Is There Anything In Physics That Prevents Engineering Uber Permanent Magnets?

[TomKerbal]

On 12/9/2022 at 5:16 PM, Beamer said:

The highest known remanent magnetization (basically, the magnetic strength of a material once it's outside of any external magnetic field) is around 1.3 Tesla for a neodynium-iron-boron magnet. Materials have a magnetic saturation level, the highest saturation levels are just over 2 Tesla, but to reach this value it actually has to be inside a stronger magnetic field (typically the core of an electromagnet). Although advances in material science might increase this a little further, it won't be huge jumps. So you can forget about 1 kT, or even 10 Tesla for that matter.

Note that a 1000 Tesla field will damage organisms and outright destroy electric circuitry, so the usefulness of magnetic fields of such magnitude tends to be limited to academic study. The highest practically useful magnetic fields go up to about 7 Tesla max in an MRI scanner, and up to 7.7 Tesla in the LHC. And you have to be very careful not to carry anything made of metal near those.

The highest 'permanent' magnetic field created with electromagnets is around 100 Tesla (which is enough to create horrible shrieking sounds whenever it is turned on). These can run for only a very short duration, a few seconds at best. Higher magnitudes have been reached but only by using shaped explosives or similar destructive methods (like laser compression or magnetic compression), so these are very short lived by their very nature. This sort of thing is mostly used in fusion reactor research.

 

Yes neodymium magnets (NdFeB) are really strong. I once saw a big screwdriver hovering (nearly) horizontally in front of a vertical mounted big neodymium magnet. I mean perpendicular to the surface. Very impressive to watch.

By the way these magnets are "magnetically hard" materials, so its remanence flux density does not change significant in external magnetic fields. But they are weak considering thermal stability due to its low Curie temperatures. Place them in an oven with 300 degC (what's that in Fahrenheits ? ;-) and they are good as babies :-)

I would admit that you can not build materials with much higher remanence flux densities. Stronger fields require high electric currents (generated by superconductors without Ohmic losses).

 

Have a great day, Tom

 

[Nuke]

On 12/11/2022 at 3:53 PM, K^2 said:

It loses mass to Hawking radiation constantly, and if starved will become rather violent at it, growing in brightness until it eventually explodes rather spectacularly, but even on the lighter side, that takes years. And if you go with a heavier black hole, utilizing Penrose process to get thrust rather than direct Hawking radiation pressure, we can be talking about a shelf life measured in millennia.

This absolutely isn't something you use for a shuttle, though. This is an interstellar liner designed to link up with a cycler somewhere in the outer system and head out to another star on a decades long voyage.

how does one couple their ship to the thing (without giving it an early snack of course)?

Edited January 5, 2023 by Nuke

[K^2]

4 hours ago, Nuke said:

how does one couple their ship to the thing (without giving it an early snack of course)?

By charging the black hole slightly. Ordinary matter couples to electromagnetic fields many orders of magnitude more strongly than to gravitational, so you can literally use a magnet to push against a Kerr-Newmann black hole without any worry about gravitational effects.

Thought, to be fair, I haven't ran the numbers on the actual magnetic field strength and the size of the magnet. I'll see if I can put some numbers to this tomorrow. Off the top of my head, all I can say is that this is easier with a larger black hole, which is what we're aiming for with a more sophisticated approach.