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Re: Robert Dwyer Fusor Progress

Posted: Fri Dec 08, 2017 4:38 am
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
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

I hope to do more runs this weekend, with hopefully better results as I get more experience in operating the device.

Re: Robert Dwyer Fusor Progress

Posted: Fri Dec 08, 2017 5:12 am
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

Re: Robert Dwyer Fusor Progress

Posted: Sat Dec 09, 2017 2:49 am
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.

Re: Robert Dwyer Fusor Progress

Posted: Sat Dec 09, 2017 7:05 am
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

Re: Robert Dwyer Fusor Progress

Posted: Sun Dec 10, 2017 2:37 am
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.

Re: Robert Dwyer Fusor Progress

Posted: Sun Dec 10, 2017 11:38 am
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.

Re: Robert Dwyer Fusor Progress

Posted: Sun Dec 10, 2017 8:42 pm
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

Re: Robert Dwyer Fusor Progress

Posted: Mon Dec 11, 2017 9:53 am
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.

Re: Robert Dwyer Fusor Progress

Posted: Thu Dec 21, 2017 2:28 am
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.

Re: Robert Dwyer Fusor Progress

Posted: Thu Dec 21, 2017 4:14 am
by Scott Moroch

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.