Nick Babusis Fusor Progress

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Nick Babusis
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Nick Babusis Fusor Progress

Post by 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
IMG-5356.jpg
IMG-5355.jpg
IMG-5352.jpg
Current fusor setup. The gauge calibration has since been improved slightly. Note that the TC gauge is offset by 10 micron.
Fusor Diagram v5.png
Electrical Feedthrough v2.png
High Voltage Diagram (1).png
HV probe diagram (1).png
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
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Re: Nick Babusis Fusor Progress

Post by William Turner »

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

Regards,
Will
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Re: Nick Babusis Fusor Progress

Post by 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.
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Richard Hull
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Re: Nick Babusis Fusor Progress

Post by 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
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
Matt_Gibson
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Re: Nick Babusis Fusor Progress

Post by 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
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Nick Babusis
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Re: Nick Babusis Fusor Progress

Post by Nick Babusis »

JoeBallantyne wrote: Wed Mar 15, 2023 10:32 am 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.
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Richard Hull
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Re: Nick Babusis Fusor Progress

Post by 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
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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Rich Gorski
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Re: Nick Babusis Fusor Progress

Post by 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.
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Richard Hull
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Re: Nick Babusis Fusor Progress

Post by 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
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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Nick Babusis
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Re: Nick Babusis Fusor Progress

Post by 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:
Screenshot 2023-03-17 015716.png
Screenshot 2023-03-17 015737.png
Feedthrough with BeCu grid connector:
unnamed.jpeg
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Re: Nick Babusis Fusor Progress

Post by William Turner »

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

Will
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Re: Nick Babusis Fusor Progress

Post by 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.
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Re: Nick Babusis Fusor Progress

Post by Nick Babusis »

Progress as of 4/18/2023
The vacuum system is (mostly) finished. Surprisingly, I found that while leak checking a 1 micron/second leak around the needle valves by dousing joints with isopropanol, I reduced the leak to ~0.01 micron/second. Maybe these valves will work after all. The baratron gauge that started smoking when exposed to atmosphere has been recalibrated to the best of my ability, but has a ~2x slope offset at pressures <50 micron, and the zero drifts by ~1 micron. I do not really have the budget to replace it though.
Fusor_prelim_setup.jpg

I am now using a 150kVp, 150mA iron core x-ray transformer as my power supply from a Gendex Uni-Matic 325. I added a 50k ohm ballast resistor under the oil and used 40kV wire inside vinyl tubing for the high voltage cable. I managed to modify the transformer by adding an additional output such that it can still function as an x-ray machine if desired.
Gendex_XRT.jpg
Drill_x_ray.JPG

I am using a SNM-11 corona tube neutron detector connected (via 100M resistor) to a Ludlum model 2000 scaler. Unfortunately, I cannot detect gamma rays from a Co-60 check source at any discrimination or any voltage within the tube's operating range. The scaler detects gamma rays fine with a scintillation detector, so I expect the tube will have to be replaced (unless I did something dumb in my setup). This is the housing I built for it:
SNM11_housing.jpg

I performed a preliminary test with a maximum 50kV CO2 laser power supply. The plasma ignited, but had interesting starting behaviour where it generated a star pattern for ~0.5 seconds before transitioning to a diffuse glow as I slowly raised the voltage. The white color is due to the camera's color correction.
initial_plasma.png
diffuse_plasma.png

Lessons learned
  • D2O can be purchased cheaper than expected (provided you have a commercial shipping address) from Spectrum Chemical ($205/100g) or Fisher Scientific ($214/100g)
  • If using outlet power strips, check their maximum current draw. One of mine switched off while running the roughing pump, causing atmospheric pressure to enter the hot diffusion pump for a few seconds. Surprisingly, the pump oil appears to be undamaged.
    Do not use a webcam with built-in color adjustment to monitor the plasma.
ToDo
  • Fix the detector tube and calibrate the neutron detection system. I still have not found a viable method of calibrating such that I can be certain I can detect neutrons and only neutrons on my budget. Ludlum is not willing to calibrate my detector using the ancient soviet SNM-11 datasheet I found online.
  • Add a variable primary transformer to the XRT power supply.
  • Test the PEM fuel cell D2O separation system.
  • Determine if I will need a new needle valve. The current valves seal poorly, and I suspect they may be leaking significant quantities of air through the handle.
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Re: Nick Babusis Fusor Progress

