First Fusion for Liam David - Neutron Club Application

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Liam David
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First Fusion for Liam David - Neutron Club Application

Post by Liam David »

Today, December 25, 2016, I ran my fusor with deuterium for the first time and I believe that I have achieved fusion. I have documented my progress semi-regularly on the forums for the past few years, mostly in the images du jour section, but I'll give an overview of my system before I discuss the runs. Before I continue, I would like to note that very little fusion took place, and that both the length of the runs and the data collection were limited by problems with the power supply. More on that below.

The main chamber is a 2.75" conflat six-way cross coupled to a 2.75" tee and Pfeiffer PKR261 full range vacuum gauge. One viewport is located on the front of the tee, and the viewport with the camera is located on top. The high voltage feedthrough is based on Andrew Seltzman's design and consists of four nested alumina rods, a compression to 2.75" conflat fitting, and a Swagelok cap with teflon ferrules. The outer tube has a diameter of 0.75", and that is stepped down to a four bore rod which holds the grid wires in place. For the fusion runs, I covered the entire chamber in a lead vest.

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The vacuum system consists of your average two stage refrigeration pump which can pull the chamber down to about 20mtorr (~40mtorr on the convectron gauge since it's out of calibration compared to the PRK261). A Pfeiffer TPU-040 turbomolecular pump pulls the chamber down to 3e-6 torr. Outgassing appears to be the major leak source, as the pressure tends to follow a logarithmic curve over time when isolated from the pumps.

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The deuterium system uses a PEM cell from one of those Hydrostik charging stations and a needle valve. The drying tube, which consists of a tube filled with drierite, was bypassed due to various problems finding the right fittings, etc..., and the deuterium from the PEM cell was fed directly into the chamber.

Image

I bought one of the famous Spellman power supplies that showed up on eBay a few weeks ago. It is capable of 70kV and 8.56mA max at any voltage. I built a small control box with panel meters and knobs to control and monitor the supply over its local control port.

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Finally, the neutron detector is a 12" He-3 tube from the eBay seller cgroat3573 coupled to a Ludlum Model 12 ratemeter. The tube is encased in about 2" of paraffin wax. I adjusted the discriminator against a gamma check source, so any counts should be neutrons or weird high energy cosmic stuff. I also conducted a null test without deuterium in the chamber, and the detector is unaffected by plasma discharges or arcs. The pulses of plasma forming and extinguishing made my multimeters and gauges occasionally go crazy, but the radiation detection instruments were unaffected. The tube is pressed right up against the chamber as close to the center as possible.

Image

The Data
Background counts for the detectors are as follows:
Ludlum Model 3 pressed against the viewport and used to monitor the presence of x-rays: ~100cpm
Ludlum Model 26 used to monitor x-ray leakage: ~40-60cpm
Model 12 with He-3 tube: ~90cpm

During the runs, the pressure was between 5mtorr and 35mtorr, and usually about 15mtorr. The voltage was all over the place, but the neutron counts were observed above ~15kV and the current was always above 5mA. The maximum voltage reached was 35kV for a very short amount of time. The problems arose with a combination of two factors: the power supply and the pressure. First, I could not get the pressure to stabilize, regardless of how much I fiddled with the needle valve and turbo pump throttling valve. This caused the current draw at any given voltage to fluctuate, and since the Spellman supply automatically shuts off above 8.56mA, the supply constantly tripped when the pressure rose even slightly. Additionally, the supply treats the plasma as an an arc when it establishes, so combined with the constantly changing pressure, plasma forms and then extinguishes several times within seconds and shuts off the supply. I could not get precise numbers for the voltage and current, but here is the best data that I received:

Ludlum Model 3: off the chart at over 500kcpm at any voltage over 10kV
Model 26: Nothing above background anywhere on the shielded side
Model 12 with He-3 tube: The best runs were 5000cpm, 4500cpm, and 2000cpm, at about 20kV, 15kV, and 14kV respectively. The current rose from under 1mA to over 8.56mA when the supply shut off.
Edit: Here is the video: https://youtu.be/v04QdYwn8Fs I hope it will suffice as evidence.

