Grid Shielding - Testing with Results

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
davidgrzan
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Grid Shielding - Testing with Results

Post by davidgrzan » Sun Feb 24, 2013 5:28 am

Today was the award ceremony of the regional science fair I competed in so I decided to share what I found during my research. I built a demo fusor and tested grid shielding methods as it was one of the few areas that could be tested without fusion occurring. I received a couple awards and was selected as an alternate for the research paper category but was not selected for the project category. I guess I was slightly disappointed that I didn't get to move on to the next stage because the judges and people there seemed to be very interested in it which got my hopes up.

I wanted to use the anode to deflect ions from impacting the grid and while searching through the forums, I found that Steven Sesselmann had came up with a good idea, using baffles lined up with the grid wires to deflect the ions along its whole path. I constructed it and cranked up the voltage to see if it had any visual differences compared with the control (you can see it in the first picture). The control grid is just a regular copper tubing grid with three loops. To test the temperature of the grid quantitatively, I came up with the idea of attaching solder to the grid to see how long it would take for it to melt. Given the melting points of the soldering wires, I could compare how the control and shielding methods worked.

Control time to reach 577 degrees Celsius: 101 seconds
Plate or baffle method: 87 seconds

The control worked better as the inner grid had a slower rate of heat transfer. I think the plate method heated up faster because of the stronger electric field in between the cathode and anode. This would cause more field emission or electrons coming off of the cathode and heating it. The plates could be deflecting ions but it still is wasting energy on heat.

The second method to shield the grid is one I came up with. I decided to try to use neodymium magnets to distort the plasma around the grid wires so that almost none of it would impact the grid. You can see the pattern of the plasma caused by the configuration of magnets I chose in the second picture. It was distorting it how I wanted but the grid wires were now in the zones that were void of plasma. This means that the ions were still heating the grid and the results showed that.

Control time to reach 577 degrees Celsius: 101 seconds
Magnetic field method: 62 seconds

I ended up trying to move one of the magnets closer as I could not move all of them closer because of the way the apparatus was set up and of how strong the magnets were. You can see the picture of the righter most magnet being moved closer to the right part of the grid (picture 3). It is at a lower voltage and the plasma can be seen going around the grid wires. Increasing the voltage decreases the zone where there is no plasma to outside the grid. No matter where I put the magnets, the zone void of plasma hovered just outside the grid (at the higher voltage, 7kv, that I was doing the tests with). I tested it anyway and the magnet that was closer did better than the magnet that was farther away.
I hypothesized that with further tests, if stronger magnets were moved closer to the grid, there would be a decrease the rate of temperature change.

Basically that's just a brief summary of the important results so if any of you have any questions I'd answer them or if you found something I might have missed or done wrong let me know. I'm most likely willing to do another test if you have a suggestion.

Also I'd like to add that this forum and the people here were very helpful to me when doing my project and I thank you guys for that.
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lowervoltage2.jpg
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plates3.jpg
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Tyler Christensen
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Re: Grid Shielding - Testing with Results

Post by Tyler Christensen » Sun Feb 24, 2013 5:38 am

Was cathode current relatively unaffected between control and test? If it was affected, since you were running constant-voltage it sounds like, you might want to normalize the times to wattage. I wonder if that would change the outcome.

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Dennis P Brown
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Re: Grid Shielding - Testing with Results

Post by Dennis P Brown » Sun Feb 24, 2013 12:04 pm

Extremely good experimental work and a really clever approach to non-fusion work. I'd love to see your paper. Sorry you didn't move to the next stage but as an experimenter you really demonstrated fantastic abilities.

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Jim Kovalchick
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Re: Grid Shielding - Testing with Results

Post by Jim Kovalchick » Sun Feb 24, 2013 12:21 pm

Trying something new is important, and you should be proud of your work. The reality of science fairs often means that adventurous but non-mainstream projects suffer in the judging. Putting cow poop in a bucket and observing it give off methane while claiming that it is green energy will often beat nuclear fusion depending on the judges. Last year, my son's neutron producing fusor made it to ISEF, but only after narrowly winning his high school fair to a project that tried to use rotten pumpkin rinds as a water filter. The pumpkin project, which was well written, came across as very 'green.' A fraction of the judges will understand your work. Don't let that part ruin your accomplishment. Very few students are willing to step up to scientific challenges like you have. Be very proud of yourself! Congrats and well done.

davidgrzan
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Re: Grid Shielding - Testing with Results

Post by davidgrzan » Sun Feb 24, 2013 7:40 pm

I've attached my research paper if anyone wants to see.

In response to Tyler Christensen, I set up a voltage meter but not a current meter. So are you saying that the temperature of the cathode affects the current if I were to measure it? If that's the case it would be a great way to measure the temperature indirectly.
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Effects of Cathode Shielding Methods in an Inertial Electrostatic Confinement Fusion Reactor 2.pdf
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Dennis P Brown
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Re: Grid Shielding - Testing with Results

Post by Dennis P Brown » Mon Feb 25, 2013 1:05 am

Just skimmed through your paper - very impressive. Thanks for putting it up. I think a number of students should read this for a "How to do a good research study" and writing up the results. I hope to have time to read it in detail later this week.

Tyler Christensen
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Re: Grid Shielding - Testing with Results

Post by Tyler Christensen » Mon Feb 25, 2013 1:37 am

Not the temperature affecting current. My thought is what if the shields or magnets affect the current draw (which it probably does). I don't have time to read through the paper right now, but it looks like you concluded your ideas failed to improve confinement because the grid got hotter even faster. But what if the magnetic system draws four times the current of the control. Then it actually would be dramatically helping confinement away from grids, per watt, even though the grid heats up even faster due to the higher wattage.

kcdodd
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Re: Grid Shielding - Testing with Results

Post by kcdodd » Mon Feb 25, 2013 2:16 am

If the magnetic field is mostly trapping electrons, making a better ionizer.

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Dennis P Brown
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Re: Grid Shielding - Testing with Results

Post by Dennis P Brown » Mon Feb 25, 2013 1:47 pm

Really liked your method to measure temperature - highly creative! Sometimes lack of money works in very novel ways.

Can't help if an experiment produces somewhat mixed results - that is science. Very clear, well written paper and logical - as the saying goes: say what you mean and mean what you say. That works. Following an outline like you did pays. You should be proud of your research and the paper - few in HS do such excellent work.

ab0032
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Re: Grid Shielding - Testing with Results

Post by ab0032 » Tue Feb 26, 2013 12:34 am

How beautiful.

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