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

[Spacescifi]

By uber I literally mean 1000 tesla strength permanent magnets and beyond.

 

Why?

 

I was thinking if such could be built you could configure them into a magnetic nozzle that would not need any power input for it's magnetic field.

 

Unless you are going to tell me that permanent magnets lose magnetism overtime... right?

[kerbiloid]

Covered with stuck wrenches and screwdrivers.

And a ten of skeletons in spacesuits.

[Beamer]

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.

 

[kerbiloid]

Spoiler

 

 

[Beamer]

2 hours ago, kerbiloid said:

  Hide contents

 

 

Didn't like the film, but I liked that scene, except it went bad again at the end when, despite being in a magnetic field strong enough to spaghettify her, she somehow manages to 'materialize' a circular saw and spin it up. Imagine the currents in that thing when it starts to spin. Spinning metal in a multi-Tesla magnetic field, bad idea terminator!

When I was in Uni in the early 90s I had a side job cleaning some of the University buildings to pay for my tuition. I had to clean some interesting buildings, forensic DNA labs, physics labs full of those tables with intricate laser/lens/mirror setups, frosted oxygen flasks steaming in room temperature, Silicon Graphics workstations around every corner, a veritable wonderland for a science and computer nerd like me. It included some labs with high powered electromagnets. Of course they had to be turned off when the people left the lab, but the huge array of warning labels on the door always made me a little nervous. The rules stated you always had to leave keys, wallets and any other metal or magnetized objects outside all the same, just in case someone forgot to flick a switch when they left

 

[K^2]

19 hours ago, Spacescifi said:

Why?

Every magnet wants to tear itself apart. The effective pressure of 1000T field is about 400GPa. Theoretical ultimate tensile strength of graphene, the toughest material we know, might be as high as 130GPa.

But there are, typically, significantly lower limits that come from statistical mechanics. Magnetism is always related to structure of the material, so it is a factor in phase transitions. Whether a phase is stable depends on whether it is an energy local minimum under given conditions. As in above, stronger field, means higher energy of that state. The best permanent magnets we've learned to make are superconductors. The highest critical field for the best ones we know at pretty much absolute zero are just under 30T. So that's the limit for what we've found. You might be able to go a little higher than that, but not by a lot, as the energy grows as the square of the field intensity.

[KSK]

18 hours ago, Beamer said:

Didn't like the film, but I liked that scene, except it went bad again at the end when, despite being in a magnetic field strong enough to spaghettify her, she somehow manages to 'materialize' a circular saw and spin it up. Imagine the currents in that thing when it starts to spin. Spinning metal in a multi-Tesla magnetic field, bad idea terminator!

When I was in Uni in the early 90s I had a side job cleaning some of the University buildings to pay for my tuition. I had to clean some interesting buildings, forensic DNA labs, physics labs full of those tables with intricate laser/lens/mirror setups, frosted oxygen flasks steaming in room temperature, Silicon Graphics workstations around every corner, a veritable wonderland for a science and computer nerd like me. It included some labs with high powered electromagnets. Of course they had to be turned off when the people left the lab, but the huge array of warning labels on the door always made me a little nervous. The rules stated you always had to leave keys, wallets and any other metal or magnetized objects outside all the same, just in case someone forgot to flick a switch when they left

 

Yeah, bank cards and NMR magnets don't mix well. Ask me how I know.

Back to the original question - there are limits on how strong a permanent magnet can be, which are down to both it's chemical structure and crystal microstructure.

As a very loose analogy, picture a row of ordinary bar magnets lined up with all their poles aligned:

 N  N  N  N  N  N  N  N 
 [] [] [] [] [] [] [] []
  S  S  S  S  S  S  S  S

Please excuse the bad ASCII art, but I think you can see what's going to happen here. Given half a chance, those magnets are going to rearrange themselves to:

 N  S  N  S  N  S  N  S 
 [] [] [] [] [] [] [] []
  S  N  S  N  S  N  S  N

Unless there's some other factor constraining them. For a row of two or three bar magnets, that's not too tough, but the more magnets in the row, the harder it is to keep them all pointing in the same direction - which is what you want for the biggest overall magnetic field. As K^2 said, every magnet wants to tear itself apart.

Edited December 10, 2022 by KSK

[kerbiloid]

The engine should throw back the permagnets pushed out by the next permagnet in queue.

