Fusor 2020

For posts specifically relating to fusor design, construction, and operation.
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Mark Rowley
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Fusor 2020

Post by Mark Rowley »

About a month ago I decided to try something similar to the cube Fusor Jon Rosenthiel and Joe Gayo built. The main differences being that I decided to machine mine out of 3.75” 6061 round and (for now) I’ll be using a standard grid.

All in all it was fairly easy and cost less than $120 in parts. It’s important to note that the viewport was already on hand but building one that was just as effective would’ve only cost me an afternoon in the shop. A thick fused quartz window can be found on the auction sites for $10-20 if one is patient. Making the flange from 2” dia 6061 would be less than $5.

The entire chamber uses Viton o-rings and pulled a sub 1 mTorr vacuum on the first test. The key was to ensure the o-ring grooves are polished to a mirror finish. Simple task with a Dremel tool and some polishing compound.

Except for the flanges, I made the KF25 fittings from scratch. They too use Viton o-rings.

Here’s a quick one minute video showing it’s construction from beginning to Star Mode.

https://youtu.be/obhkgGy9c6g

After feeding it with deuterium today I made a few neutrons (2 bubs) but was quickly alerted to xray problems over 20kV. I never went past 25kV with the makeshift lead shielding I had in place as even backscatter was a concern. So as of now I’m building a total lead enclosure for the Fusor. Not a difficult problem as it’s a simple cylinder and there’s plenty of lead on hand to accommodate. Once done I can begin ramping up the voltage and comparing performance with the old cross Fusor.

Mark Rowley
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Mark Rowley
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Re: Fusor 2020

Post by Mark Rowley »

Here’s a pic of the whole chamber broken down into its basic components. Excuse the greasy mess...it came off the machines a few hours earlier.

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Mark Rowley
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Re: Fusor 2020

Post by Mark Rowley »

Here’s a chamber diameter comparison with the earlier 2.75” system.

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Richard Hull
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Re: Fusor 2020

Post by Richard Hull »

Wow, wow and wow! That chamber could be a super heated steam vessel! No thin walls need apply! I see you have one of those great antenna bulkhead insulators like I obtained and sold back in the 90's and early 2000's. You did a great job of adapting. This was a joy for the eyes to see. Fabulous execution. Any time you can zero a TC gauge in a chamber is a big win. Great shot with deuterium with fabulous star. You know that window will go to crap soon as deposition takes place, I am glad you drew first blood with the pix while it is fresh.

I can't say enough about this posting for it is an inspiration to those wanting to see how it is done and done right. I am breathless, but not quite speechless as this deserves applause.

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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Mark Rowley
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Re: Fusor 2020

Post by Mark Rowley »

Thanks Richard. Tbh, I’m not sure what’s more enjoyable.. construction or operation!

Today was the true maiden voyage for this Fusor. After cluttering the Fusor cart with sufficient lead shielding I was able to conduct a fairly decent first test.

First off, I have to say this chamber has greatly improved voltage control compared to the small 2.75” Fusor. Although not extremely problematic, the 2.75” system would periodically suffer unexpected power fluctuations resulting from plasma issues in the chamber. The new system has very smooth and steady voltage control making operation a pleasant experience. I also noticed an improvement controlling deuterium flow. No longer does a slight touch of the needle valve result in an abrupt pressure increase. It’s now a very gradual and controllable response.

Neutron detection (CHM11 / Ludlum 2221) uses the same amount of moderator and distancing as with the previous system. My BTI bubble detectors still seem to be operational so the better of the two was used in this run.

I’m still learning how to drive this new Fusor and what gas pressures and flow rates work best. The best run for today was 20 bubs in 3 minutes at ~17cm distance. Average cpm with the CHM11 was ~6500 which coincides with the BTI results. I’m fairly confident this system is capable of much higher output once I find the optimal conditions AND employ the deuterium cold trap.

