Fusor Update - Liam David

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
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Richard Hull
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Re: Fusor Update - Liam David

Post by Richard Hull »

Great continuing work on your system. It seems there are always tweeks that we seem to find interesting to test out to better the performance. Good work and continued good luck in your 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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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

My 2nd Spellman supply gave up the ghost the other day, so now I'm limited to 8.56mA/600W again. One of the two flyback's secondaries got crispy causing the voltage and current to misbehave, especially in parallel with the other supply. Unfortunately it's very much a proprietary part and I don't have the ability to wind another. I believe it was end-of-life when I bought it and operating the fusor finally pushed it over the edge.

Flyback.jpg
Flyback 2.jpg

After years of use, I was finally forced to clean my chamber. The graphite grids I've been using have a habit of depositing on the walls, and after a particularly hot run the other day the coating began flaking and causing arcing. I scrubbed the inside with fine steel wool, used some vinegar to help loosen things up, rinsed with isopropyl, and baked it in the oven at 200C for a few hours. While not shiny like new, it's a lot better.

Deposition.jpg
Thick deposition flaking after intense heating.
Thick deposition flaking after intense heating.

The graphite grids were outgassing enough to limit long-term stability and letting the chamber sit overnight replenished the reservoir even after a thorough plasma bake. I made one from a 3/4" stainless pipe, with the added bonus of it not being super fragile. It turned nice and blue after heating up and there's a distinct ring on the inside as was also seen by Jon Rosenstiel. The ends also have darker bands.

Grid.jpg

There are two main limiting factors at the moment: symmetry and heating. The asymmetric discoloration on the two endcaps and just eyeballing were enough to confirm that the grid isn't quite coaxial nor centered. I 3D printed a new feedthrough aligner and a temporary jig that mounts to a flange and passes through the grid to improve things. Cooling the endcaps using water blocks is insufficient for one simple reason: stainless steel has terrible thermal conductivity. I'm planning to machine an aluminum chamber based on the new cube designs, and the larger ID will also help with stability at higher voltages.

Grid jig.
Grid jig.

I made a new lead box for the chamber which has helped cut down on x-rays a lot.

It has a lid.
It has a lid.

The data acquisition box was in dire need for an upgrade. Here's the much cleaner and less-prone-to-shorting V2, which has op-amps buffering the inputs/outputs to hide the impedances of the instruments, cables, etc... and a more spacious container. It'll also house the electronics, including full data logging, for a 2nd 3He neutron detector once that arrives. I plan to measure the anisotropy of the neutron output...

Control Box.jpg

More to come after I finish the 2nd neutron detector.
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Richard Hull
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Re: Fusor Update - Liam David

Post by Richard Hull »

Nice work, Liam! You have done amazing things in that little cross. I just gave up on my effort in so small a vessel. I look forward to your continuing reports.

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: Fusor Update - Liam David

Post by Mark Rowley »

Looking good Liam. Your lead box is similar to what I built which worked quite well. The remaining issue was leakage through the ceramic HV feedthru. Over 50kV the backscatter from that point was still an annoyance.

I’m sorry to hear about the Spellman demise and am going through a similar situation. I decided to try and wind my own flybacks and so far have had some encouraging results. I’m still waiting on some shipping delays with ordered parts but once done I’ll post more about the results and winding methods. Maybe something similar can be done with your supply.

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Re: Fusor Update - Liam David

Post by Andrew Seltzman »

I happen to remember that a few some forum members bought spellmans that didn't due to issues on the circuit board, those likely have salvageable flybacks in them or perhaps a good candidate for a circuit board swap.
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Re: Fusor Update - Liam David

Post by Liam David »

I bought another power supply which turned out to have the exact same issue. The left flyback is starting to get crispy. Will see if I want to do a flyback swap or return it.