Post by Dennis P Brown »

I see a major and deadly issue with your setup- where is your massive shielding system? That 150 kV power supply (at 150 ma!) will create a lethal X-ray radiation hazard if you raise anywhere in that range. You'll need a wall shield. Even 50 kV is very dangerous and will produce a large x-ray flux. So, again, you need proper shielding.

From the look of your setup it appears that in order to operate the various devices you are exposed to the chamber. I wouldn't run that thin-walled chamber above 30 kV without proper shielding. In any case, a proper x-ray radiation detector to measure the shield system for leakage is required. And the back wall, is there an adjoining room? If so, is that area closed off when operating? Remember, one must protect other people from radiation as well.

As you know, that high voltage cable is useless much above the 40 kV so be extremely careful or never operate the supply above its rated level.
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Rich Gorski
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Re: Nick Babusis Fusor Progress

Post by Rich Gorski »

Nick,

I want to echo the danger comment by Dennis. The X-ray transformer power supply (150kV, 150mA) is dangerous both from an X-ray point of view as well as a high voltage/high current injury point of view. It is deadly! If you get your fusor to operate at 50 kV even 1 mA it will produce a huge X-ray flux. When you are ready to operate above 30 kV you need to seriously think about adding lead X-ray shielding. The thin stainless steel wall of the chamber won't be enough. Even adjacent rooms could have a significant X-ray flux. When I run my device above 30kV (situated in the basement) I can detect X-rays on the floor above. That being said, it looks like it won't be long till your producing neutrons!

Rich G.
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Re: Nick Babusis Fusor Progress

Post by Rich Gorski »

One additional story. During my graduate studies at school, myself and a few other students built a 125kV ion accelerator. It also used a similar deadly X-ray transformer. Although that was a long time ago I remember running the accelerator at around 100kV with a low maybe 0.1mA ion beam into a metal target. The X-ray flux was so intense and high energy that we could detect X-rays bouncing off a mirror we had set up to watch the device around a corner of the room. That was a good 30 feet distance... and along the beam line X-rays were penetrating through the wall, into the hallway, through another wall and still detectable in a classroom. So, although it's unlikely you will get to 100kV with your fusor (not impossible), be careful !

Rich G.
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Re: Nick Babusis Fusor Progress

Post by Richard Hull »

That is an industrial level x-ray power supply! I am sure any effort to calm it down to fusor level beyond 50kv will result in arcs and burn throughs....

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: Nick Babusis Fusor Progress

Post by JoeBallantyne »

Given that you have the complete x-ray system, many times the controls allow you to set the voltage and current put out by the supply.

If you have full control of the voltage using the built in controls, I would suggest just using those.

As long as you are confident they work properly, and they give you the ability to set the voltage down to 30 to 40kVp.

Joe.
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Dennis P Brown
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Re: Nick Babusis Fusor Progress

Post by Dennis P Brown »

I owned a 428 Cobra Jet Mach One Mustang (as a teen) - it was claimed it could go 180 mph. Since it had the engine and suspension, so of course I decided to try - buried the speedometer at 120 mph and had lots of throttle left ... I realized how crazy this was and backed off - likely got to 140 mph before I realized the mistake I was making.

Moral of the story: if you have the power the temptation to use it is overriding - a power supply like that needs proper shielding even if one keeps it under 33 kV. As for 40 kV that is likely going to make that chamber start to become transparent - so shielding is essential.

Bottom-line: one always needs a detector to warn one of any x-ray danger, and fail safe shielding is a mandatory requirement for a good reason. You get one mistake and then learn the hard way why that mistake was so terrible. We lost one amazing contributor to cancer already and through it might have been for any reason, lets not chance it. Shielding is cheap and easy (one need not use lead, either) - there is no excuse not to have it installed. Ditto for safety of others. Proper cable is a good idea as well.