One thing I noticed that’s somewhat concerning is this aluminum chamber heats up pretty good. Jon mentioned something similar with his cube Fusor. Quite possibly I’ll have to resort to some type of active cooling system similar to Carl Willis’s Fusor with the copper tubing. Time will tell...as of now it’s being cooled with forced air.

Mark Rowley


The now cluttered looking Fusor cart.
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Dennis P Brown
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Re: Fusor 2020

Post by Dennis P Brown »

That is impressive machine work and fusor! Boring out that aluminum cylinder must have been really time comsuming. Your final product is a very clean and very practical design.

Congrats on getting your new fuusor running and with such excellent neutron production.

I had a large steel chamber fusor and it did need water cooling.

By the way, what is your voltage and current?
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Mark Rowley
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Re: Fusor 2020

Post by Mark Rowley »

Thanks Dennis
Boring the cavity was probably less than an hour...or equivalent to my weekly ritual of mowing and trimming my front lawn. So it wasn’t bad at all. Polishing the inner walls took about the same time. The annoying part about all that was the mess! Chips and bits everywhere not to mention the splatter from using the high speed cylinder bore polishing tool... ugh. But all for a good cause!

Roughy 40kV / 3mA / 45mTorr D2 for the 3 minute BTI results.
This first run barely lasted 20 minutes. Trying to learn the new parameters used my 100mL D2 reservoir fairly quick so by no means do these numbers reflect efficiency or anything close to optimal calibration. I’ll be giving it another go in the next several days.

Mark Rowley
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Richard Hull
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Re: Fusor 2020

Post by Richard Hull »

Great run Mark! You are cookin' with gas, as the old expression goes. Really good report, what was the voltage, average current and average pressure on the run? All of this is a must when speaking of a run regardless if it is just a test run or a run for a seriously stable system output test.

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 2020

Post by Mark Rowley »

The bulk of the 20 minute run was adjusting flow rates and determining where extinguishment took place. When I got to about 6500cpm with the Boron tube I only had about 30% of my gas left. At 6500cpm, input power was about 40kV at 3mA. D2 flow was at 45mTorr. While purring away at roughly 6500cpm with that input power, I left the BTI there for 3 minutes which resulted in 20 bubs.

I’m currently trying to remedy a slight leak from the cheapo KF25 gate valve I’m using. Nothing bad, just annoying. Probably the only fix is to purchase something decent.

Mark Rowley
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Re: Fusor 2020

Post by Richard Hull »

I realize that, early on, pressures, voltages and currents can vary during a run. The human brain can make a fair guess at the general averages of the variables. Even a best guess is better than a poke in the eye with a sharp stick. It gives us a feel for what went on. The bubbles tell the story. Fix your system and the boron detection system with moderator before your BTI's go bad and run a lot of runs once fixed and you can eliminate the need for the bubble detectors in future once you get a multiplication factor on the counts from you neutron detection system to isotropic emission.

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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Mark Rowley
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Re: Fusor 2020

Post by Mark Rowley »

That’s definitely the plan however I think I’m destined to one last BTI purchase for the linear pinch project. Once I get this new Fusor stabilized I’ll be resuming the Columbus-1 project. I needed a change of pace before going full bore into the pre-ionization phase of the pinch tube. I’m hopeful to get enough pinch neutrons so I can go the activation route and abandon the BTI’s altogether. As we all know, BTI’s are an apoplexy inducing money pit.

But back to the Fusor2020, it’s current neutron output is more than enough for indium activation. After a few indium activations I’ll be proceeding to silver. Tim Koeth helped out with some premium silver foil so I’ll be transitioning to that fairly soon.

Mark Rowley.
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Re: Fusor 2020

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Today’s run lasted a total of 10 minutes. Within that time span, I continued to make adjustments and on several occasions turned off the power supply so I could safely adjust the diff pump gate valve.

The top BTI dosimeter reflects the total 10 minute run at 45 bubbles.

