Plasma confinement

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

Moderators: tonybarry, MSimon

Endersworld
Posts: 19
Joined: Sun Jan 22, 2012 10:25 am

Plasma confinement

Postby Endersworld » Sun Jan 29, 2012 9:26 pm

I recently used a magnetron to convert MAPP gas to a plasma. I want to build a magnetic confinement chamber to support it in. This is what i was planning: http://i40.tinypic.com/2zqdel5.jpg.

There could be gaps in the magnetic field, i'll be able to better tell when i fire the machine up

Heres the plasma we have made: http://www.youtube.com/watch?v=psJ8H_-54EM

If i manage to capture the plasma i will Start compressing it with magnetic fields, possibly fusing. Im not certain of the power reqirements as of now, the sphere on this one should be about 4 inch diameter.

How would i introduce a fuel like deuterium or protium or even lithium?

kcdodd
Posts: 722
Joined: Tue Jun 03, 2008 3:36 am
Location: Austin, TX

Postby kcdodd » Sun Jan 29, 2012 9:45 pm

I would not use any gas that is so flammable and it is best to use an inert gas like helium if possible for safety reasons. There is not any reason to use a flammable gas. The only reason deuterium is used is because of the nuclear reactions, not chemical.
Carter

Endersworld
Posts: 19
Joined: Sun Jan 22, 2012 10:25 am

Postby Endersworld » Sun Jan 29, 2012 10:03 pm

I used MAPP beacuse the microwave has an easier time converting flame to a sustained plasma, to use something inert i would have to first arc through it for the initial plasma. The magnetron seems better at sustaining plasma than creating it.

I could always convert H20 directly to plasma, and inject it into the sphere. not sure what the O2 would do in there though, perhaps just make it hotter.

kcdodd
Posts: 722
Joined: Tue Jun 03, 2008 3:36 am
Location: Austin, TX

Postby kcdodd » Mon Jan 30, 2012 3:04 am

Cut a small piece of wire at 1/4 microwave wavelength: ~ 1.2 inches. Put it at the bottom insulated from ground and it will arc plenty to create plasma for you.

Also, could you explain your chamber a little more? As in, what is the desired magnetic geometry?
Carter

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Postby D Tibbets » Mon Jan 30, 2012 3:26 am

Water would make a mix of ions and neutrals (H2O). Unless you have a very good vacuum most of the molecules will remain neutral. You would have a mixture of H2O, HO, H, O, and some H2 and O2. You would do better with simply air. . Helium is a standard for plasma studies, and you can get some cheap from a party ballon. It is not excatly pure, but...

As far as flammable gas, it is not a problem in a vacuum (like ~ 1/10,000 of an atmosphere, because there is very little there. Venting of the vacuum pump and input concerns would have to be addressed.

As far as a flamable gas of any kind in a microwave- it is not a good idea. It will burn, and if the air/ fuel mixture reaches the right proportions, it will explode with any spark. Creating a plasma in a Microwave is a common 'experiment'. Smoke from a burned match, or even a grape works well. Be aware though that microwave ovens can be damaged, especially if run for more than a few seconds.

As for the magnet drawing. I don't know the purpose of the coiling. The solid tubes (with electromagnets inside would magnetically shield the grid. Such ideas have been discussed before by Fusor hobbyists. It might increase the passes of ions or electrons before loss, but there is absolutely no way you could compress a plasma. The holes are too big, and the fields are not opposing. It is like trying to pump air in tire that has a lot of huge holes in it. Even with an extremely strong pump, the pressure would be minimal.
You can arrange magnets like in the Polywell, but the arrangement in the linked picture does not work for any presurizing or Wiffleball like effect.

Dan Tibbets
To error is human... and I'm very human.

Endersworld
Posts: 19
Joined: Sun Jan 22, 2012 10:25 am

Postby Endersworld » Mon Jan 30, 2012 4:44 am

Yeah, I just considered that. Im not sure how the microwaves treat a plasma generated from a electrical arc compared to a combustion process.

I welded the gas injector to the chamber to prevent unintentional arcing between the nozzle and the box.

I just finished a test circuit of the magnetron, using only the necessary components: http://i44.tinypic.com/1zxl7aa.jpg

You just plug it in and its on, I plan on adding a switch. I tested it with the microwave output aimed at a jar of water, and after a 20 second run it had heated the water. The next step is to create the waveguides and plasma generation chamber.

The chamber will be a hollow steel sphere, around which there will be three rings of steel core electromagnets; one ring per dimension.
The microwaves and plasma enter at the bottom through a metal tube.

