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
Posts: 11
Joined: Wed Aug 29, 2012 12:55 am
Real name:

Re: Grid Shielding - Testing with Results

Post by davidgrzan » Wed Feb 27, 2013 12:15 am

I think I get what you are saying. Basically if there is more current being drawn there will be more ions, making the grid heat up faster. But more ions means more fusion, helping efficiency.

On another note, I was moved up to the regional JSHS (Junior Science and Humanities Symposium) for my research paper and will be competing there in April.

davidgrzan
Posts: 11
Joined: Wed Aug 29, 2012 12:55 am
Real name:

Re: Grid Shielding - Testing with Results

Post by davidgrzan » Tue Mar 12, 2013 1:44 am

Are there any simulators out there that could replicate the setup I have here with the magnets? I've tried using a few ones found on the internet but they don't have the flexibility of making something similar to this. I think it would help a lot to try different things on a simulation before implementing them in my demo fusor. I found equations for the B field of the magnet at a distance extending from the poles but not from any other point around the magnet and the lorentz force equations. I didn't have any luck with determining the ion's path with the equations I found though.

I did notice however, that the magnets behaved very similarly to solar wind hitting the Earth's magnetosphere. The magnetic field traps the charged particles creating that protected "zone" seen in the first picture and in my setup. Where the solar wind enters the cusps in the picture can also be seen on the magnets in the fourth picture.

I did another test with a tighter arrangement of magnets. The next two pictures shows the visual results (it looks white because of something burning off of the metals which usually goes away after a few runs). I figured that if I moved the magnets closer to the grid wires, the magnetic field would be strong enough to get that zone around the wires. The area void of plasma seems to hover just outside the grid wires though. I'm thinking it's because of how fast the ions are moving at that point or because the plasma needs to act as a conductor. Does anybody know the exact reason of this?

I'm thinking about insulating the magnet holding apparatus from the grounded plate and testing this method at a lower voltage next. Any suggestions are welcome.
Attachments
IMG_0775.jpg
IMG_0775.jpg (416.8 KiB) Viewed 2309 times
IMG_0773.jpg
IMG_0773.jpg (399.5 KiB) Viewed 2309 times
SolarWind.gif
SolarWind.gif (146.62 KiB) Viewed 2309 times
IMG_0771.jpg
IMG_0771.jpg (363.79 KiB) Viewed 2309 times

User avatar
Chris Bradley
Posts: 2930
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Grid Shielding - Testing with Results

Post by Chris Bradley » Tue Mar 12, 2013 8:07 am

There is a programme called Maxwell which is free as the Student Version ('Maxwell SV'). It will do 2D DC fields.

However, if I may ask whether you have a main objective, or is it just to 'look around' and understand a bit more about plasmas near magnets?

The reality is that a configuration such as this is not likely to improve a fusor. The reasons are that
a) what you are seeing as glow discharge are the trapped electrons and slow ions, whereas fast ions will scoot straight past those magnetic fields almost as if they were not there, or worse still they are deflected as they slow down and reverse direction, leading to drifting out of the area of maximum electric field potential,
b) field lines from solid magnets always start and finish at the magnet, so any charged particles will flow 'along the field lines' and intersect the magnet, which will heat it up markedly and result in the biggest losses.

As has been speculated above, what you may be doing is simply diverting losses from one place to another by redirecting those electrons.

The presence of magnets will cause higher levels of ionisation, as you have mentioned, but it is not easy to understand where, in the voltage potential gradient, those ions form. This is important because it will determine the peak energy of the ions once accelerated. With magnets, you will also be able to continue with a glow discharge at pressures lower than without, which again is due to the trapping of electrons rather than their 'immediate loss', although they will still be lost in quick order once they work their ways along the field lines to the magnets. Lower pressures mean fewer fusible collisions, in time.

Plasmas are unpredictable at the best of times, though, because of all the potential complex interactions (electrons follow ions, then the ions follow the electrons, like a big conga dance, then some drop out of the dance while others join). So you will never get bored with trying different arrangements, and maybe you'll find something unexpected.

davidgrzan
Posts: 11
Joined: Wed Aug 29, 2012 12:55 am
Real name:

Re: Grid Shielding - Testing with Results

Post by davidgrzan » Wed Mar 13, 2013 12:38 am

Chris Bradley,
Thank you for the simulation idea I will download it soon. To answer your question, the experiment was to test different methods of shielding the grid from ion impacts. The magnets were supposed to create an area void of plasma around the grid wires, decreasing the amount of collisions. It obviously had some problems like you mentioned above unfortunately.

Even if I could get a little less heating to the grid at lower voltages I would have to conclude it to be not worth implementing in a real fusor.

I insulated the apparatus and the pattern became much more clean so I took another picture for those who want to see. The zones which are hovering outside the grid wires are more noticeable in this picture too.
Attachments
IMG_0781.jpg
IMG_0781.jpg (302.23 KiB) Viewed 2309 times

Post Reply