The bottom dosimeter reflects a 3 minute timed count when I got the cpm to somewhat stabilize around 6kcpm (45mTorr D2 / 45kV / 3mA). During the count, the Fusor fluctuated twice and each time dropped to about 5500cpm. Total of 19 bubbles. Both dosimeters were at approx 17cm from the central grid.

Unfortunately, this is the second of only 2 runs where I’m once again going to have partially open the chamber, thus ruining any conditioning it had. Looks like I may have overtightened the viewport causing some damage to the Viton o-ring. Not a big deal, but slightly annoying.

Mark Rowley
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Re: Fusor 2020

Post by Tony Lai »

Wow.... Would you mind me ask what is the inner diameter of your chamber? Planning to make one with smaller size just like Jon's cube, but just wondering if chamber size affacts fission efficiency.
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Re: Fusor 2020

Post by Mark Rowley »

2.3” inner diameter.

I’m not sure what Jon’s cube is bored out at.

Fwiw, this 2.3” size is a phenomenally better system in all regards than the smaller cross fusor. Very stable operation which allows the operator to establish a desired neutron flux rate and walk away while it activates target material. The cross required constant fiddling with the voltage and deuterium flow rate to keep the numbers up.

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Re: Fusor 2020

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Cooling has become a pivotal issue. I’ve tried various methods of forced air including refrigerated forced air. All have worked to some degree with the refrigerated arrangement being the best. Unfortunately the latter system only works a few minutes longer than regular forced air which results in a fail for long term activation experiments.

Recently Jon Rosenthiel shared a spectacular approach to water cooling with his cube fusor. On one side of the cube, he milled in a water maze where he pumps coolant through during high output runs. After a 900 watt 20 minute run, the cube hit a peak of only 41 degrees C (105F)!

Here’s Jon’s very detailed post:
viewtopic.php?t=13579

Such a result is presently beyond compare and also extremely clean. No soldered on copper tubing which only has very limited surface contact for thermal exchange.

As of now, I’m about 50% complete with a similar modification to Fusor2020. I will be incorporating two watermaze arrangements (one on each side).

The mazes are complete. All that needs to be done now are the 3/8” caps and related aluminum NPT fittings.

Mark Rowley

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Richard Hull
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Re: Fusor 2020

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I have actually mused over a totally submerged fusor with a cold water tank circulating system. 100% coolant contact. It is definitely doable although a bit bulky and heavy for all but the smallest systems. Gotta' keep musing and thinking. A spherical system would look like a sea mine with only the hv insulator and vew port poking out of the water. A nice cylinder fusor would have only the HV terminal out of water. The view port would be viewable under water via a clear tank or a separate nearby view port in an opaque metal or plastic tank. Such a system would require a larger view port of perhaps 3 or more inches. Great effort Mark!

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 2020

Post by Dennis P Brown »

While I used flexible copper tubing to wrap my fusor body (and conductive epoxy to hold it in critical places) and ran water, one isn't required to use water. Standard available propane could be used - it has an even greater heat capacity then water(!) and better still, it is non-conductive. Yes, leaks create an explosive hazard and only someone really capable of creating leak proof plumbing should consider such a system. But it is used in many modern cooling devices (std. AC units), is cheap, non-toxic, and using an old refrig. compressor can be easily assembled (I did this in college to achieve minus -40 C for a diffusion pump cold trap.)
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Re: Fusor 2020

Post by Jon Rosenstiel »

Looks really good Mark, I’m impressed.

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Re: Fusor 2020

Post by Mark Rowley »

Cooling maze modification completed. Today’s test made sure there were no leaks by pumping chilled coolant through the system for a couple hours.

The cooling lines coming from the rear maze will require a slight modification to the HDPE moderator and X-ray shield. With any luck I should be able to initiate a fusion run in the next day or two.

Mark Rowley

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Richard Hull
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Re: Fusor 2020

Post by Richard Hull »

Fabulous effort and no leaks...Great! Ain't it a bear how one, when upgrading, has to change other stuff that was fine until the "new thing" forced alteration of, or cutting, or boring some wonderful thing that was crafted earlier. Add-on stuff always seems to get in the way of what was "finished goods". In the end, during research and improvement, nothing is finished goods. Very little is ever finalized. We keep on searching for improvements in all areas.

