Ion Steering Fins - Experimental Results

[Tyler Christensen]

I was playing around in Poission Superfish and came up with a geometry that I thought should steer ions to avoid grid wires. Apparently this idea has come up before, also (Steven pointed me to this old discussions: viewtopic.php?f=14&t=6580#p44586)

First of all, unfortunately one of the fins desoldered itself so I don't have much in the way of actual quantitative results. This means I didn't get a chance to do much conditioning, and don't have numbers to provide so you'll have to just take my estimates as what they are.

When running at 20kV 15mA, I estimate the neutron output of this unconditioned state to be 5x higher than the fusor running at 20kV 15mA, conditioned, with no ion guides (also highly outgassing on all that new surface area with plasma present, so gas purity was not good at all).

I also noticed that for a given voltage and current rating, the grid wires seemed to be keeping a much lower temperature than at an equivalent power without the ion guides. They still glowed, but not to nearly the same degree.

When I pushed it up to 40kV it was very unstable due to extreme ion-induced outgassing, so I couldn't really get a good feel for neutron output, but I did notice that my camera was exhibiting far less static due to x-rays, so maybe somehow x-ray emissions are lower.

Unfortunately I don't have much more in the way of results to provide beyond that since it melted itself, but I would be very curious to see someone reproduce this with access to the resources to cut the pieces out of stainless and TIG the whole thing together (maybe you'll manage to 10x+ your neutron numbers!). I'll probably make it in stainless when back at MIT but I won't be able to try it until July/August when I'm home again.

Photos:
1. E-Field simulation. Although this isn't an actual cross section found in my fusor, I think it is a pretty good 2d representation of the fusor for modeling purposes.
2. Soldering the grounded-fin assembly
3. All installed in the fusor
4. Showing the alignment with the grid
5. Operating at 20kV 15mA
6. Operating at 5kV 25mA after one or two fins fell off (haven't opened up the chamber to check the exact damage yet). As can be seen, the grid wires where the ion guides are still in place are running much cooler.

[Mike Beauford]

These are in line with what others like Doug Coulter had done with his cylindrical fusor.

Nice work!

[Richard Hull]

I think, I would have put the blades between the grid wires rather than in line with them, (geometrically speaking). High field emission would be at work here.

Richard Hull

[Doug Coulter]

I have yet to get better results with vanes and fins than without, so I shelved that one for awhile. I'd thought with vanes I could get a better focus, and had made the cardinal mistake I sometimes call others out for - what about the electrons? And other assumptions that turned out to be bad ones. Or at least *seemed* to be bad ones. A grid I made with ceramic rods shielding the wires from direct hits from outside was just horrible in operation, and harder to keep "lit" as the secondary electrons from ion hits weren't present anymore. It's a big parameter space, and I think we've got a lot more looking to do at any rate.

That U of Wis paper shows a lot of fusion outside anything that could be called a focus...hmmm.

Looks like I need to continue to explore this space, now that I have far better gear and it's not so difficult.

Yes, solder won't live in a fusor - and it even gives off lead and tin vapor when not molten. Probably you need to weld or use a high temp braze there. And short runtimes!

[Steven Sesselmann]

Tyler,

Well done on the quick execution of this experiment, you didn't waste any time between idea and actual experiment.

I still think the idea has merit, and that someone with a spherical fusor should try welding in some steel baffles. As mentioned, I would also add an equatorial baffle.

Hiding the grid in the shadow of the baffles makes perfect sense to me, as it should minimize ion impacts.

No reason why the grid could not be constructed the same way, with flat fins.

Keep up the good work...

Steven

[Brian_Gage]

Tyler,
I can't see your pictures, but what I've read clicked today as I was reviewing a post on Doug Coulter's S/E/T forum. It was a post by Steven Sesilman (Austrailia, may have his last name spelled wrong) about a different concept in fusion, aligning the ions to create optimum conditions for fusion, since ions want to fuse like "water wants to run downhill", and not by smashing them together. He suggests that the right conditions of alignment happen in IEC more by accident than design. As your post and his met, I wondered if your use of vanes were also creating this kind of alignment with some success. Don't know if you have corresponded with Steven, but it seemed worth suggesting a meeting of minds?

Regards, Brian

[Frank Sanns]

Nice work Tyler!

I have been pondering this there are several variables that have changed with your design. It is not just baffles that limit the ions. It is increased surface area of the outer electrode which I can say helps. The distance from the outer electrode is now not fixed. This provides a multitude of acceleration points and limits circulation from spherical to figure 8s with the node in the center. Clearly keeping velocity high while the ions change direction will conserve energy while obeying conservation of momentum. Interesting experiment but with every experiment done, more are thought of. Good job.

Frank Sanns