On another note, my roughing pump is finally starting to give up the ghost after some 8 years. It's a 3cfm refrigeration pump that's survived one internal readjustment, but the motor is drawing too much current even though the vacuum is ok (~20mtorr on a good day). I scored a Varian SD-451, 14cfm monster off Craigslist for cheap. After an oil change, it pulls 8mtorr (edit: down to 5) on my chamber which has been sitting in atmosphere for a couple days. I'm sure it'll go lower after another oil flush and plasma baking. The highlights of this pump are an anti-suckback valve in case of a power failure (turbo pump saver) and quiet operation. The old pump sounds like a freight train in comparison.

I also bought 10lbs of paraffin and made a new neutron oven. Silver inbound along with titanium sheet for a cube fusor.


Old pump for scale
Old pump for scale

Neutron oven and indium bar
Neutron oven and indium bar
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Re: Fusor Update - Liam David

Post by Richard Hull »

Make sure you have your truss on when moving that new pump around. Sounds like the last mechanical pump you will ever need. Oh, be prepared for "oil mist aplenty". Those big boys can fog a room quickly, you gotta' cover that issue. As most everyone here knows I have vented mine since 2000 to the great out of doors. (bored a hole in the lab and sealed with silcone around the exiting pipe with a turn down fitting and a copper screen soldered over the exit. (keeps summer time outside insects out of the copper exhaust line.) I don't like bugs in my vacuum oil reservoir.

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Copper oil mist exhaust line installed for second time on fusor IV 2004.  First line installed on Fusor III in 2000.  Valve is critical to keep outside moisture out of the pump oil.  Kept off (blocked) when pump is not running.
Copper oil mist exhaust line installed for second time on fusor IV 2004. First line installed on Fusor III in 2000. Valve is critical to keep outside moisture out of the pump oil. Kept off (blocked) when pump is not running.
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: Fusor Update - Liam David

Post by Liam David »

Yep, ran the pump for a little while and the room started to smell like oil as expected. I had an activated charcoal filter for the old pump but need to make another, larger one. It's about 60lbs dry so quite the mass to move around.

Edit: Pump gets my chamber down to 2.8mtorr, low enough for my cold cathode gauge to come on automatically and I also can't ignite a plasma even at 30kV. The chamber has a tiny leak (~1torr overnight) so I think it can go lower.
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Re: Fusor Update - Liam David

Post by Liam David »

I activated some silver sheet today (2x6x0.010"). Max CPM on a 2" pancake ~3s after shutoff was 2500. Estimated "TIER" on the highest run was 7e5n/s, with arcing limiting operation to 30-35kV. Activation lasted between 3 and 10 minutes, with the longest run corresponding to the highest TIER. The neutron oven is composed of 4, 4x4x15cm paraffin blocks with the closest face about 8cm from the inside of the endcap. The silver is sandwiched between the two closest to the fusor.

Three separate runs
Three separate runs
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Re: Fusor Update - Liam David

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Doing what you just did is why I got into fusion. Neutrons!! Needless to say, fusion, for me, is a means to an end and that end is neutron activation. I am glad you are having fun with fusion like me. That is, doing something instructive and interesting with it. The beauty of fusion is only the neutrons get out of the reactor. The limited low energy x-rays are easily stopped, though pesky, to be sure. As we do more and more fusion, more activation possibilities come into view. Coupled with high stability longer run times due to water cooling, yet more possibilities are open to the careful and thoughtful amateur experimenter.

The fusor is a great auto-limited neutron source in amateur hands. It will never have flux levels or operational periods in anyone's hands that can create any dangerous or long lived isotopes. Just enough to enjoy advanced amateur science at a rarified level near the top of the heap. Cook 'em up in the morning and, yes, they are weak and need good instrumentation to enjoy the fruits of your labor and, blessedly, they are dead and decayed by bed time.

I have a nice demo for groups and even individuals who want to see the fusor. I have a soda and a sandwich on a saucer, which they see me munch on from time to time while demonstrating the fusor. I take normal silver and count it prior to activation allowing all to see it at background radiation level. Then, after running the fusor, they see the silver count over 2000 cpm on my 2" pancake, initially. They ask isn't that silver now dangerous? I now take a last planned bite to finish the sandwich and take the Fiestaware saucer the sandwich was on and place it under the pancake counter to roar at 30,000 cpm. They look aghast and shocked. I explain that the silver will be radioactive for only about one half hour and then be dead. The saucer I was eating off of will be radioactive for hundreds of millions of years and get even more radioactive than it is today over time. I then go to the white board and attempt to educate them in the most basic radiation science.