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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Mark Rowley
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Re: Fusor 2020

Post by Mark Rowley »

First run with the cooling maze was a resounding success. Following a 15 minute sustained run at a roughly estimated neutron TIER of 1.3E+6 it never peaked over 87F (30.5C). Cooling fluid was water with Rislone Hy-per Cool Super Coolant. As of now, the coolant is only recirculating within a 2 gallon reservoir with no radiators or extra cooling system. Adding a couple fan cooled computer-type radiators (as in Jon’s system) is something I’ll probably employ in the future.

In addition to these changes I opted to replace the Yellowjacket HVAC pump with a much quieter and more efficient Welch DuoSeal 1402. Being a higher capacity pump, it’ll rough down to almost 9mTorr in a couple minutes. The Yellowjacket could rough the system down to around 12-13 after about 5-10 minutes. Performance wise with the fusor it’s negligible but at least the lab is a once again a quiet place during operation.

One other bit of good news is the fact that I was able to keep the HDPE moderator in the exact configuration and distance as it was when BTI calibrated a month or so back. I’ll double check calibration in the next few days to see if the water in the two mazes have made any significant differences with moderation.

Mark Rowley

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Richard Hull
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Re: Fusor 2020

Post by Richard Hull »

Great report and I am glad you are running cool. I used a yellow Jacket from 1997-2003. It could hit 8 micros on fusor II , but with the increased volume in fusor III, it hit 10 or12 microns in a few minutes. Ultimately, like you, I swore off direct drives and went for the much more soothing lup-lup lup of a belt drive, slow winder. Great work.

The key is that, once calibrated, never move the moderator or significantly alter the positions of any major physical object around or near the moderator. Fusor IV was frozen in space 2004-2019. Right now, as I am un-calibrated I have complete freedom to just mess the entire system up and introduce or remove anything as it pleases me. I really do like this, as I can experiment and allow the 3He tell me whether I have made a quantitative improvement. With the silver activator buried in the moderator, I can always prove I am doing fusion over and above any questions regarding the 3He counter which we all know is showing fusion is taking place. Still.......Dead silver made radioactive in a few minutes always shuts up any doubters related to electronic neutron counting instrumentation. (Not that anyone has doubted the 3He heralding fusion.)

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 2020

Post by Mark Rowley »

A very good point Richard. Totally plays into why I’m having so much fun with activation lately.

After a second test run this afternoon I noticed an annoying backscatter problem. Easily fixable but moderator configuration will undoubtedly get altered. If the aging BTI’s fail beforehand, I’ll be just as happy with activation numbers and gamma spec.

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Re: Fusor 2020

Post by Mark Rowley »

Before resuming the BoT2021 project, I’ve decided to try something unique with this fusor.

Reviewing old disassembly photos from last year, I came across the beam impact “lozenge” images from the inside wall.

C35FB9A7-E9FD-47D9-9312-962B930B88EF.jpeg

The lozenges expectedly line up with each of the 6 “star mode” beam radials from the grid.

Since I’m making some deuterated titanium targets for the BoT2021 project, I figure I’ll try installing several in the fusor before it’s temporarily disassembled. Placement will be on the chamber wall in the same location as the lozenge impact marks where they will serve as deuterated targets.

If the ion beams have any type of BoT characteristics as indicated by fusors with cylindrical grids, this might result with a substantial increase in neutron production… or it just may fail miserably.

Either way, I’ll update with the results soon. And of course this is all incumbent on the success of the deuterizing apparatus.

viewtopic.php?t=14055

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Re: Fusor 2020

Post by Jim Kovalchick »

Mark,
I recommend using small Ti targets. I used large pieces of it in mine and found pressure control became difficult. I was also using a ring grid then, so perhaps your multi beam arrangement may help avoid big temperature induced pressure changes.

Jim K
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