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 » Mon Sep 28, 2020 4:26 am

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Liam David
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Re: Fusor Update - Liam David

Post by Liam David » Wed Feb 03, 2021 9:15 pm

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
Plasma and Whiskers.jpg
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.jpg
Grid jig.

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

Lead Box.jpg
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 » Wed Feb 03, 2021 10:00 pm

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Mark Rowley
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Re: Fusor Update - Liam David

Post by Mark Rowley » Thu Feb 04, 2021 12:10 am

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.

Mark Rowley

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Re: Fusor Update - Liam David

Post by Andrew Seltzman » Thu Feb 04, 2021 3:01 am

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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Liam David
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Re: Fusor Update - Liam David

Post by Liam David » Wed Feb 17, 2021 11:26 pm

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.


Size Comparison.jpg
Old pump for scale

Paraffin Activation Oven.jpg
Neutron oven and indium bar

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Richard Hull
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Re: Fusor Update - Liam David

Post by Richard Hull » Thu Feb 18, 2021 6:02 am

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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IV const 04 (3) Anno.jpg
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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Liam David
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Re: Fusor Update - Liam David

Post by Liam David » Thu Feb 18, 2021 3:29 pm

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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Liam David
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Re: Fusor Update - Liam David

Post by Liam David » Fri Feb 19, 2021 11:26 pm

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.

silver activation.png
Three separate runs

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Re: Fusor Update - Liam David

Post by Richard Hull » Sat Feb 20, 2021 5:39 am

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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