Fusor Forums

These are the components to the next fusor. My last fusor had a glass chamber, but my new one will be a 2.75 ss 4 way cross.

My Cf 2.75 4 way cross arrived. My next step will be replicate the plasma I achieved in my glass fusor (viewtopic.php?f=18&t=12427) in this new setup.

A lot of work till I get to the fusion.

Hi, I'm 11, and I was wondering where you purchased your 4way cross, because as little information as I can find for steel-hemisphere fusors, I can find almost nothing about the construction of a cross. Any information you could give would be much, much appreciated.

Thanks
Jonathan
www.youtube.com/nitrojonscience/

Conflat crosses and Tees are found ready made. Thousands are made and sold each year and have been for half a century. Virtually no one makes there own crosses of Tees. They come in many industry standard sizes. Most of us here buy them off e-bay or at surplus houses.

Richard Hull

Jonathan,

There are several places. The best I have found in terms of cost is here https://www.ldsvacuumshopper.com
You can also look at Duniway Stockroom.
Ebay might have better deals though.

-Matthew

Hello Jon,

I am Eduardo's father and I am helping him in this journey. I bought him this conflat cross at E-Bay ($50) and the seller sent it to us hear in Brazil.

You can search "2.75 cf 4 way cross" and find many suppliers. I believe a cross fusor is easier to work and cheaper than a hemisphere fusor.

There are many F.A.Q.s here that can help you to figure out what is better for you. I suggest you to search the posts of Neutron Club Admission Request and study the fusor people used recently.

Good luck on your project.

Cristiano

Thanks guys, I'll check those sources out!
Jonathan

Hello Jon,

I am from Brazil and I'm 10 years old. I bought my chamber at Ebay, there you can find a lot of stuff for your project.

I saw your channel on Youtube and I subscribed it, I liked and want to follow your videos. Its good to have another kid around here.

Nice to talk to you,
Eduardo

Hi Eduardo
Quite happy to discover another kid around here too!
Thanks
Jonathan

Also, found this 4-way cross here: https://www.mdcvacuum.com/DisplayPartRe ... r=EU&d=MDC
At 182 USD it's quite costly but I'll take it. Does anyone else have a better place?

I saw a four way cross go for $40.00 at last years HEAS flea market. It was sold surplus by the Univ of Maryland team that came down to sell all manner of vacuum gear. This is low a price is rare, but e-bay has seen them go for $60.

I picked up a 6 way 2.75 cross at last year's HEAS flea market from the Univ of Maryland guys for $30.00!!! It was when they were packing up and went crazy yelling, "Everything half price or make and offer". I dove in and bought over $100.00 work of stuff. You can see it all at

viewtopic.php?f=18&t=11727&start=20

My vacuum haul of stuff is near the very bottom of the page

MDS is a great company to do business with, but their items are new and not surplus, thus, the higher price.

Richard Hull

Hello,

Just to update. We just received a 25L deuterium lecture bottle.
We already ordered a turbo molecular pump and some parts. I believe next month I will be able to run a demofusor (12kV / without deuterium) in this setup.

If someone want to see my last fusor:
viewtopic.php?f=18&t=12427


Regards,

Eduardo

I got more stuff for my fusor.

Impressive. Good start. Don't forget, neutron detection is also required for a real fusor. Also, a gate valve is needed to "throttle" the turbo so your deuterium isn't used up in just a few runs.

I would like to add that one can often "chop-shop" tees and crosses together using an inexpensive Mapp Gas blowtorch and silver brazing compound.


There are lots of cheap vacuum components on Ebay that were made for some specific machine. To the casual user, they are of little use, very strangely shaped usually and with mismatched ports and flanges.

It's not hard to hacksaw the extraneous flanges off and then braze on the appropriate "socket weld" flanges -- however, you must be conscious of the limits to doing this. In particular it is difficult to braze large Conflat flanges unless they are the rotatable kind (where the small sealing flange is separate from the large, heavy bolted collar).

A fusor will have the following points of penetration on its chamber:

- Viewport (full size)
- Pump (full size)
- HV feed through (full size)
- Gas inlet (small tube)
- Roughing port (small/medium tube, very very optional)
- Vent port (small/medium tube, very very optional)

Etc.

A tee only has three large ports. One can easily drill a hole and braze in a small Swagelock connector to provide gas inlet, for example.


Also note that they sometimes sell flangeless weldable tee and cross bodies, though these are not normally economical compared to just buying complete tees on the used market.

Hi, today we started the first test of the fusor, it is almost complete. Still need to finish the deuterium line, the tension and current measurements and buy a 40 kV transformer. Now we are using a neon transformer of 12 kV.

On the first try, it was not very good. On the second try the plasma ignited at 30 microns, but we couldn’t maintain the plasma with pressure below 70 microns. That happened a lot of times.

Somebody could give a suggestion how to improve the plasma at pressures bellow 70 microns?

Thanks,

Eduardo

How long did you operate it? Looking at your set up, It looks like you can seal your system off between the fusor and the pump with a valve. I suggest pumping as low as the pump can go and read the pressure. Record the pressure. Next close the valve and read the pressure rise and write it down every ten seconds. How fast does it rise?

Some times you have to glow clean for 30 minutes and let the fusor get hot while leaving the pump running. This will outgas (pump out) a lot of trapped gas.

Richard Hull

It looks like the plasma may be heating the chamber walls and cause outgassing which explains the pressure spike.

I will say that when I operated my fusor which was made from a 4-way cross I could not have a stable plasma below 30 microns.