With this, I would like to apply for the neutron club!


I have several more runs planned for the next week, so hopefully I'll get better data with more experience and feedback from this forum. As with any neutron club application, feel free to ask questions or criticize.

-Liam David
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Richard Hull
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Re: First Fusion for Liam David - Neutron Club Application

Post by Richard Hull »

Liam, a decent and honest report. I conditionally accept your results. (see my new conditional status addition to the rules for the neutrons club)


viewtopic.php?f=24&t=3134


You absolutely must have both a relatively stable pressure, voltage and current to make a viable run. You have far too much slop racing all through your system on every single avenue! There are wild pressure, voltage and current excursions, etc.

Focus now on stability and getting a stable voltage, current and pressure of about 25 kv at 5ma + and 8-10 microns of D2. Get some operational experience and tie down those wild excursions. Having a power supply that regularly shuts down at 8 ma is just as good as having no supply at all. All of this is due to a highly unstable gas pressure wanting to gulp more current than your supply can or will handle without shutting down.

You have good detection gear! Give it a break and allow it to do the good work it is capable of; obtain some stable operation.

Run some more tests that are stable and run the system with moderator and without moderator and report your reselts.

Richard Hull
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Re: First Fusion for Liam David - Neutron Club Application

Post by John Futter »

Liam
I do not see your HV ballast resistor in any of the shots
What value is it as this has plasma stability considerations ???
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Re: First Fusion for Liam David - Neutron Club Application

Post by Andrew Seltzman »

Liam,

Try to compare the count rates with the tube in the moderator and with the moderator removed, that will give you an additional point of reference to demonstrate that the counts are neutrons and not electrical noise.

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Re: First Fusion for Liam David - Neutron Club Application

Post by Liam David »

I did not have a ballast resistor in the first runs, but I will use a 60k resistor in my next attempt. Kinda sorta forgot it.... I am almost done with a mains frequency 50kV x-ray supply which will allow me to push the fusor to the limits without having an electronic unit shut off on me, so I'll probably use that supply next.

Andrew, on your more recent runs with the same Spellman supply, how were you able to keep the current at the 8.56mA limit? Did you use constant current mode, or are you doing something over Ethernet control?

I will work on establishing a constant pressure. The believe that the main part of the problem is balancing the PEM cell gas production with the flow rate through the fusor. The PEM cell builds pressure in the reservoir which increases the flow rate through the needle valve, causing the current to spike. This should be less of an issue with the new supply, but still an important factor.

Finally, I will do a moderator removal test once I reach a stable operating point. With an air plasma test the counter did not seem to pick up any interference, but one can never be too sure with these things. I might try to activate some indium foil if I get a decent number of counts, but the fusion rate will probably be far too low to detect anything using that method.

Thank you everyone for your feedback!
-Liam David
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Re: First Fusion for Liam David - Neutron Club Application

Post by Andrew Seltzman »

I was running my supply at the max output by tuning the pressure and ion source current to stably operate at the max current point. The supply has a little overhead over 8.56mA before it trips(but no constant current mode), so I tuned up to ~8.56mA for my runs. Mainly I attribute my success to the automatic pressure control, which allows the fusor to hold constant pressure with feedback from the vacuum gauge, and the ion sources that can be tuned for varying grid current at a constant current/pressure point. Without some manner of ionization(source,filament,etc) the plasma tends to be a little unstable in the <10mTorr range.

By the way, I don't see a grounding connection from the ground stud of the spellman supply to the fusor shell, adding this will improve system safety(as the ground through the AC lines can sometimes be a little iffy) and possibly decrease the noise you are experiencing on the multimeters and vacuum gauges(lower impedance ground then through the AC mains).
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Liam David
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Re: First Fusion for Liam David - Neutron Club Application

Post by Liam David »

I have the Spellman supply, chamber, and cart all grounded to a central port and then a grounding rod stuck eight feet in the dirt outside. Based on some more testing I did today, I believe that the counts I received yesterday were electrical noise. I will have to do a lot more testing and improve the power supply before I can definitively claim fusion.
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Re: First Fusion for Liam David - Neutron Club Application

Post by Rex Allers »

I agree with other replies that the first thing should be to work on getting pressure and voltage stable. Here are some other thoughts after looking at your post.

