Grid Shielding - Testing with Results
Posted: Sun Feb 24, 2013 12:28 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.
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.