Archived - First Star mode & Setup

[UUfusoren]

Today we achieved star mode for the first time! We used Argon. Pictures are taken at 21 kV, 20 mA discharge.

We also have a picture (the third one) of the grids at 30 kV, pressure lower than 10^-6 torr. here we can see that the ceramic is glowing (pink and blue). We cannot find an explanation for this (the ceramic has already been outgassed), does anyone have any ideas?

Greetings from Utrecht University



EDIT: I understand this is the way to add new pictures (we should edit the first post and not reply with more pictures, or should we do it differently?)

Here you can see our complete setup (various power supplies and measurement apparatus on the left, the chamber above the diffusion pump in the middle and a mechanical pump on the right at the bottom).

Then there is a picture of our He3 neutron detector with its paraffin casing.

Finally a picture of the interior of the chamber with the filament glowing.
Those are the most important parts of the setup. We hope to get started on Hydrogen next week and on Deuterium in 2 or 3 weeks!

As to the materials of the grids, the outer grid is stainless steel, and the inner grid is tantalum.



EDIT: Now with newest pictures of the setup, and hydrogen plasma!
Is it a good idea to have all the pictures in a separate post to save time (as Steven Sesselmann proposes)?
Should some pictures be taken away, and if so, which ones?

Greetings to all,

Benjamin Brenny, speaking for the Utrecht University group

[Frank Sanns]

That is fluorescence and electron beams. This happens as the pressure is around 12 microns or a little lower and the voltage is >20 KV. You can see also a hazy appearance on your viewport which is the same as what is spilling onto your outer grid and insulators. I hope your are not near your viewport when you are operating as in the last photo as the x-rays are most likely >1R/hr.

I have an aluminum outer grid and it will glow red under these conditions. Patterns can be changed by moving your outer grid around. Those with the fusor as there outer grids will never see this effect.

Frank S.

[Carl Willis]

Hi Benjamin,

Very pretty and professional construction. The outer grid reminds me a bit of the U. Wisconsin machines.

Your big window is fine for low-power operation, but will need to be replaced with metal when the power and voltage come up or you'll likely break it from thermal stress.

The glowing is definitely fluorescence caused by electron bombardment of the ceramic and the presence of various rare-earth oxide impurities in it.

Welcome on board, and I look forward to seeing more reports on your effort.

-Carl

[UUfusoren]

We used a radiation monitor to check, and indeed the radiation is as high as 0.2 mSv/hour at ten centimeters from the viewport. We are using lead to shield us from the radiation.

Thank you for your kind words about the design. I attached a picture of our grids, when not in the fusor. The O.D. is 12 cm, the I.D. is 4 cm. There have been some minor changes since the picture was taken. As you can see in the pictures posted before, the stand-offs are now entirely ceramic.

We have had our inner grid at 420 W (20 mA, 21 kV) so far, under which you couldn't lay your hand on the fusor because of the heat, but the viewport held fine. Our max is at 600 W (20 mA, 30 kV), and you think the window should be changed for a metal plate? How large could a window be under those conditions? Maybe we've got a smaller window on a 6" flange. We really want to avoid breaking the window!

Regards, Benjamin

[Richard Hull]

Great work Benjamin! I will add your name to the Plasma club list. I note you said "we" in your original posting as if other are involved. Would you rather have your University's group credited?

I am stunned that no one suggested UV light as creating the ceramic glow. Argon glow lamps have long been used for UV emission sources. Yours would be at "vacuum UV" levels and wavelengths. Electron beams are certainly also possible, of course. When using deuterium in a real fusor, You will once again have a superior and intense source of UV as deuterium lamps are also used as UV sources. Many calcium based and rare earth compounds glow red under short wave UV.

Good luck on taking this fine looking system on to do real fusion.

Let me know how you wish the credit to read.

Richard Hull

[UUfusoren]

I use we because we are a group of six undergraduate students, who are working on this project. But when I created the profile it seemed easier to just use one of our names.

So it is not necessarily me who posts, but it will always say Benjamin. Should we change this?

In any case, the credit is for our group: Sander Mann, Dick Abma, Thijs Krijger, Nivard Kagie, Remco van den Dungen and Benjamin Brenny ( with help from our supervisor Wim Westerveld and other technical staff). Analog to the "University of South Florida senior project group" I think that "Utrecht University undergraduate project group", maybe with our names added, is good. The university should be mentioned, since we've got all our materials from the dungeons here. Nonetheless it is still an amateur project.

In any case thank you for the comments and suggestions. Richard, in the third picture there is no argon in the chamber yet. That's what bothered us too!

Also, if I want to add some pictures of the entire setup, I should edit the first post and add them there, or should I make a new thread?

Many thanks,


Benjamin Brenny

[Wilfried Heil]

Very nice and well designed construction. You've got on of the best setups around!
What material did you use for the grid?

The luminosity from your insulators looks like UV fluorescence to me as well as ion or electron bombardment in certain brighter spots. You could easily move these around with NIB magnets from outside of the chamber.

[Dustinit]

Looks like an Awesome machine.
I hope to see some bubble reports in the future.
I have also noticed the fluorescence and initially was concerned it was X ray
fluorescence. It was most prominant on the tin lead solder connections but not on
the tinned copper wire.
Inerestingly on yours it seems on the outer shell it may be due to UV or elecron bombardment of the flux residue on the outer shell cross points. It looks as if it was perhaps burnt away from the joint itself but not where it wicked away from the joint.
It is probably calcium fluoride (fluorite) which is a common flux for iron and steel and fluoreses blue under UV.
Cool.
Dustin

[Steven Sesselmann]

Benjamin,

Compliments on a nice clean project. With a carefully constructed experiment like this, you are guaranteed to have success.

I too look forward to the results of your future experiments.

Nice He3 detector, but the group is now demanding bubbles as the primary proof of neutrons. It will be useful when you have calibrated it to a bubble detector.

PS:
As for your questions on uploading pictures, I suggest a new system for everyone.

Create your first new post with text only, then create a reply immediately after with the pictures. This will save download time every time we go to read the future replies.

Steven

Bee Research Pty Ltd

[DaveC]

Benjamin and your Utrecht fellows..... well done. Interesting design, neat and clean. And... that is one verrry impressive diffusion pump!!

At your low test pressures, the glow is almost certainly due to Xray and or electron bombardment. Although there will be some deep UV emission from residual gases.

I must add my caution to Carl's about the large window and possible spot heating from electron bombardment. But a small window, somewhat dampens the excitement of seeing all the activity when the voltage comes up.

So, one practical approach might be to use a protective glass plate inside, in front of your viewport, which can take the burden of localized heating, and the metal evaporation and sputtering which will come when fusion is attempted. I would recommend fused quartz, suprasil, or at least borosilicate glass. This will be nearly indestructible up to at least orange heat.

For Xray protection,simply put a good thickness of leaded glass outside your window.
We have used leaded glass windows under vacuum successfully, but I personally am always uneasy about them Leaded glass is quite brittle.

I look forward to more of your group's work.

Dave Cooper

[UUfusoren]

Thank you all for your comments, they were very helpful. We have now made some changes to the setup, see the post in Fusor Construction & Operation: viewtopic.php?f=6&t=2817#p12327

Benjamin Brenny