Robert Dwyer Fusor Progress

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Robert Dwyer
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Re: Robert Dwyer Fusor Progress

Post by Robert Dwyer »

Over the last two days, I fixed a few issues with fusor, including the Ludlum 12 detecting noise, and getting a new power supply.

First with the Ludlum. I figured out that the detector was seeing the noise due to a faulty BNC cable. As soon as the cable was switched and I brought the device back up to about 10kv, no counts were seen.

As for the new power supply, Carl Willis ended up lending me a 50kv 5mA Hipotronics power supply that he had apparently used with one of his old fusors, since I was having issues with the X-ray transformer. In order to use it, I did have to modify some old RG-8 high voltage cable and an Amphenol 259 connector, but that wasn't too difficult to do.

Here are pictures of the supply, and modified cable:
50KV 5mA Power Supply.
50KV 5mA Power Supply.
Inside of the Supply
Inside of the Supply
Modified RG-8
Modified RG-8
As of right now, this is what my whole setup looks like:
Fusor Setup
Fusor Setup

So once I got the HV system up and running, I decided to do tests with no deuterium, just an air plasma. I know that my gas line is a bit leaky after the needle valve, so without opening the Deuterium regulator, I have a controlled air leak. Did a run at about 5 microns going up to 30kv. No plasma was formed at those pressure, and the x-rays coming out of the port were being detected at about 50,000 CPM. The 177 is however, VERY noise susceptible. I ended up moving the pancake probe about 4 feet away from the fusor whilst it was running, and it was still seeing about 10,00cpm. I put it behind the 1/8" lead shielding around the moderator for the He3 tube, and it still saw about the same number of counts. It does tell me that there are x-rays present, but now I know not to any degree of accuracy. The Ludlum 12 However, during this time, barely saw any counts, which is good. This makes me believe that I have fixed the noise issue, and it was really the fault of the cable.

Now, at this point I decided to actually try to maintain a discharge of the air plasma, whilst raising the voltage. This proved to be.... difficult. It was much harder than I expected, I see why operating a fusor is described as an "art." It took a long time with me fiddling with the voltage, and pressure, to finally get above 15kv. After of 3 hours of operation, I finally was getting tired, and decided to call it a night.

This morning was when I decided to try my hand at fusion.

Fusion attempt #1 went as follows:

1.) Turned on the TC gauge.
2.) Started roughing pump.
3.) Waited for the chamber to pump down to about 4 microns.
4.) Turned on ludlum 177 w/ pancake probe
5.) Turned on main power supply, and raised voltage to 20KV. X-rays where seen, but no counts on the ludlum 12. After this, I turned the voltage back down.
6.) Opened ball valve to gas line. The pressure spiked, but quickly pumped down to 5 microns.
7.) Opened Deuterium Bottle, and regulated it down to 10 PSI
8.) Opened needle valve, raised the pressure to about 10 microns.
9.) Raised the voltage on the power supply to about 12kv. Current reading was about 1mA
10.) At this point I began playing with the voltage and pressure to try to (as Richard describe dit) "inch worm" my way up to fusion voltages. No counts were seen during this period until I hit about 20KV @ 1mA
11.) The Ludlum 12 began to click away, but few counts were seen (less than 100CPM), however, as I played with the voltage some more, I began to see higher count rates. The current rise to about 1.5mA but the voltage would drop to 15kv. Here was when I started to see more counts (maybe 500 CPM). Soon, when I started lowering the pressure and getting voltages at about 20-22kv @1mA I started to see significantly larger count rates (1,000-4,000 CPM). I messed with more parameters like pressure and voltage, and I noticed that as the voltage dropped to about 15kv, I was still seeing counts at about 1,000 CPM. At first I thought this was wrong, but I remembered that I do have He3 tube which is fairly sensitive, so I do not believe that it is impossible. Still these are very low neutron counts.

12.) When I started to get the hang of things, and started to hold about 20kv @1mA with a pressure of 15 microns, I saw the highest count rates. The ludlum went off scale, and I had to switch the scale. Here I saw about 10-20,000 CPM, but this was short lived as the pressure would begin to drop and I would have to fiddle witht he pressure, and voltage again. Eventually, I reached a peak voltage of 27kv at about 1.2 mA and here I saw (briefly) about 25-30,000 CPM. A few times the ludlum would, pulse higher, but that was never constant for more than a second.

So that was my first fusion run. Low current, and with that, low neutron counts. However, I definitely think that fusion was occurring. With this I would like to begin the review process for the neutron club. I know that everyone will have questions, and want me to do more runs. After I write this, I am going to do a run without the moderator, but lead shielding. I also am hoping to use a bubble dosimeter to have another form of detection showing that I have neutrons. This is however, very exciting! Over a year I have been working on this, and now the project is finally coming to completion, and hopefully I will be eventually able to do experiments with the neutrons (provided I get better numbers).