Thus, no nozzle is needed only a pipe.

[StrandedonEarth]

Monopoles would make this much easier

[kerbiloid]

Prohibited by the antimonopoly laws.

[sevenperforce]

On 12/8/2022 at 9:24 PM, Spacescifi said:

I was thinking if such could be built you could configure them into a magnetic nozzle that would not need any power input for it's magnetic field.

Even apart from all of the reasons why you can't have 1000 Tesla permanent magnets, what you're trying to do wouldn't even work to start with.

Earnshaw's theorem says that you can't have a stable arrangement of fixed magnets, electrostatic charges, or other electromagnetic field interactions which results in a constant force being applied to something without destabilizing torque. 

So even if you did have super-powerful permanent magnets, they would not allow you to push charged particles out the back of your vehicle without an input of power.

[kerbiloid]

A solid fuel permagnetic booster.

Just take enough of steel balls, or pour a magnetic liquid like blood.

Spoiler

 

Make the pusher ball electromagnetic to switch it off after shot and return it to the start position with a rubber band.

***

Offtopic, but too amusing to skip.

Spoiler

 

[Spacescifi]

6 hours ago, sevenperforce said:

Even apart from all of the reasons why you can't have 1000 Tesla permanent magnets, what you're trying to do wouldn't even work to start with.

Earnshaw's theorem says that you can't have a stable arrangement of fixed magnets, electrostatic charges, or other electromagnetic field interactions which results in a constant force being applied to something without destabilizing torque. 

So even if you did have super-powerful permanent magnets, they would not allow you to push charged particles out the back of your vehicle without an input of power.

 

Has anyone put Earshaws theorem to the test or has it been proven at both macro and micro scaling (I am aware tiny things do not behave exactly like normal or bigger things)?

Edited December 11, 2022 by Spacescifi

[RandomGrape]

What is a uber magnet, why am I here?

[kerbiloid]

45 minutes ago, RandomGrape said:

What is a uber magnet, why am I here?

Spoiler

"Magnet"
"Uber"

Uber next to Magnet.

 

Edited December 11, 2022 by kerbiloid

[sevenperforce]

6 hours ago, Spacescifi said:

Has anyone put Earshaws theorem to the test or has it been proven at both macro and micro scaling (I am aware tiny things do not behave exactly like normal or bigger things)?

Yes, Earshaw's theorem has been fully and completely tested, not only empirically but mathematically.

Most things in physics cannot be "proven" per se, but there are exceptions. Certain physical systems can be modeled mathematically and can have mathematical proofs applied to them.

Earshaw's theorem is every bit as proven as the fact that pi is an irrational number.

[kerbiloid]

14 minutes ago, sevenperforce said:

Most things in physics cannot be "proven" per se, but there are exceptions.

All things in physics can only be unproven or stay uncertain.

[K^2]

16 hours ago, sevenperforce said:

Even apart from all of the reasons why you can't have 1000 Tesla permanent magnets, what you're trying to do wouldn't even work to start with.

Earnshaw's theorem says that you can't have a stable arrangement of fixed magnets, electrostatic charges, or other electromagnetic field interactions which results in a constant force being applied to something without destabilizing torque. 

So even if you did have super-powerful permanent magnets, they would not allow you to push charged particles out the back of your vehicle without an input of power.

Well, ok, this is definitely getting into the territory of "Theoretical s*** that won't happen for 500," but Earnshaw's theorem applies to static equilibrium, not dynamic equilibrium. That's why type II superconductor magnetic levitation via quantum flux locking exists. (I hate that "quantum levitation" made its way into the literature. Any magnet is quantum. Should I call my HDD a quantum storage device? Ugh. /rant)

In theory, and I mean this in the loosest way possible that's still compatible with underlying mathematics of the known physics, if you could arrange for a superconducting, superfluid current sitting inside a superconducting magnetic "bottle" that self-balances with a prominently extended finger to Earnshaw it could maintain an immense pressure. Setting aside the question of how that "bottle" doesn't crack under that pressure, you can absolutely manipulate the "opening" of it to generate a jet stream out the back, that's going to be 100% efficient conversion of the electromagnetic pressure inside the bottle into the exhaust kinetic energy, thanks to the whole thing requiring superfluidity in the first place. Lasing matter is all the rage, apparently.

