Magnetic Monopole?

[fechter]

A thought came to mind as I was working with some magnets the other day. What if you took a bunch of slightly curved magnet pieces and tiled them together into a hollow sphere? If the pieces were shaped like the sections on a soccer ball and each piece was magnetized such that the outside was, say, north and the inside was south, you could tile them together into a hollow sphere that was all north on the outside.

I know from experience that when tiling magnets, the sections will strongly repel each other and require a bit of force to hold them in place, but once glued or clamped, they behave like a single larger magnet.

So what would happen if you attempted to make a sphere from these pieces? Would the south flux inside leak through the cracks? If the pieces were well fitted and tightly glued together, I don't think the presence of the joints between pieces would be significant or they could be tongue and groove to make it more homogenous. Would the flux choke off to zero once the last tile was placed? If there was one small opening in the sphere, would all the south flux be concentrated into the opening and become super strong?

If you had a pair of "north" balls, they could alway repel each other, regardless of orientation.

I don't know of any practical application for such a thing either, just more of a theoretical exercise.

 

[flathill]

They are called magic spheres and were invented shortly after the halbach array

Really

 

[Kingfish]

Yes, exactly. There was a Halback Sphere as I recall. Found the link

Wickedly strong field strength! KF

 

[Drunkskunk]

I wounder what that would do to anything in the center of the sphere?

 

[fechter]

Interesting. Thanks for the Wiki link.

I've messed with a 3T MRI coil. Keep the steel oxygen cylinders far away! A very high flux density can do some interesting things. With enough, you can levitate a chunk of carbon motor brush.

OK, well I guess somebody already tried that, though I still don't have a good answer to some of my questions.

 

[amberwolf]

magnetic bearings--use all north races and balls, or all south?

 

[Kingfish]

The primary purpose of strong magnetic fields shaped in this manner is for fusion containment. Some years ago… no, make that ½ a lifetime ago, I worked directly across the street from the largest magnetic production facility on the planet: The MFTF-B at LLNL. This exotic machine cost a ¼ Billion to make, and once it was completed in 1985, they fired it up to prove it could work (and it did), then they shut it down and mothballed it cos the Tokomak was more successful politically and won the funding.

Another name for the MFTF-B was Magnetic Mirror Fusion. There was an odd-shaped Yin-Yang magnet at the heart of it: I used to wonder over to the building at lunchtime and walk about the structure. One day that had the insides opened up to where you could look in and see: Layers upon layers of fancy machining and exotic metal, and yet it was very alien. I couldn’t wait for it to start producing results, but it was all for naught: LLNL moved on with other technologies using lasers, and the MFTF-B was slowly torn down and scrapped.

Magnetic bottles though are still important for capturing antimatter as well as holding plasma, the power of the sun. One day I hope we’ll be able to master this art and use it for more than tapping into simple fusion, but also for space travel between planets and stars. Wouldn’t that be fun! 8)

Halbach was an interesting man, and he had a penchant for experimenting with conservation of momentum, and created magnetic drives bound in vacuum. I think the idea was if a machine could store momentum into a frictionless device (such as a Halbach Sphere or cylinder in vacuum) it would revolutionize energy storage. I believe these were his last persuits.

Reminiscing, KF

 

[flathill]

http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA311457

Magic spheres and torus us

 

[flathill]

The primary purpose of strong magnetic fields shaped in this manner

Halbach was an interesting man, and he had a penchant for experimenting with conservation of momentum, and created magnetic drives bound in vacuum. I think the idea was if a machine could store momentum into a frictionless device (such as a Halbach Sphere or cylinder in vacuum) it would revolutionize energy storage. I believe these were his last persuits.