1) What is the internal dimension of your chamber? I think you said it is a 2.75" CF 6-way. From looking at stuff here, I think that would be about 1.35" ID. I think others have tried to do fusion in a chamber that small but I can't recall reading one that produced convincing data of a fusion run. Maybe the small size is part of the difficulty in keeping pressure stable.

2) You showed a fair amount about the HV feed-through but I didn't see a picture or description of your cathode grid. It seems to me that a grid design for such a small chamber could matter a lot.

3) You said you have a view port and a camera but I saw no picture of the plasma. Your pictures didn't even show, externally, what this port looks like.

4) For your D2 source, it looks like you have dismembered a Horizon Hydrofill unit. That seems a shame to me. They are getting hard to find now but if you do, they are typically over $300. From my hacking, I think that PEM cell you are using can make H or D at pressures well over 300 psi. The smaller plastic PEM cells that most have used for this can be bought new for about $40.

From the pictures, I think you may be running the cell directly from the 12 V supply. I haven't yet measured my Hydrofill in operation. (I intend to, and post information here on the forum when I gather data.) The electronics board of the Hydrofill has a switching regulator that I am guessing probably drives the cell at around 3 - 5 VDC. I think that running the cell at 12 V could kill that very nice high-pressure-capable unit.

You seem to have a pretty small rigid metal reservoir for your D2. I would think the pressure of your stored D2 could vary wildly, especially with the PEM cell you are using. I think something like the oil-displacement or Mylar balloon, that Rich and I have discussed, would be much better. Keeps the D2 at about steady atmospheric pressure and gives you a visual indication of the amount of D2 you have available.

Do you have some procedure for evacuating your D2 plumbing before generating D2? I would think you want a way to get rid of air so you have a consistent D2 purity.

You seem to have a lot of pretty big tubing between your needle valve and the chamber. I don't know if this would affect operation but I think I would like less volume in this feed plumbing, especially with such a small chamber.

5) Once you get pressure and voltage stable over a couple runs, I think the normal way to show your neutron detector is working is to make a run with the moderator around the detector tube and another run with no moderator. If you did that, I missed it.


-- One other minor comment, that is just my opinion. The pictures in your post are all links to Photobucket. They show up fine but are transient if the photobucket source ever goes away. I often like to open pics in a local viewer so I can zoom in or out. When I first tried that yesterday I had a problem opening some of them that way. Today they all seem to open fine, so not sure what happened.

Anyway, especially for a post that is documenting something, I think I would prefer to see the images uploaded to the forum space.

-- I have been lurking here for years and have never even assembled a demo fusor, so I do applaud you for doing something real. I have only separately tried parts of what I will need to put together. I hope I get to a real try soon. My comments may verge on Monday morning quarterbacking but, I think your set-up could use some improvements to convince that fusion is really happening.
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Re: First Fusion for Liam David - Neutron Club Application

Post by Dennis P Brown »

I too discovered that getting a stable voltage/current in a fusor can be an issue at first. First off, getting my system down to 10-5 torr helps; as well as a short purge using deuterium gas under a 10 - 12 kV plasma at 10 microns (I can get high currents but I don't think that is necessary.) My system uses a diffusion pump and only a gate valve (no cold trap.)

After this, I noticed my fusor worked better but still had issues.

Then after a dozen or so such runs my fusor became highly stable and was a snap to run at 6 - 10 microns and select any voltage/current I desired. I assume that the chamber was acting up due to impurities and these burned away with usage.

After this, the key to steady plasma/voltage/current behavior was pressure control - both via the gate valve and then, by careful and very fine control of deuterium leak rate into the system.