Also, I did film a video of myself in the middle of the run. Sadly my phone died so the video cut out before I got the 27kv. Still, I hope this can provide some insight into what was happening within the device. I also apologize if I am repetitive in the video, but I was very excited during the whole thing.

https://www.youtube.com/watch?v=CaHLsl8 ... e=youtu.be
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Dennis P Brown
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Re: Robert Dwyer Fusor Progress

Post by Dennis P Brown »

Your power levels appear rather low for such high counts - I do suspect that your best pressure with a smaller chamber is in the 15 micron range. As such, most likely you are getting some fusion and maybe the detector is also picking up noise and neutrons - now just compare with and without a moderator and you can very likely distinguish between the issues.

Of course, the bubble detector is the gold standard (as long as it isn't over heated - now that must have been depressing for those it happen to.)

You have a 50 kV 5 ma supply, but keep losing the high voltage at 5 microns - you should easily get more current at 20-25 kV; something seems amiss.
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Richard Hull
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Re: Robert Dwyer Fusor Progress

Post by Richard Hull »

Dennis hit the nail on the head here. A rush of high counts is virtually impossible at 20kv and 5 microns and 1.5ma Good counts typically start to occur only around 25 kv @ 6 microns or more and 8-10ma of current. Something is definitely amiss.

I am almost positive the issue envolves a mis-biasing of the corona tube, and or, discrimination issues. Quite possibly, both issues in combination are creating the high counts at such microscopic current levels.

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 »

So I did the test with just lead shielding around the tube, and no moderator, and I did end up seeing noise in the 1,000-5,000 CPM range, with pulses off scale. This made me suspect the counts I was getting even more. I ended up asking if Carl Willis if he could come over and help diagnose my detector issues.

When Carl arrived he began to inspect the tube, he noticed a few things. First, that I was using a cable that was different (longer) than what the tube was calibrated with, and he said that may give false readings. Also, some of the BNC connections were dirty, so we cleaned them out with methanol. He eventually noticed that one of the main BNC connections on the tube was coming off. At 1400V this was causing corona discharge that , unless the connector was at a certain position, cause extremely high counts, without the fusor even being on. However, after fixing the detector to the best we could at the time, and putting it at an (awkward) position, where it wouldn't give any extremely high counts (from the broken BNC connection at least), we began to turn on the fusor once again, and it the counts we saw told a different story than before.

The system was pumped down to about 4 microns, deuterium was added, pressure rose to about 15 microns, and we began to turn up the voltage. After playing with the plasma a bit, we eventually got a stable discharge, along with neutron counts of 200-350 CPM around 15KV 1.5mA and a pressure of about 100 microns. This makes a lot more sense at these low power levels. Carl agreed that it made much more sense than what I was seeing before.

After this, we decided to try running at higher power. A 50W light bulb was being used as ballast, and that is why higher currents were not being seen. Carl and I replaced the bulb with a 20 Amp fuse (making sure to be careful whilst running with that in). However, the run did not produce and fusion. This was due to a solder joint that I had to hold the grid in place. Flux from the solder ended up getting to hot, outgassing, and burned up/spoiled the vacuum. Before this happened, we did get to see a a very beautiful star mode at 4kv. Carl also did say that I eventually will want to get another power supply that will be able to run higher currents, which I agree with.
4KV Nice Star Mode
4KV Nice Star Mode
Progress? Yes. We both believe there neutrons during the second run with 200-350 CPM, but sadly the detector started to succumb to noise during the high power run, and the vacuum feedthrough now needs cleaning. Carl also said he was going to work on repairing the detector connection while I work on cleaning the chamber, And re-orientating the fusor (viewport to the side, and the BeO) feedthrough coming from the bottom. Hopefully within the next week or two I can begin doing runs again, with a less noise susceptible detection system, and (ideally) bubble dosimeter readings.

Attached below are the links to two videos of when Carl Willis came later yesterday afternoon to help. The first is the run with 200-350 CPM, and the second is the high power run attempt. I do apologize for the second one cutting out a lot. My phone was running out of space and started acting weird. I eventually gave up on trying to record, but I hope it may provide some insight.

https://www.youtube.com/watch?v=OoqdWyWb7UU



https://www.youtube.com/watch?v=OoFkHW1g3Gc
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Richard Hull
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Re: Robert Dwyer Fusor Progress

Post by Richard Hull »

You have the extreme advantage of Carl's direct help. Pay close attention to what he says and does. You will learn a lot. I am sure you will have stable operation soon. All the best, of course, in your continued efforts.

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 »

Your system pressure for a run was at 100 microns?! Also, one should not have 15 kV and only get 1.5 ma at 100 microns unless your supply x-former is utterly saturated - which isn't very good news for this power supplies' usefulness if you want more current then this at any higher voltage.

I am not aware of anyone running a successful fusor at pressures that high (others may know more.) In any case, I do think your best performance will be in the 15 -20 micron range judging by your chamber size (very small - which has produced good results for some here.) For my x-former, any pressure above 10 - 15 microns results in a runaway current (over 100 ma! which is bad for my x-former.) My ballast resistor helps but isn't meant to handle such a conductive plasma. That is why I run around 5 microns like most do here; but my chamber is rather large.