The thing that makes this not a blatant violation of all things holly (Noether's Theorem) is that your magnet in this case isn't working as a drive. No work is done by the magnetic field. It's just there to give you a way to maintain a pressure you couldn't by any other means. Other than that, it's just a water bottle rocket. Just, you know, at terapascals of pressure. Again, don't ask me how the "bottle" survives this or how you load it. And we also don't have the materials with the sufficient critical fields, let alone these which exhibit both superfluidity and superconductivity at the same time, and anything else would turn that energy into heat, instantly turning the entire vessel into a rapidly expanding cloud of plasma. Which is the wrong kind of propulsion.

There is some theoretical work suggesting that metallic hydrogen under the right conditions becomes a superconducting supersolid, and supersolids are superfluid enough for the purposes of this discussion. But we're talking, you know pressure of a gas giant interior at pretty much absolute zero? Optimistically? Which, good luck. And I don't mean good luck to us, because , but to any super-advanced civilization anywhere ever.

Just to put that into a perspective, I think we're better off working on a black hole drive. I don't know where we'll get a black hole in low kiloton ranges, but I can at least picture how we'd use one to push a starship if we managed to find/make one.

[Spacescifi]

34 minutes ago, K^2 said:

Well, ok, this is definitely getting into the territory of "Theoretical s*** that won't happen for 500," but Earnshaw's theorem applies to static equilibrium, not dynamic equilibrium. That's why type II superconductor magnetic levitation via quantum flux locking exists. (I hate that "quantum levitation" made its way into the literature. Any magnet is quantum. Should I call my HDD a quantum storage device? Ugh. /rant)

In theory, and I mean this in the loosest way possible that's still compatible with underlying mathematics of the known physics, if you could arrange for a superconducting, superfluid current sitting inside a superconducting magnetic "bottle" that self-balances with a prominently extended finger to Earnshaw it could maintain an immense pressure. Setting aside the question of how that "bottle" doesn't crack under that pressure, you can absolutely manipulate the "opening" of it to generate a jet stream out the back, that's going to be 100% efficient conversion of the electromagnetic pressure inside the bottle into the exhaust kinetic energy, thanks to the whole thing requiring superfluidity in the first place. Lasing matter is all the rage, apparently.

The thing that makes this not a blatant violation of all things holly (Noether's Theorem) is that your magnet in this case isn't working as a drive. No work is done by the magnetic field. It's just there to give you a way to maintain a pressure you couldn't by any other means. Other than that, it's just a water bottle rocket. Just, you know, at terapascals of pressure. Again, don't ask me how the "bottle" survives this or how you load it. And we also don't have the materials with the sufficient critical fields, let alone these which exhibit both superfluidity and superconductivity at the same time, and anything else would turn that energy into heat, instantly turning the entire vessel into a rapidly expanding cloud of plasma. Which is the wrong kind of propulsion.

There is some theoretical work suggesting that metallic hydrogen under the right conditions becomes a superconducting supersolid, and supersolids are superfluid enough for the purposes of this discussion. But we're talking, you know pressure of a gas giant interior at pretty much absolute zero? Optimistically? Which, good luck. And I don't mean good luck to us, because , but to any super-advanced civilization anywhere ever.

Just to put that into a perspective, I think we're better off working on a black hole drive. I don't know where we'll get a black hole in low kiloton ranges, but I can at least picture how we'd use one to push a starship if we managed to find/make one.

 

Ah I see... danger Will Robinson! We are talking liquid explodium creating uber magnetic fields, you crash this thing and it is not blowing up small... it's going off like a nuke.

Still thanks for indulging the science of this Brain.

 

Regading black hole rocketry, what happens when you are not feeding it with propellant? You cannot just shut it off right?

Why would a black hole starship not melt itself from the blackbod radiation of the black hole?

[K^2]

29 minutes ago, Spacescifi said:

Regading black hole rocketry, what happens when you are not feeding it with propellant? You cannot just shut it off right?

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.

[sevenperforce]

3 hours ago, K^2 said:

if you could arrange for a superconducting, superfluid current sitting inside a superconducting magnetic "bottle" that self-balances with a prominently extended finger to Earnshaw it could maintain an immense pressure.

True, but then you'd need an energy source from somewhere else to accelerate the propellant, instead of using a magnetic nozzle to do it (which I believe was the original plan).