Of course, these are just my results and may not be relevant to your system.

Aside: you didn't say anything about a master gate valve between the turbo and your chamber. If the turbo is running full on the system and you are trying to control pressure via a not to precise needle valve - not going to work very well. I use a high end micro-needle valve and a gate valve on the DP - this gives me very precise pressure control and that provides extremely stable voltage/current in my fusor (when clean.) In fact, I control my fusor's current to a few milli-amps by very tiny changes in the needle valve once I set my gate valve (which controls my gross voltage.)
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Re: First Fusion for Liam David - Neutron Club Application

Post by Rich Feldman »

Yes on what the other guys said.

Just one minor bone to pick, and that's the recommendation for a gate valve between chamber and pump. The term "gate valve" goes with one particular valve style. It's not about how, where, or why the valve is installed in a system.

Reading fusor.net has taught me the apparent virtue of a continuously adjustable throttle between chamber and pump. Could be a gate valve, butterfly valve, conductance controller, etc. Doesn't need to be closable down to zero flow, or to physically withstand more than tiny amounts of differential pressure. There's a pretty comprehensive listing here: http://www.lesker.com/newweb/valves/val ... cfm?pgid=0
including this gem, which might have been written for fusors:
cc.PNG
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Liam David
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Re: First Fusion for Liam David - Neutron Club Application

Post by Liam David »

I have a 2.75" butterfly valve between the turbo and chamber and I always throttle the pump before introducing deuterium. It does wonders for gas usage.
Dennis, what is the Cv for the needle valve you're using?
I use one with a 0.05Cv (I think the rating is for water, but I'm not too sure), which works OK, but relatively small adjustments do make a significant difference and it can be challenging to get the pressure stable. I have run the fusor several times, both with and without deuterium, and thus I don't think contamination is a problem for my system. Additionally, I can get to 2e-6 torr after about an hour of pumping and the chamber rises to less than 100mtorr after two days and then flattens off, indicating that outgassing or virtual leaks are the only leak sources.
I will try your method of setting the voltage and then adjusting the pressure to establish plasma and control the whole thing. Perhaps it will give me better stability and reduce gas consumption.

In response to Rex's questions and comments:

1. The chamber is a 2.75" conflat 6-way cross, which yields a cavity in the center about 1.9" in diameter. Although such small chambers never reach the mega neutron mark, several members of this forum have demonstrated fusion in a similarly sized chamber, notably Scott and Jack just a few months ago with a KF-50 cross.

2. I'll be posting some more pictures soon, presumably with my next claim. The inner grid is about 1cm in diameter and is composed of two tungsten loops with a wire diameter of 0.25mm.

3. Yes, I should have taken updated pictures before adding the lead vest, but I do have some reasonably up-to-date pictures in my other progress posts. I will definitely take more time in describing my system and adding pictures with my next report.

4. The rigid metal tube is a drierite gas dryer and is definitely not large enough for a reservoir. I borrowed the Hydrofill unit from my school, which just happened to have several laying around unused. I didn't break anything, and I can easily reassemble it for full functionality. I have built a small oil displacement reservoir using two test tubes to replace the hydrostik system. It works OK, but the gas is used up a little to quickly for extended operation which would help in stabilizing everything. Of course I flushed the system several times with deuterium to ensure purity.

5. I have done a few runs where I removed the moderator, but since I have problems reaching stable operation, I can't use this as evidence yet, especially since removing the tube from the moderator causes the counter to jump...

Thank you for the feedback everyone. Progress will be a little slower now that school has resumed, but I should be posting more results within the next month or so in accordance with Richard's new conditional acceptance policy.
-Liam David
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Re: First Fusion for Liam David - Neutron Club Application

Post by Richard Hull »

You are slowly learning that if you think making a fusor is a chore, learning to operate it is an art form. Money can't buy or instill artifice. I have written to this point extensively.

