Nick Babusis Fusor Progress

[Nick Babusis]

Project Objectives
The goal of this project is threefold:
1. Design and build a simple fusor for <$5000 that can be easily modified or replicated.
1a. Design the fusor to be made primarily from COTS components and publish detailed design information to facilitate replication. Hopefully, this design can serve as a starting point for inexperienced fusioneers.
2. The fusor must produce (and detect) >500k neutrons/sec isotropic.
3. The fusor must be useful as a high vacuum chamber and high voltage power supply for other projects.

Progress as of π/2023
I have completed the vacuum system except for the main chamber and electrical feedthrough. Both my TC and capacitance manometer gauge have calibration issues and do not display the actual pressure (TC gauge has an offset that cannot be compensated, Baratron reads pressure ~1.28x higher than actual.) Both gauges have been calibrated against known good gauges and show that the system reaches 4 micron with the roughing pump (which blanks off at 1.5 micron) and <1 micron with the diffusion pump on, even though the needle valves seem to be leaking slightly. The Ludlum model 2000 scaler works with a gamma scintillator probe, and the high voltage probe has been built and calibrated at 600v.

ToDo
I still need to:
1. find an XRT and build the power supply.
2. build the main chamber hemispheres. (I’m sending those out to be welded professionally, which is taking a long time)
3. Verify my neutron detection scheme will work and calibrate the detector. Ludlum does not want to calibrate my home-built, soviet tube detector for me, so I may have to find another way.
4. Verify my feedthrough design with FEMM
5. Obtain D2O (most companies will not sell to an individual)
6. Figure out how to calibrate my thermocouple gauge for deuterium. I though I just had to multiply the reading by the conductivity of D2 relative to air, but that doesn’t agree with the data for the micropirani gauges here: https://www.pfeiffer-vacuum.com/en/know ... asurement/


Once everything is tested and the fusor is producing neutrons, I will be posting a google drive link with all my bill of materials, design drawings, calculations, datasheets, and operating procedures

Current fusor setup. The gauge calibration has since been improved slightly. Note that the TC gauge is offset by 10 micron.

Updated plans for the fusor.


Mistakes and Lessons Learned
I burnt out the Baratron gauge by turning it on in 1 atm (turns out the maximum storage pressure was 1.25 atm, the maximum operating pressure was 1 Torr). Surprisingly the gauge still kinda works after removing the burnt component, although the slope is off by 1.28x and it drifts by ~.5 micron for no apparent reason. I am debating about replacing it. I also made the mistake of cleaning the plastic sight glass on the roughing pump with IPA, causing it to crack immediately. Another mistake I made was using using too low resistance potentiometers on the high voltage probe, making it have a very narrow calibration range when using a 1M ohm meter. All the other mistakes I've made I still have yet to discover!

[William Turner]

Triple Points

Shielded

Use a finite element electrostatic field solver to test your ideas (like FEMM).

Regards,
Will

[JoeBallantyne]

Why are you building a relatively large chamber, that requires you to pay for custom welding work, when you can just use standard COTS vacuum parts (like either KF or conflat 4 or 6 way crosses or 3 way tees) to build your fusor?

AFAIK, currently, the best performing fusors are all small. (Like inner diameters of 3 inches or less, and maximum "beam" lengths of 5 inches or less.)

They are also all made out of aluminum.

Joe Gayo's cube fusors are aluminum and small.

Jon Rosenstien's cube fusor, is also made out of aluminum and is small.

I believe that those are currently the highest neutron output fusors of anyone here at fusor.net.

Joe.

[Richard Hull]

I think Nick is shooting for the classic design look. Small fusors, especially cubes, that produce like Jon operates, require far more skill and materials to operate over a larger, more forgiving, classic system. I believe the goal sought is for a first ever posting of a bill of materials and costs, as noted, for a beginner's successful fusor that is simple to operate.

We have had a lot of requests over the last 23 years for a (kit of parts and costs that is rather complete for an amateur fusor by beginners).

I have always thought this was a worthless effort for those arriving here as the final price is never fixed, nor are the components, based on lucky purchases, inventive kludges and the electronics and instrumentation variability.

However, if Nick succeeds in supplying a comprehensive list of parts with a bill of materials and his effort does reach 500k n/s ISO, and is in the $4000-$5000 range, it will be a landmark effort.