Liam, good 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: Fusor Update - Liam David

Post by Liam David »

I found what was limiting me to 35kV. The centering washer slipped and let the grid become misaligned. Moreover, I think I overtightened the grid stalk, which cracked the ceramic shielding washer when everything got hot. I just got some more washers in and will be back in business soon. The colorful sputtering probably didn't help the arcing either.

Offset cathode
Offset cathode

While everything was apart, I examined the cathode a little closer. There's a clear asymmetry caused by the stalk, certainly outside and probably inside the cylinder. The two bands on the ends thicken near the stalk and converge to it, and there's an interesting "cusp" on the inner wall. The patterns are more pronounced than last time because of the longer runtime and higher powers.


"Cusp" in pattern caused by stalk asymmetry...?
"Cusp" in pattern caused by stalk asymmetry...?

Ring where current flows in?
Ring where current flows in?

Asymmetric bands, caused by stalk.
Asymmetric bands, caused by stalk.


This is how the moderator is positioned for activation:

Moderator blocks
Moderator blocks

Silver from Rio Grande, with two pieces of indium.
Silver from Rio Grande, with two pieces of indium.
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Re: Fusor Update - Liam David

Post by Jim Kovalchick »

Liam,
Your grid pictures look like you are getting arcs secondary to the tube axis like I am. See my latest post for picture.

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Re: Fusor Update - Liam David

Post by Liam David »

I haven't had any arcing, just the occasional sparking thanks to my grid shifting off-center. The spots on the side are from secondary beams that form once the voltage gets high enough, something like 5kV.

Deliberately off-axis, secondary beam downward
Deliberately off-axis, secondary beam downward
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Re: Fusor Update - Liam David

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I love that "cock-eyed" view of the interior of the cathode. Lots of interesting data in that view related to fields.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
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Re: Fusor Update - Liam David

Post by Jim Kovalchick »

Liam,
I meant to say beams not arcs. I can see them in your latest picture.

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Re: Fusor Update - Liam David

Post by Liam David »

Arrived today, will be machined likely next week:


PXL_20210224_221335526.jpg


Both the chamber and endcaps will be fully water-cooled, and I have a few modifications that should help the field symmetry. I'm looking to push past 60kV, and with how I've arranged the water cooling, the angular neutron distribution should be minimally affected. Simulations show a max temperature of ~30C at the beam spots with 1500W input power, which is far above the 600W my supply can do at 70kV.


Getting better symmetry, and can push 45kV with the repaired feedthrough. There's static buildup somewhere and some sparking that's limiting the voltage.


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Re: Fusor Update - Liam David

Post by Mark Rowley »

I always enjoy reading your updates Liam. Top notch work.

Very much looking forward to your cube build. I foresee good things on the horizon!

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Re: Fusor Update - Liam David

Post by Liam David »

Thanks, everyone, for the compliments. Been spending as much time on fusion as I do on school recently...

I found the actual source of the arcing and instabilities, which was only exacerbated by the offset grid. In moving the feedthrough quartz up and down, both for positioning in the chamber and servicing, vacuum grease from the o-ring and dust built up in a small ring. This got baked onto the quartz and limited the voltage to ~35kV. Now with some conditioning I can hit 50kV, limited primarily by x-rays. I have the lead shield top off for air cooling and scattering is an issue. Neutron rates are ~800kn/s @ 45kV, 8.56mA and can be held indefinitely, with brief excursions >1.3e6 (~100kcpm on the tube). Heating prevents me from exceeding the mega mark continuously.
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Re: Fusor Update - Liam David

Post by Richard Hull »

Good work Liam! 1.4 million n/s is about the best I ever did with fusor IV at 45kv. (my current limit on voltage.)

