My little home made air-core solenoid makes 1.5T, why is it that superconducting electromagnets often aren't stronger than one would expect. Take the japanese maglev train for example: http://www.supraconductivite.fr/en/index.php?p=applications-trains-maglev-more According to this article the magnets are superconducting and have 700,000 amps going through them. Let's assume they were to use only 250 turns per meter then B=u0(N)(I) which would already be 220 Teslas. But according to the article it's only 5 Teslas strong what am I missing here? Obviously you wouldn't want 220 Teslas because of the compressive forces but wouldn't you want more than 5? And if for design reason you only needed 5 then it really doesn't seem like you would need to be superconducting, 5 T can be achieved with only a few thousand amps. Also MRI machines are only 1.5T and they're superconducting as well. Please help clarify.