kv
Current 4.7mA
Data Collection Period: 3 minutes.
Dosimeter distance from the center: 18cm
Bubbles: 10

I calculated the total isotropic emission rate of 130,288 n/s from the fusor. It is definitely apparent how quickly the neutron flux drops off with distance. 32n/sqcm/sec at 18cm is pretty low.

I think I will try to take data at 12cm from the course with the dosimeter, and check those measurements against the 6cm and 18cm data.
Robert Dwyer
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Re: Robert Dwyer Fusor Progress

Post by Robert Dwyer »

Hello Everyone,

I have not posted in a while and I thought I might make an update on some of the latest news regarding my fusor.

First, I did 3 more runs at varying distances (16cm, 12cm, 10cm from source), and found the average output of my device to be 220,000 n/s when running at 50kv at 4.7ma with a background pressure of 45 microns of D2. This is not very much. Based on other peoples data I believe It is because I am either in an awkward voltage/current ratio area, or maybe my pressure is too high. I would like to try raising the voltage to 60kv or doubling the current, but that is just not possible with my current supply.

I also did a slight rebuild after I found a few areas where x-rays leaked from my fusor's shielding (especially around the Beryllium Oxide feedthrough). Included in the rebuilt is a series of 1" thich 7"x7" HDPE blocks I got a while back for an activation setup, but unless my neutron counts improve, I doubt I will be able to do much with it.

The new setup saves more space and looks better, but I have yet to test it, and I have not really had much more time to do more with the device. I have been fairly busy with school as graduation is quickly approaching. I am also finding myself spending more time in the Plasma Lab I work in as well (this is good as It means I am working on projects and getting more experience). Lastly, as a requirement for my high school in order to graduate, I am going to begin another part-time internship at a local company doing Dense Plasma Focus. It is a really cool place, and their device is amazing. They've got tons of various activation detectors, scintallators, and T.O.F. diagnostics for neutrons, which they say I will be helping set up and interpret data from. Although an excellent and exciting experience, It means there is less time for me to focus on home-based activities.

However, all is not lost for this fusor. About a month ago I got accepted as a pre-major in the nuclear engineering department at my local University. I was talking to a few faculty there, and it appears that there may be a chance that I can eventually move my device into a shielded room there where they have more equipment available.

Time will tell whether I will be able to more with my device. For the next few months however, I am sad to say that I may not be submitting any new information on my fusor.
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Richard Hull
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Re: Robert Dwyer Fusor Progress

Post by Richard Hull »

Robert, You have done better than most young folks here and have stuck with your system to do the best work possible within the limits of what is a new type of fusor system for us old boys. (ultra small chambers). The rather high pressure operation stunned us all.

Now to issues. We are to be reminded of what is needed to do fusion in our specific environment. (fusor)

1. Voltage needs to be of a certain level to push the probability, (cross section), of fusion higher and higher with voltage increase. You are doing great here assuming your voltage readings at the grid are correct! (high probability).

2. Amount of fusible gas is critical. More gas pressure means more fusible fuel in the fusor. (Again, superb amount of fuel in your system ready to burn)

3. The current is ultra critical. The current represents the number of ions, (hopefully, positive deuterons present), to enter into probable reactions. (here, you are rather low on current compared to the bigger systems)

I am not saying current is your issue, but it might be. The issue may also come down to mean free path. In the big fusors we operate at 1/4 your pressure meaning longer mean free path with 2 to 3 times the current. All of this is food for thought.

I will note that for those looking to just join the neutron club and do D-D fusion for the lowest dollar spent, the small conflat cross is the way to go. I think there is now enough evidence accumulated over the past two years to show that this is the case provided such system builders can prove they are doing fusion, which most have been able to do to our satisfaction.

All the very best in your future that now seems bright, indeed. It is always a pleasure to see the younger members here take a win in fusion to a probable career path via higher education. In these cases we are justified in a bit of pride in having , taught, mentored, cajoled, pushed and aided young minds to develop more skills and let their natural talent shine.

In a world that, to this old soul, is seeing a general dumb down of the population, as a whole, it is nice to note that the cream still tends to rise to the top in spite of many recent impediments to their doing so.

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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Dennis P Brown
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Re: Robert Dwyer Fusor Progress

Post by Dennis P Brown »

Robert, your results have been excellent and you should be proud of your success.

I also understand taking time off - I too am out of the game now (my very nice borrowed x-former needed to be returned to its owner (yes, they don't want to sell it to me and have a project they want to use it for.))

I can't complain at all since it got me neutrons and the person was very tolerant of my using it for almost two years (including the danger to the x-former if I ever happen to short the device - luckily, never had that happen.) I may or may not build another unit.

Hope you get time in the not too distant future to get back into the game. Best of luck.
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