I tried my hardest to get my pressure as low as I could as I had the theory that at my voltages the neutral/ion collisions at high pressures kept me from increasing my fusion levels. My most stable operation and greatest fusion yield (pitiful compared to others on this forum)was at 50mTorr. I only ever once was able to maintain a plasma at 18mTorr, and that was for about 3 seconds! My theory is that because the cathode is so close to the chamber walls in smaller fusors, they sit on a weird spot on the paschen curve. I also found that at 50 mTorr at 50kv the beam formation was far better looking than at 30mTorr (the lowest pressure I could operate at).

Just thought I would add my experience with maintaining the discharge in a small fusor.

Do know that large chambers can create stable plasma's at lower pressures then small chambers; for instance, I could create a good plasma from 3 to 12 microns in my large chamber. When I halved the volume, that pressure for a stable plasma increased to the range of 10 - 24 microns (below 10, the plasma would not ignite.) Running a plasma to clean the chamber is essential and can require a number of runs with unstable results. I have to "season" (ignite a series of brief plasma's) in my chamber before I can obtain fairly stable operation.

Heating of the walls is a good thing - people even use heating tape to do this (under high vac) to first clean their systems before use. Seasoning is also about bringing up chamber wall temp to help drive off water.

It is rather important to first get your chamber in the low 10^-4 torr (low 10^-5 torr far better) to clean the system. Only then, do I throttle down my gate valve, fill with deuterium, and season my chamber in 5 - 10 micron range (best range for my size chamber) before trying to create a stable plasma. During that time, my current runs away and the plasma often disappears, as well. Having a clean chamber after it has been exposed to air (water vapor!) is important. I am not aware of any successful fusor that doesn't manage to do this (that is why a turbo or DP is essential; I am sure there is someone who has managed to be the exception but that isn't something a newbie should aim for with their first fusor.)

As Richard suggested, check your system for leaks/virtual leaks doing as he instructed. If your system is leaking, you are not going to get stable plasmas. Pressure of 70 microns with a good pump are just too high (ditto for 50 microns.) Something isn't right if you can't get below 10 microns using your pump (there are leaks and/or bad pump and/or gauge.) After doing what Richard suggested, post the results and we could offer further help.

Hello,

Thank you for help. The lowest pressure was 4.2E-4 torr. We measured the increase, and in one minute it increased from 10 to 20 militorr. Is it good?

In my next try I will get more precise measurements and try to get plasma during 30 minuetes to clean the chamber.

Do you think a smaller grid could improve the low pressure plasma balance?

I want to better control this part before add deuterium to the system.

Regards,

Eduardo

Going from 10 microns to 20 microns in a minute could be normal out gassing from the chamber (i.e. a virtual leak.) Letting the system stay under low pressure ( 4 *10^-4 torr) and heating the chamber should drastically lower that rate. Running a plasma will help as well. Are you using a turbo or diffusion pump? That isn't very low for those devices. Something does not appear correct.

Hello Mr. Brown,

Thank you for your suggestions. I am using a turbo pump. I believe one of my gaskets isn't very good, I will change it and heat all the chamber to see what happens.

Regards,

Eduardo

Hello,

I have been working on my Fusor (it was named Kelvin II) and I have a lot of improvements. It is almost complete to produce neutros.

I would like to share my progress in my neutron detector. I change some emails with Mr. Bob Higgins and I am using his paper (viewtopic.php?f=31&t=10971&p=72635&hili ... ins#p72635) to assembly my detector and Mr Bob is kind off a mentor to me in this part, but I will also use a bubble detector as a counter-proof.

In this video, I open the package we received from Bob.
https://youtu.be/O865PyiZznk

Some parts I am using:
Edwards Ext225H turbo molecular vacuum pump, with homemade controller, based in the schematics (viewtopic.php?f=10&t=11057&hilit=edwards+controller)shared by Mr. David Kunkle (Thanks Mr David). Vacuum chamber. We already test it, but I need to change my feedthrough to a high voltage one (arriving next week). Micrometer Valve and needle valve (swagelok). Vaccum Gauges: Mks901p, with homemade controlers, I used Mr. Finn DIY controller model (Thanks Mr Finn).
Deuterium gas: Cambridge Isotopes, 0.5 VA variac and Ballast 68K 100W resistor, already posted photos of it in previous posts.

This is me, running a test with Kelvin II before the assembly of deuterium line.
Now, I am using my 12kV Neon transformer to test and outgas my chamber. I could achieve stable plasma at 19 microns 5ma. In the photo bellow you can see a test. You will see I have a non conventional grid, that I made after some advises posted before. I can't get a star, but it is working well, and it is much easier to build and produce a stable plasma in my chamber, compared to my geodesic grid.
Voltage measurements, 50Kv x-ray transformer and lead shield will arrive next week. I hope I can post a detailed photo of my complete setup next week. I hope I can get some neutrons this month.

Remember, 50 kV can and will produce a strong and very dangerous x-ray stream. Be certain you can measure that hazard as well - did you calculate the required lead thickness? Be certain the shield size is large enough to provide full protection to all body parts when the fusor is operating - don't overlook the lower body. A mistake can lead to serious long term increase in cancer risk - chronic exposure can lead to death. Lead is dangerous to handle (wear gloves and wash hands) and dust from lead inhaled is also bad - especially for young children. At least paint any exposed lead surfaces. Maybe make a frame to hold the lead. Lead is very conductive so be careful in placement near the high voltage leads.

Hello Mr Brown,

Thank you for your advise. I used the Barrier Calculator from University of Toronto (https://ehs.utoronto.ca/our-services/x- ... alculator/) and got a 0.83 mm thickness, but we are planning to use 1.0 mm and in some parts 2.0 mm. My father will work with the lead, since I am not allowed to do this. Also, we are studying a setup to use water with borax to shield neutrons.

We are planning to use this fusor to promote science in schools in our community, so we are going to build a nice frame to it.

Regards,

Eduardo