2 hours ago, Spacescifi said:

We are talking liquid explodium creating uber magnetic fields, you crash this thing and it is not blowing up small... it's going off like a nuke.

More importantly, all your "uber" magnetic fields still won't accelerate your propellant. You'll need a source of energy to do that, just as you would if you didn't have a magnetic nozzle.

[K^2]

3 hours ago, sevenperforce said:

True, but then you'd need an energy source from somewhere else to accelerate the propellant, instead of using a magnetic nozzle to do it (which I believe was the original plan).

The energy would be of the magnetic field inside. The way I'm picturing this, the containment vessel would not be magnetized, but rather simply be a superconductor, so it will gain magnetization via Meissner effect in response to the magnetic field of the propellant. The propellant's field would then be tied directly to its circulation, so as it's being expelled out the back by its own magnetic pressure, the field inside is going to be dropping, reducing the contained energy. Again, just like a water bottle, but instead of a compressed air being a working fluid, the working "fluid" is the magnetic field itself.

The energy can be quite significant. 30T is 360MJ/m³. Which isn't fantastic in terms of per-volume energy density, but it all depends on how light the containment could be. And again, because this scales as a square of the field strength, you "only" need to get to 300T to be beating Jet-A, which is 35GJ/m³. Of course, even if you had a superconductor that can take 300T, there is no way your containment is going to be lighter than 820kg of Jet-A in an aluminum drum. 

This is similar to the problem of storing energy for a rocket in a flywheel. Which sounds ridiculous, until you think about it, and then you think why aren't we doing it, until you do the math. If you take a light spool and wind very strong cable around it, then spin up the cable until it's moving at a few km/s, and release the free end, with the right choice of material properties, and maybe a bit of electromagnetic guiding, you can make sure that the cable releases at a fixed angle, providing consistent thrust to the rocket. And, well, the I_SP is however fast the cable's moving divided by g₀. In principle, this could be as high as you want. In practice, centrifugal force will try to rip the cable apart. A kevlar cable will fail at 470m/s. (Still, getting 50s I_SP out of a flywheel with a cable is probably more than what people expect.) So the limit of this purely mechanical setup is till the strength of the chemical bonds, just like in the conventional chemical rocket case.

It is perhaps a surprising, but actually quite natural result in physics that whenever you're looking at a way of storing energy, at some scale, that's going to involve forces that are going to be at least in the ballpark of what you'd get if you were to picture this as a compressed spring or an ideal gas. That's why nuclear energy is so much more potent. Much harder to split the atom than any chemical bond. So just about anything else we come up with will be worse.

[Dinlink]

On 12/9/2022 at 3:24 AM, Spacescifi said:

By uber I literally mean 1000 tesla strength permanent magnets and beyond.

 

Why?

 

I was thinking if such could be built you could configure them into a magnetic nozzle that would not need any power input for it's magnetic field.

 

Unless you are going to tell me that permanent magnets lose magnetism overtime... right?

There is your natural ocurring "Uber permanent magnet":

https://en.m.wikipedia.org/wiki/Magnetar

It can get between 1 and 100 billion Teslas...

So.. I think physics doesn't forbids it ... Just that it could be a little inconvenient to use as a rocket nozzle...

 

 

[Snark]

Out of curiosity, I tried putting the OP question verbatim (subject line + question) into the AI bot ChatGPT,  and the answer it gave was surprisingly coherent and on point. 

Quote

There is no fundamental law of physics that prevents the creation of permanent magnets with extremely high magnetic field strengths, such as 1000 tesla or beyond. However, there are several practical challenges that make it difficult to create and use such magnets in engineering applications.

One of the main challenges is that the materials that are commonly used to create permanent magnets, such as iron, cobalt, and neodymium, become physically unstable at very high magnetic field strengths. This means that the magnets would likely break or shatter if they were subjected to such high fields.

Another challenge is that the magnetic field of a permanent magnet decreases with distance. This means that in order to create a magnetic nozzle with a sufficiently strong field, the magnet would have to be placed very close to the nozzle, which could be difficult to achieve in practice.

Finally, the cost and difficulty of creating and maintaining such high-strength magnets would likely make them impractical for most engineering applications.

Overall, while it is theoretically possible to create permanent magnets with extremely high magnetic field strengths, there are several practical challenges that make it difficult to do so in practice.

 

[kerbiloid]

https://en.wikipedia.org/wiki/SCIgen