Reminiscing, KF

http://en.wikipedia.org/wiki/Superconducting_magnetic_energy_storage
Zero friction to magnetic flow and friction helium 3 and space plasma forma helix us

 

[dkw12002]

As you know, the high speed trains run by Maglev, so magnetic forces can be spectacular. What I think might work is a maglev generator where you could turn the generator using bike pedals which would turn more easily than other generators with the turbine blades floating on air and thus recharge your electric motor which then runs the bike. It would be regenerative charging that is much more efficient. Of course if it works, then you wouldn't even need batteries. The best toy McDonalds every put out was a Hello Kitty top. The top was suspended in air by like magnetic poles with only a frame to keep the top in place. You could give it a spin and it would keep spinning for several minutes.

At Disney World there is this huge round marble ball weighing several tons, but resting on a film of water so you can spin it with your hands. It dawned on me, that the forces behind a spinning ball of that size should be able to run a generator for a few seconds if the entire weight of the ball were transferred to a generator, especially if what turned the ball was not hands, but a maglev circular electromagnetic housing corresponding to magnets placed in the ball in close proximity. Now when you get that water ball eventually spinning a couple thousand rpms, which might take you an hour or so, you can generate some net electricity by allowing the spinning ball to turn a generator. The net gain would come from magnetic forces.

 

[liveforphysics]

You will actually find bearing losses are extremely low in a generator of any type. Under 1% for most things.

Going to magnetic bearings only has the potential to reduce this 1% loss to something like 0.05% or so, because magnetic bearings suffer from eddy current losses.


Power in is not going to exceed power out. You can just try to minimize the amount of loss you have in the conversion process of power in to power out. In this case, reducing the bearing friction is a fairly insignificant area to focus on reducing loss, but the percent or so saved could perhaps be worth the effort in massive scale systems were a single percent can be hundreds of kW's, or even a MW.

 

[Jozzer]

On the other hand, 1% might be more than 1/4 of the losses in an otherwise efficient motor..

 

[fechter]

One of the articles I ran across talked about using a Halbach array to create a strong, uniform magnetic field across a rather large rotor area. In a motor or generator, the 'gap' could be very large as the field was uniform everywhere inside the gap. This would allow much more copper/reinforcement in a coreless build.

 

[Kingfish]

If the size (1x1xL) and shape (rect) and pole-orientation (thru side) were uniform, and that same one magnetic design repeated over again, then the cost would be the least – except that you’d need twice the magnets (implied). Radial Flux would work pretty well for this, though Axial Flux – less so because of the ever-increasing gap. Indeed, large rotors would benefit!

From my studies, 5-8mm thickness is optimum from both price and field strength. If you wanted to replicate the 9C hub with the 23 pole-pairs as a guide, then the mean diameter of the rotor would play out as:

• C = πd, C = width of 23 pole-pairs = 23 * (4 magnet sides * width of magnet)
  Rewritten: d = C/π = (23 * 4w)/π
  If w = 5mm, d = (23 * 4 * 5)/π = 460/π = 146.4mm
  If w = 8mm, d = 736/π = 234.3mm

In comparison to the 9C rotor, the inside diameter is about 205mm, and the magnet thickness appears to be < 3mm. So creating a Radial Flux motor using – say 7mm wide magnets would lend approximately the same sized hub motor, though with substantially more potential torque.

Hmmm, this is looking interesting...
Time to make another pot of Joe, KF

 

[fechter]

To replace the stock magnets in a hub motor with a Halbach array, the magnets would need to be narrower to accomodate the sideways ones between the main poles. You'd still have an iron core and about the same gap, so I don't know if you would gain much. You wouldn't need the back iron, so if it was possible to remove the existing, you could save quite a bit of weight. I suspect some back iron will still help but you could use a much thinner piece without saturating.

In a coreless design, it looks like there could be much more benefit. A typical coreless motor uses magnets on one side and back iron on the other side, so the flux in the gap will diminish quickly as the gap increases. It appears a Halbach array will maintain a much higher flux over a large gap so more room for copper. The windings are the challenge on a coreless motor.
A large diameter axial arrangement could use nearly rectangular magnet pieces. It might be possible to leave the gaps open and just use off the shelf magnets. It might also work to make some iron wedges to fill the gaps. Grinding magnets is nearly impossible. I wonder if you can cut them with EDM?