Doing fusion is not about building a fusor, it is all about knowing how to make it work.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: First Fusion for Liam David - Neutron Club Application

Post by Scott Moroch »

Liam,

Having been down this road with a small fusor I think I can provide some advice. I happen to very much agree with Richard when he says that doing fusion is not just building a fusor. In other words, assembling a vacuum chamber, diffusion pump, gas line, Hv, etc with quality gear does not guarantee that the system is going to produce 1e5-1e6 n/s. For example, it seems to me that sometimes that people tend to purchase very large, fancy diffusion pumps for their systems. In reality, I think that you want the smallest diffusion pump possible. Although it will take longer to pump the entire system down initially, you will be thankful when you try to feed D2 in and stabilize the pressure. One method of course is to seriously throttle down the vacuum system, but this is not always too easy with a smaller system.

In terms of your specific fusor, my first bit of advice is to do everything you can to regulate your vacuum and gas flow. This may require adding an additional throttling valve to your vacuum system, which perhaps you are not prepared to add as of yet. In our KF 50 system we had a 285 l/s diffusion pump (complete overkill, hence my point above) with a 3" throat. This was cut down to KF 16 (~.7") with a throttle valve and a butterfly valve.

A less expensive, quicker solution would be to do everything you can to regulate the gas flow. When we ran the KF 50 chamber we only had a fine metering valve. The valve we used was a Swagelok ss-ss4 needle valve (the finest control valve swagelok makes at 0.004 Cv) and this was not sufficient. With our larger system we had a diffusion pump with a much smaller pumping speed + a throttling valve and an MFC for gas control. If I were to go back to the KF 50 system, I would use the ss-ss4 needle valve, 1/16" capillary tubing and potentially look into a needle orifice. Once you are able to stabilize the pressure in the chamber and maintain a state of equilibrium, everything else will be significantly easier.

Our gas control was very poor in our KF 50 cross but we managed to detect fusion by backfilling the chamber to 40-50mTorr of D2 and slowly bringing down the chamber with the vacuum system. On the contrary, in Fusor II we throttled down the vacuum system first and then slowly inserted D2. This allowed us to basically choose any pressure we wanted and maintain equilibrium at that point. Although this is a bit more difficult in a smaller Cf 2.75" chamber, it is certainly possible.

After that has been resolved, the other issues will be minor. Try your best to keep your grid on the smaller size (i think ours was .3") and relatively symmetrical. We tried the double and single loop, with the single loop being easier to make and install.

Although some of these changes may not be simple, easy, and cheap, some of them can be added to the system for a fairly low cost (capillary tubing, finer metering valve, etc) with ebay.

Let me know if you have any questions and certainly feel free to reach out to me. Best of luck.

Scott Moroch
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Re: First Fusion for Liam David - Neutron Club Application

Post by Dennis P Brown »

Scott offers a lot of good advice; relative to my needle valve flow rate, it too is a Swagelok unit and I need four and a half turns to get into the range where my fusor pressure is effected - then +/- half a turn creates very strong changes in my system pressure.

Relative to my fusor, closing the gate valve (and waiting for my pressure to just start to rise) and then barely opening it is how I start up my system after flushing and plasma cleaning the fusor first. My D2 control valve is a high end unit so I assume it is similar to Scott's but being a surplus, ebay unit, no idea for its parameters. I get my gas from a lecture bottle of highly pure D2. That, I am certain, also helps with stability of my fusor.
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Re: First Fusion for Liam David - Neutron Club Application

Post by Richard Hull »

I have never felt, nor have I ever seen, absolutely convincing data related to purity effects of Deuterium admitted into a fusor. As long as the impurity admitted with D2 is only H2 I would think there would be little or not detectable difference between 95% D2 and 99.99% D2 in and amateur fusor device. Water, as an impurity, is another matter and all effort directed at reducing this impurity in any electrolysis of heavy water is a positive thing.

Junk 98-99% D2 is just perfect for the fusor. Anything better had better be a free bottle found lying around a lab or come from some very deep money pockets.

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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