Voltage alone determines the x-ray energy - the current, the x-ray's intensity.

Marking the limits on the power supply scales with red lines is useful as is calibrating the voltage scale so you really do know what the actual voltage the chamber is seeing.

Like lethal voltages, x-rays are unforgiving.
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Re: Nick Babusis Fusor Progress

Post by Nick Babusis »

It seems I should have done a more thorough description of my progress! Hopefully this will allay people's safety concerns:
1. I am not running my fusor at 150kV. My voltage is limited to ~50kV by my feedthrough and I intend to start fusing much lower than that. The 150kV, 150mA rating is for the x-ray machine in <=6 second pulses at a 1% duty cycle. I am not yet sure what it can continuously handle before overheating.
2. I am shielding the viewport with a cup made from 1/8" thick lead. This may need to be modified to use a mirror since the webcam I am currently using is not designed for low-light use and severely compensates the plasma's color. The ceramic feedthrough cannot easily be shielded while preventing arcing, but it is directed upward at my (uninhabited) room. The walls next to the fusor are exterior walls.
IMG-5861.jpg
3. I am monitoring and recording my radiation exposure with a Radex RD1212 dosimiter and a GCA-06W geiger counter.
4. I read up extensively on x-ray machine design and the machine's manual, as well as consulted with a professional radiologist when taking x-ray images.
5. The preliminary plasma ignition test was done at <1kV (current limited) just to see if the plasma would ignite as expected.

High Voltage Cable
I still have some concerns about the safety of my high voltage cable. I am using a 40kV rated cable with a 0.58mm radius conductor encased in a 2.36mm thick silicone layer housed inside a 1.88mm thick vinyl tube. This is certainly an improvement from the "40kV rated" silicone cable I was using before (0.33mm radius conductor encased 2.26mm thick silicone). However, according to my calculations (treating the cable as a cylindrical capacitor with a grounded object such as an ill-placed hand forming the outer conductor), the breakdown voltage of the silicone will be reached at only 40kV. Fortunately, dielectric breakdown should occur from the center of the cable outward, effectively increasing the conductor radius. I will be testing this by wrapping the cable in grounded foil and raising the voltage of the cable (while disconnected from the fusor) and looking for signs of breakdown.

Neutron Detector
I will be performing experiments today to see if my Ludlum model 2000/CHM-11 neutron detector will work. Hopefully I do not have to replace the tube, since I only have 2 weeks before leaving for a summer internship. I will be attempting gamma detection and background neutron detection with different bias voltages, discriminator settings, and series resistor/capacitors.

More updates to come!
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Re: Nick Babusis Fusor Progress

Post by Rich Gorski »

Nick,

Sounds like you've given this project a lot of thought. However even at 30kV your stainless steel chamber will start to become transparent to X-rays. So, keep an eye on that dosimeter and GM counter. Unless your control area (and everyone else) is far enough away you will likely need to install lead shielding around the entire chamber especially if you go higher than 30kV.

If your worried about the safety of your HV cable you can always run it through a length of grounded conduit. Just keep it below say 35kV. When your confident about the whole operation and you want to go higher than 35kV then consider improving your HV cable. You will get plenty of neutrons at 35kV.

Rich G.
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Re: Nick Babusis Fusor Progress

Post by JoeBallantyne »

In my experience you do NOT need to use a series resistor when connecting most neutron tubes to a Ludlum 2200. I suspect that applies to the Ludlum 2000 as well. Some neutron tubes are explicitly designed to have minimal gamma response, I think the Russian corona tubes fall in that category. (The B10 lined tubes are ones that WILL respond to pretty much everything like a normal geiger counter if you run them at too high a voltage - but those are in sharp contrast to Russian corona He3 tubes.)

Bottom line, the fact that the Russian tube doesn't respond much to gamma radiation, does not guarantee it is non functional - it may respond just great to neutrons, as it is designed to detect neutrons, and to NOT respond to gammas. Trying to determine if it works by exposing it to gamma radiation is not the best way to go about it. You should really be using a neutron source, not a gamma source.