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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: Fusor Update - Liam David

Post by Liam David »

Maximum neutron rate is now 2e6 at 50kV, 8.56mA, though excessive sparking prevented me from maintaining the output. When I lower the current, however, I can push the voltage much higher. At 59kV, 0.86mA, it produced 4.1e5n/s, which gives a Q value of 9.2e-9. The theoretical output at 59kV, 8.56mA is 4.1e6n/s, which is a factor of 2 higher than I measured at 50kV, 8.56mA. Seems to check out. There were brief forays into Q>1e-8, but this could just be due to Poisson statistics with the counts. The field at the feedthrough is starting to get pretty high--high enough that it likes to charge up ungrounded metal bits in the vicinity. I will need to add some field control to the top, probably a small toroid.

Plasma.jpg
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Re: Fusor Update - Liam David

Post by Liam David »

A quick update while I'm working on upgrading my new system, which will hopefully come online in the next month or so.

I have a bubble detector and can thus finally calibrate my detection gear, but I've found a discrepancy in the results.

Over 988 seconds at ~33kV, 8.5mA:
3He detector at 48cm registered 156546 counts
Bubble detector (24/mrem) at 22.5cm gave 70 bubbles
Ludlum 2363 with Priscilla probe at 39cm (to the face) accumulated 0.44mrem

OpenMC simulations and 3He tube give 1.09e6 TIER
The bubble detector gives 5.27e5 TIER
The Ludlum 2363 gives 2.40e5 TIER

I'm not surprised that the simulations are off by a factor of ~2 as they cannot account for everything and material composition/distribution assumptions create errors. I'll look into why but it's certainly good that it's the right order of magnitude. What surprises me the most is the bubble detector/Ludlum discrepancy... It's possible that the Ludlum calibration has drifted since 2013, but a factor of ~2 seems unreasonable. Finn noted in a recent post that the same detector indicated a dose rate lower than expected based on the voltage/current input. Perhaps it has the same cause? My first guess, assuming I'm not missing something obvious, is that the detector distances are not in the far field relative to the source distribution. Unfortunately, my lab space and relatively low output make far-field measurements practically impossible. Also, it's certainly not thermal scattering as the Ludlum reads lower and it's sensitive from thermal to many MeV.
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Re: Fusor Update - Liam David

Post by Matt_Gibson »

Nice to see some more results with the Ludlum and Prescila probe.

I’m trying to judge how good/bad my recent success is…I hit just over 8mR/hr with mine running 39kV and 7.5mA, 2.5cm from the face of the chamber.

Can you get your “hammer” within 2.5cm of your fusor to see what you get?
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Re: Fusor Update - Liam David

Post by Liam David »

What's your total distance from the chamber center to the probe face? With your chamber size you have all the info you need to approximate TIER.
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Re: Fusor Update - Liam David

Post by Richard Hull »

Neither Matt nor Liam in the above posts gave a critical value!!! How much fuel did you have? Let's get it into our heads. Three that is (3) values are important

1. Voltage: Where on the cross sectional chart of the fusion "fuel" are you operating?
2. Current: How many possible fusion "fuel" deuterons are you putting into the ongoing reaction?
3. Pressure: How much actual Fusionable "fuel" do you have in the reactor vessel?

I operated at 5 microns and 30kv! Tells us nothing
I operated at 30kv and 5ma! Tells us nothing
I operated at 10 microns and ran at 20ma! Tells us nothing

Give three full operational parameters. Then we will know the full story about where you were operating. It is certainly assumed both Matt and Liam knew their running pressures. Sadly, we do not.

I really hate to keep reiterating this. I would love to attempt to weight in on the conundrums above, but have no idea where you guys were so far as operational points.

Even with different reactor geometries and sizes and now three methods of measuring, It would be nice to know one full indisputable operating point before attempting to help in comparing apples and oranges.
With all these variables in the mix, it would be nice to have one given constant starting point.
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: Fusor Update - Liam David

Post by Matt_Gibson »

I’m running at 18.1 microns with a deuterium flow rate of 1.5sccm. Hammer face is about 3in from center of chamber.
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