# What is the strongest practical magnet?

I thought that magnets stronger than a few telsa tear apart. What is the strongest practical magnet that could be used for something like a particle accelerator? I am asking for a theoretical or physical limit.

• Next LHC upgrade is hoping for 16T home.cern/about/updates/2018/06/… – Martin Beckett Oct 18 '18 at 2:23
• At Los Alamos a 100T magnet was recently tested. – nodarkside Oct 18 '18 at 3:02
• @nodarkside but that was a pulsed magnetic field. I think VINIEF reached $20\ \rm MG$ or so – user191954 Oct 18 '18 at 3:59

The strongest practical fields (used to do measurements) are pulsed fields, achieved by explosions, where also the samples are destroyed. It just lasts long enough to get a few oscillations of the deHaas-vanAlphen effect for example.

Explosives are used to squeeze a current loop, the "flux compression" method. Fowler et al. did such experiments in the desert around Los Alamos, achieving 100 tesla. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.68.534

For continuous fields, there is for example the diamagnetically levitating frog in 16 tesla: https://www.ru.nl/hfml/research/levitation/diamagnetic/

There isn't a theoretical limit for how strong a magnetic field can be: you can keep increasing the electric current and you should get a stronger field. Magnetars' fields can reach $$10^{15}\ \rm G$$. CERN (1, 2) is trying to put together stronger magnets for future accelerators.

But at higher magnetic field strengths, certain otherwise-negligible effects become more pronounced: since atoms contain both positive and negatively charged components, an atom moving in a magnetic field may experience a change in ionisation energy because the magnetic forces which act differently upon different components of the atom overwhelm the Coulomb attractive force.

So there's no theoretical limit on the strength of a magnetic field, but for particle accelerators, the maximum field usable depends on the design: if you can use a pulsed field, higher strengths are possible (Los Alamos has created $$1\ \rm MG$$ fields), but continuous fields are usually destructive beyond $$500\ \rm kG$$ (the exact value of the field which significantly distorts the atom is dependent upon the atomic number and other factors, and is discussed in the paper about ionisation energies I linked earlier).

• Magnetars are not practical to use because they would destroy anything around them. If there is a limit to tensile strength then it would probably limit magnets to a few thousand tesla or much less. – user33800 Oct 18 '18 at 4:55
• @user33800 um... magnetars are a kind of neutron star. I don't think there's ever been any attempt to use them in particle accelerators and there probably never will be: the smallest problem with trying to use them is probably the 20 kilometer diameter. I mentioned magnetars only as an example of a situation where really strong magnetic fields exist. – user191954 Oct 18 '18 at 4:57
• @user33800 I didn't claim that there's no theoretical limit for magnet strengths in particle accelerators. I said that there's no theoretical maximum magnetic field, but the last paragraph is about the maximum field strength for particle accelerators. There's no fixed, solid number that I could find, but there is definitely a limit and I discussed that briefly. – user191954 Oct 18 '18 at 5:14
• Ok well I accept the answer. – user33800 Oct 18 '18 at 5:14
• Note that a saturated rare-earth permanent magnet has a fiesurface field of about one tesla = 10 kG. – rob Oct 18 '18 at 5:23