This post discusses using a Ludlum 2200 (sister instrument to the 2000) with various neutron tubes: viewtopic.php?p=97981#p97981

The Russian He3 corona tube I tested (SI19), needed a bias of ~2000V, but worked with a pretty high threshold setting of 35mV - in contrast to most of the other tubes, that needed a much lower threshold setting. The tube I was testing did have a series resistor connected to it. I don't recall at the moment what the value was.

Joe.
Last edited by JoeBallantyne on Sun Apr 23, 2023 11:10 am, edited 2 times in total.
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Re: Nick Babusis Fusor Progress

Post by JoeBallantyne »

If I were you, I would simply connect your corona tube directly to the Ludlum 2000, and slowly raise the bias voltage until you start getting background neutron counts registered on the tube - at a rate of something between 1-3 cpm. You might have to go all the way up to 800 +- 50 V to get the tube to count. The SI19 I was using required a bias voltage of ~2000V, but it was a pretty fat tube - at 1 1/8 inches diameter. If your tube is thinner in diameter it may work at a much lower bias voltage than that. IIRC the CHM11 is about 1/2 inch in diameter.

I would just raise the voltage really slowly - like 50V, then wait a minute, and log the counts over that minute, then raise the voltage another 50V, log counts over another minute, etc.

As soon as you start getting any counts, I would only raise the voltage by 25V at a time instead of 50V. Once you are getting something between 1-3 cpm, the bias is probably reasonable, so write it down, and then do a 10 minute run or so, and log the overall counts. If you are getting an average of 1-3 cpm over a 10 minute period or longer, I would call it good, and run your tube at that voltage when you are trying to detect neutrons from your fusor. (You must use a moderator with the detector when you are trying to detect fusor neutrons, but you do NOT need a moderator when you are determining the bias by counting cosmic ray induced background neutrons.)

Mark Rowley posted about using the CHM11 with an unmodified Ludlum 3 counter. Which means the threshold was probably at ~35mV, and the bias was 750V. See this post: viewtopic.php?p=85801#p85801

Joe.
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GSTAR Documentation

Post by Nick Babusis »

I have not yet achieved detectable fusion, but in the interest of providing this information in a reasonable time frame, I am posting all my resources on my fusor, now christened as "GSTAR" (general purpose starter reactor), in the google drive link below:
https://drive.google.com/drive/folders/ ... sp=sharing

Note that this is still a WIP. I have so far spent ~$4,100 over 7 months on this project and expect to spend at least a few hundred dollars more before achieving the project goals.

Other Updates
Work will resume on GSTAR at the end of the summer. No progress on anything other than documentation and neutron detector research (to be posted in a different thread) will occur until then. I have so far done two qualitative runs at relatively low voltage. voltage/current/pressure/neutron flux data will be posted once I begin higher fidelity data gathering. The plasma continues to be very difficult to control due to the positive feedback between the pressure and current, causing me to blow the fuse on the primary variac transformer as shown below.

Steady-state plasma:
Screen Shot 2023-06-23 at 7.18.45 PM.png

Fuse blow, likely caused by thermal runaway:
fuse_blow_trimmed.mov
(3.62 MiB) Downloaded 135 times
Mistakes and Lessons Learned:
  • The current high voltage cable (40kV silicone cable inside 3 layers of vinyl tubing with an aluminum foil shield) produces a lot of corona hissing and may not be safe. This will be replaced with a modified version of the HV cable that came with the x-ray machine.
  • My neutron detection circuit is likely incorrect (in-depth explanation will be posted in the neutron forum).
  • I forgot to take the oxygen port cover off of the PEM cell when plugging it in, causing it to be launched off of the oxygen port after a few seconds of operation. There does not appear to be any significant reduction in D2 production rate.
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Re: Nick Babusis Fusor Progress

Post by Richard Hull »

Very nice star in your proto fusor. Demo for now.

Learning to control the current/voltage/pressure combination is just another art form that must be mastered among the science that is the fusor.

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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