My progress II

For posts specifically relating to fusor design, construction, and operation.
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Richard Hull
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Re: My progress II

Post by Richard Hull » Fri Sep 28, 2018 5:01 am

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
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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Eduardo_Machado
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Re: My progress II

Post by Eduardo_Machado » Mon Oct 22, 2018 9:10 pm

Hello,

Just to update. We just received a 25L deuterium lecture bottle.
IMG_1584.jpg
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

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Eduardo_Machado
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Re: My progress II

Post by Eduardo_Machado » Sat Nov 10, 2018 8:43 pm

I got more stuff for my fusor.
IMG_1589.jpg
IMG_1613.jpg
IMG_1609.jpg
IMG_1610.jpg
IMG_1612.jpg

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Dennis P Brown
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Re: My progress II

Post by Dennis P Brown » Sun Nov 11, 2018 12:18 am

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.

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Re: My progress II

Post by ian_krase » Tue Nov 13, 2018 6:20 am

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.

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Re: My progress II

Post by Eduardo_Machado » Sat Dec 08, 2018 8:59 pm

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


fusor 2.jpeg
fusor1.jpeg

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Richard Hull
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Re: My progress II

Post by Richard Hull » Sun Dec 09, 2018 9:40 pm

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
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.

Robert Dwyer
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Re: My progress II

Post by Robert Dwyer » Sun Dec 09, 2018 11:19 pm

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.
If we throw more money at it, it will have to work... right?

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Dennis P Brown
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Re: My progress II

Post by Dennis P Brown » Mon Dec 10, 2018 1:11 pm

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.

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Re: My progress II

Post by Eduardo_Machado » Mon Dec 10, 2018 2:43 pm

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

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