What is your ballast resistor value?

Also, the color of your star mode appears to be using atm and not deuterium.

Fusor's are noise machines as I discovered and most who use detectors know only too well. Keep at the noise reduction and you will have success - just avoid issues like contamination in the chamber, which just makes running a stable system nearly impossible. Keep at it; progress can be slow and frustrating but once you get a clean signal, all this effort is so worth the trouble.

I am concerned that your overall power levels are very low for fusion - if you can get over 40 kV at 1.5 ma, that should be ok but 20-25 kV at 1.5 ma isn't going to make a significant fusion signal for most detector systems. That is, having a very small neutron signal makes all detection work very difficult; this also ups the requirements a great deal to achieve very low noise levels.

Aside: I discovered that ground loops were causing my detector system issues. So, I went to a battery supply (the detector system floats relative to ground) and this cleared up my last major noise issue relative to the fusor's plasma. This may not be relevant to you but keep it in mind.
Robert Dwyer
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Re: Robert Dwyer Fusor Progress

Post by Robert Dwyer »

It has been a while since I have posted anything on my fusor, because I have been waiting to get a bubble dosimeter to really show whether or not I had fusion. I knew that noise was being a serious issue for the He3 detector, so I thought a bubble dosimeter was the way to go. While I was waiting for the ones I ordered to come in, Carl Willis contacted me, and let me know he had one I could borrow. The one he lent me is a 20 bubbles/mrem dosimeter.
Bubble Dosimeter before the run
Bubble Dosimeter before the run
Before I did a fusion run, I wanted to make my gas delivery system easier to use, so I added a series of valves to restrict the flow more to add finer control. I added a shutoff valve right after the second ball valve on the regulator, and bellows valve to help throttle the flow before the needle valve.
Valves to be added.
Valves to be added.
New gas admission system
New gas admission system
So after a pump down of the system to about 4 microns, I began admitting the D2 to about 10 microns, and then turned on the power supply. I was using a 20 Amp fuse as a ballast for the supply this time, instead of the 50 watt light bulb, so I had more power, but it also meant I had to be a bit more careful in operation. I placed the bubble detector approximately 6cm away from the inner grid. The total run time was about 20 minutes, and I noticed the first 3 bubbles after about 15 minutes, when my voltage was at 27kv, my pressure at 32 microns, and my current at 4.5mA. In the next five minutes I pushed the voltage up farther to about 32kv @4mA with a pressure of about 25 microns, and saw two more bubbles.
Placement of the Bubble Dosimeter
Placement of the Bubble Dosimeter
Fusion Plasma
Fusion Plasma
Bubble Dosimter after the run
Bubble Dosimter after the run
Bubbles Dosimeter in different lighting
Bubbles Dosimeter in different lighting
\


This was extremely exciting to see! I want to do more runs with this detector, but I think this shows that I definately have neutrons. I want to get a bit more data before trying to turn this into a total neutrons/second. With this data I would like to ask to be considered for the neutron club again.
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Dennis P Brown
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Re: Robert Dwyer Fusor Progress

Post by Dennis P Brown »

Glad your efforts are starting to pay off!

I will leave the bubble detector results for those familiar with those types of detectors but certainly, those results look very promising.

Also, your fusor's pressures, voltages and currents sound very good and correct compared to similar systems previously posted - this also demonstrates that your fusor is operating in the proper manner similar to other successful systems!

A side issue: I am concerned that your bubble detector is so close to the fusor's cathode section - do consider a heat shield (a single vertical piece of aluminum foil that is air spaced both sides: i.e. detector-foil- fusor) and be sure cooling air is flowing across the bubble detector to prevent a disaster; that wood block will prevent proper air flow around the detector and also, that wood can insulate the detector in a bad way! Remember, that fusor is going to become very hot over twenty minutes of operation and that detector is sensitive to radiate heat, too.

My main question and I am confused by in your post is: Exactly what is a 20 amp fuse ballast? A fuse has essentially next to no resistance and a ballast for a fusor should, if memory serves, be over 50,000 ohms or so (and be high wattage; this ohm value, as I understand can cover a range.)

Finally, thanks for the pictures and your setup looks very good. Hope the neutron results are conclusive!
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Richard Hull
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Re: Robert Dwyer Fusor Progress

Post by Richard Hull »

The bubbles tell the story and the gear looks capable along with a well documented and progressing back story. I will log your name into the Neutron club. Keep us advised of future efforts with your fusor.

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 »

Thank you very much! I am honored. It has been a long, but fun journey over the last year and a half of trial-and error, struggling, and most importantly, learning. I will make sure to keep you all updated on further progress I make.

AS for questions on how I am ballasting, right now it is just a screw in 20 Amp fuse in place of the 50W light bulb that was being used as an inductive ballast that kept me from reaching the higher power levels I needed. I can see when I am operating that the device that the current will keep increasing as time goes on, so it it means more care must be taken in operation. It isn't ideal, and I do plan on replacing it soon.
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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.
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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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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"
-Albert Einstein
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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.
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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.
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