It will do two things. Scare off low budget future applicants, or act as a challenge to those who feel that, through skill and verve, seek to beat the price tag. This latter effort is what 90% of the successful folks have dealt with since 1999 and why I feel a list of components with a bill of materials is somewhat of a lost cause and would only stop the weak, fiscally poor, non-hackers, who arrive with zero skill sets, thinking they can do fusion.

All of the foregoing flies in the face of the absolute fact that fusion is easy to do! This beggars the definition of "easy to do". At what level of expenditure, knowledge base, skill set and verve is the definition of "easy to do" met and satisfied, at the amateur level?

At any definition, scientifically, true fusion is easy to do as a physical process.

Richard Hull

[Matt_Gibson]

Unless you already have a lead on getting an x ray transformer or similar, you might want to focus efforts on the power supply. A good power supply is very difficult unless you have a few grand (eBay has a few suitable ones for $2-3k).

-Matt

[Nick Babusis]

Why are you building a relatively large chamber, that requires you to pay for custom welding work, when you can just use standard COTS vacuum parts (like either KF or conflat 4 or 6 way crosses or 3 way tees) to build your fusor?

AFAIK, currently, the best performing fusors are all small. (Like inner diameters of 3 inches or less, and maximum "beam" lengths of 5 inches or less.)

They are also all made out of aluminum.

Joe Gayo's cube fusors are aluminum and small.

Jon Rosenstien's cube fusor, is also made out of aluminum and is small.

I believe that those are currently the highest neutron output fusors of anyone here at fusor.net.

Joe.

Hi Joe,
I went with a large spherical chamber so that I can run a greater variety of non-fusion experiments in the same system than I could with a COTS cross or tee. Making it out of stainless steel allows for easier welding and modification. The welding required is certainly a drawback however.

As Richard said, this will serve more as a starting point for new experimenters than a fusor kit. My goal is to provide a known working setup for a reasonable price for those who don't want to do a deep dive on the design of every aspect of a fusor. Certainly it cannot be built naively, but it should cut down on the mistakes and development time of people who are more interested in the use of their fusor than its design.

As for Will's comments, I will likely have to get rid of the triple junction in the feedthrough, but your "shield" looks quite difficult to make and I am still concerned about the field strength on the surface of the .094" diameter feedthrough conductor. I will run some FEMM simulations, starting with just shortening the steel tube in my design.

[Richard Hull]

Nick please do not use block quotes We hate these even though they are common on many sites where weak minded people reside. We are smart cookies and have read all preceding posts! No need to clog up a reply reposting something immediately above in some futile attempt to force folks to re-read old text in the thread.

Your third paragraph above is correct. You should have begun your reply with..."as regards Joes comments above..." Just avoid block Quotes.

Richard Hull

[Rich Gorski]

Hi Nick,

You can purchase heavy water (D2O) at a number of companies. Its not a regulated commodity. I recently purchased 10 gms at United Nuclear for $50. All you need is a credit card to purchase online. 100gms for $295.

www.unitednuclear.com

Good luck with your build.

Rich G.

[Richard Hull]

Sadly, it was $1.00/gram for a long time and of late, it has been going out of sight! I bought some long ago for $89 for 100grams. I bought a couple of years back for $100 plus $10 shipping for 100 grams. Inflation really hit the heavy water market.

Richard Hull

[Nick Babusis]

After many FEMM simulations, it looks like my best bet is to not modify the feedthrough conductor diameter, since any tube (metal or dielectric) that I could slide over the conductor would increase the surface field strength. Instead I will leave the conductor unmodified and limit the voltage to 50kV to keep the field universally <1.5E7 V/m. For connecting the grid, I will be trying a BeCu screw terminal. These have a lower melting temperature than the stainless steel terminals I was originally going to use, but they act as great heat sinks to locally cool the grid wires, and I have used them before to mount white-hot tungsten filaments on a hall effect thruster.

FEMM simulation at 50kV with a plot of surface field along the vacuum section of the feedthrough conductor:

Feedthrough with BeCu grid connector:

[William Turner]

If you post your *.fee file, I'll show you one option...

Will

[Nick Babusis]

Here is the .fee file. I had to change the extensions to be able to upload it, but it should work if you change it back to .fee. Note that I used the 0V boundary condition on some parts of the ceramic touching the flange on the vacuum side since these areas are grounded via a thin metal coating.