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Re: Robert Dwyer Fusor Progress

Posted: Thu Dec 21, 2017 11:31 am
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.

Re: Robert Dwyer Fusor Progress

Posted: Thu Dec 21, 2017 2:33 pm
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.

Re: Robert Dwyer Fusor Progress

Posted: Thu Dec 21, 2017 10:41 pm
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 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

Re: Robert Dwyer Fusor Progress

Posted: Sun Dec 31, 2017 9:38 pm
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.

Re: Robert Dwyer Fusor Progress

Posted: Sat Jan 06, 2018 11:13 pm
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.

Re: Robert Dwyer Fusor Progress

Posted: Thu Mar 22, 2018 3:59 am
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.

Re: Robert Dwyer Fusor Progress

Posted: Fri Mar 23, 2018 4:52 pm
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

Re: Robert Dwyer Fusor Progress

Posted: Mon Mar 26, 2018 2:08 pm
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.