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4hv.org :: Forums :: General Science and Electronics
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Magnetic field question

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Turkey9
Sun Jun 01 2008, 05:19AM Print
Turkey9 Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
hello
Does anyone out there know if there is a way to create a magnetic field where the field lines travel in a circle consentric with the shape of the coil? Lets say that there is a washer-like ring, I am wondering if there is a way to get the magnetic field lines to flow in a circular path above the surface of the washer-like ring. At first when I thought about this I thought of a toroidal electromagnet, but after some research found that in that situation there is no magnetic field outside of the coil. Possibly many many small solenoids lined end to end in a circle with a gap between the cores, allowing the field to escape...

thanks!
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rp181
Sun Jun 01 2008, 01:44PM
rp181 Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
you could arrange several coils in a circular fashion vertically.
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Dr. Slack
Sun Jun 01 2008, 03:58PM
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
If the washer-like ring is lying on a horizontal surface, then a vertical wire carrying current through the centre of the ring will generate a magnetic field around the ring, above and below it. Of course there is no such thing as an isolated wire, so you need to choose whether to bring the current back down again in one place a long way away, or in a cylindrical shell outside the washer. Think of the way a toriodal transformer is wound.
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rp181
Sun Jun 01 2008, 04:14PM
rp181 Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
that will also require lots of power to get a significant field, why do you need this?
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Turkey9
Sun Jun 01 2008, 08:26PM
Turkey9 Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
It's for a science fair project. I'm working on redesigning an electric thruster called a Pulsed Inductive Thruster to allow for more efficient opperation. For the thruster to work there must be a propper orientation between magnetic and electric field lines.
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Dr. Slack
Mon Jun 02 2008, 09:22AM
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
You will only get circular field lines inside a toroidal solenoid. However, if the solenoid is wound quite sparsely, consisting of a few discrete coils as you appear to suggest, then you will get a reasonably uniform field inside, and little leakage field outside. The gaps will allow you to see inside, and give access for supports and wires and to poke the demonstration.

Perhaps you'd post a sketch of the sort of configuration you're after, then we can see whether you'd need to break the laws of physics or not (hint, somewhat easier if laws don't need to be broken)
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Turkey9
Mon Jun 02 2008, 06:30PM
Turkey9 Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
here's a sketch of what i want. the thruster is basically a very big induction launcher for plasma that runs from lorentz law.
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DrZoidberg
Mon Jun 02 2008, 06:36PM
DrZoidberg Registered Member #350 Joined: Mon Mar 27 2006, 05:14PM
Location:
Posts: 106
You forgot to attach the sketch.
As I understood it it's a coilgun that uses gas as a projectile instead of a metal object.
But I don't get why you need the field lines to go parallel to the surface of the ring.
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Turkey9
Mon Jun 02 2008, 09:02PM
Turkey9 Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
oops here it is...

the way the thruster works is that there is a flat coil that accelerates a plasma away from the surface. The orientaion between the magnetic field and electric field has to be around perpendicular for a force to be applied to the ions according to lorentz law. The orientation is correct if a flat spiral coil is used (like an induction launcher) but in the process of my redesigning the electic field direction needs to change, and thus the magnetic field. This is still just an idea and i'm trying to figure out if it's even possible. If it's not then i'll just have to improve on my other design.
1212440530 1451 FT46353 Coil
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Firefox
Mon Jun 02 2008, 09:34PM
Firefox Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
A toroidal coil would give you a magnetic field close to that. You could also get somewhat less close to that by arranging several (8+) pancake coils with holes in the center in a circle.
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