Here's a diagram of the anticipated field lines around the ring cores
http://i43.tinypic.com/k2idc6.jpg

When I microwaved the fuel gas flame, the plasma moved up into the container. When I attached earth magnets to the outside of the jar, the plasma globe pushed away from the magnets into the corner.

The fields formed by the ring cores should hold the plasma stable in the center of the metal sphere.

kcdodd
Posts: 722
Joined: Tue Jun 03, 2008 3:36 am
Location: Austin, TX

Postby kcdodd » Mon Jan 30, 2012 7:13 am

I have used the method I mentioned earlier with similar results as you have gotten with a flame. The arc will actually be much hotter then the flame giving more free electrons for the microwave to work with.

As to the magnetic fields, I still don't quite see it. It looks like your coils are basically toroidal, which won't have much field inside your sphere.
Carter

ladajo
Posts: 6184
Joined: Thu Sep 17, 2009 11:18 pm
Location: North East Coast

Postby ladajo » Mon Jan 30, 2012 2:26 pm

I agree with Carter on your fields. I do not think they will manifest like you think they will.

What kind of run times are you looking for?
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)
What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

Endersworld
Posts: 19
Joined: Sun Jan 22, 2012 10:25 am

Postby Endersworld » Sun Feb 05, 2012 8:12 pm

It should run indefinitely, at least the lifetime of the magnetron. I attempted to repeat the plasma generation with the rebuilt magnetron circuit, but either the power level of that magnetron was too low, or the microwave distribution was incorrect. I pre-tested it on a jar of water, so it was working. the microwave i used to make the plasma was 1500 watts, this one is only 1200.

heres what i did in the microwave(1500 watt)
http://i39.tinypic.com/2m84lfp.jpg

and heres what i did after i put the other one together (1200 watt)
http://i39.tinypic.com/20paulh.jpg

How large of a hole can i have that wont let microwaves through? I had to drill holes to oxidize the flame, 2 about 1/4 inch in diameter.

hanelyp
Posts: 2237
Joined: Fri Oct 26, 2007 8:50 pm

Postby hanelyp » Mon Feb 06, 2012 6:34 am

As a rule of thumb, a hole less than 1/2 wavelength circumference won't let through microwaves. Assuming a 2.7GHz microwave, circular holes less than ~1.75 cm across will pass little energy.

kcdodd
Posts: 722
Joined: Tue Jun 03, 2008 3:36 am
Location: Austin, TX

Postby kcdodd » Mon Feb 06, 2012 9:15 pm

how big is that tube?
Carter

Endersworld
Posts: 19
Joined: Sun Jan 22, 2012 10:25 am

Postby Endersworld » Sat Feb 11, 2012 12:22 am

about 1.5 inches diameter...

kcdodd
Posts: 722
Joined: Tue Jun 03, 2008 3:36 am
Location: Austin, TX

Postby kcdodd » Sat Feb 11, 2012 12:44 am

Take a look at this page, which has a summary of waveguides: http://www.rfcafe.com/references/electr ... eguide.htm

In particular a circular waveguide is given. Based off of 1.5 inches diameter and their numbers, the the cutoff frequency for that cylinder would be about 4.6GHz, which means a 2.45GHz wave is not supported.
Carter

Endersworld
Posts: 19
Joined: Sun Jan 22, 2012 10:25 am

Postby Endersworld » Sun Feb 12, 2012 4:17 am

Hmm, that explains why I was not getting any output from the end of the tube. I set a jar with a small amount of water on top of that tube to test for output and it didn't heat.
I tested it before i welded the tube to the RF gasket and it heated the water

The microwaves were not transferring through the tube. After running the magnetron through the tube with a flame in it , the magnetron would become to hot too touch. I read that if theres no load, the microwaves recycle into the magnetron.

Maybe if I did something like this

http://i42.tinypic.com/33mndp2.jpg

http://i41.tinypic.com/142spqt.jpg


A narrow tube welded to the RF gasket, then a cone off that, and attached to a large tube.

The magnetron output sticks out a bit from the small tube, so it begins propagation in the cone, rather than than in the narrow tube, the narrow tube is just how its connected to the magnetron.

The tube after the cone would be 5 to 6 inches, with a thickness of half centimeter.

Endersworld
Posts: 19
Joined: Sun Jan 22, 2012 10:25 am

Postby Endersworld » Sat Apr 07, 2012 6:53 am

so...

I removed the fuel injector nozzle, and put in a arc gap.
its powered by a high voltage transformer and makes a good plasma on its own. I power on the transformer, establish an arc, and turn on the microwave.

It created very consistent bursts of plasma.

i only tested with copper electrodes, but I will be using tungsten, for lower degradation rate.


Return to “Design”

Who is online

Users browsing this forum: No registered users and 2 guests