Pardon my ignorance, but YBCO is not very far below its critical temperature at 77K, and applying a current/magnetic field lowers the critical temperature– so doesn’t LN not allow a very high magnetic field to be run?
All the MRIs I’m aware of (even those using high temperature ceramic based superconductors) operate below 20K, generally using cryocoolers.
From what I’ve read, YBCO functions just fine at LN temps under so-called ‘self field’, EG, the magnetic field generated by a current flowing in a single filament. These conditions would occur for say, power transmission.
But because magnets are a winding, the field is much higher than the self field (adjacent wires fields overlap one another), thus lowering the amount of current that can be passed through without exceeding the critical conditions (current, field, temperature– effectively a measure of the latent energy available to the lattice).
For example, the levitation coil of MIT’s LDX experiment is composed of Bi-2223 with a critical temperature of 104K. At 77K (LN cooled) it can carry 28 amps, whereas the self-field critical current is 63 amps.
(from http://www.psfc.mit.edu/~radovinsky/papers/43.pdf).
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Pardon my ignorance, but YBCO is not very far below its critical temperature at 77K, and applying a current/magnetic field lowers the critical temperature– so doesn’t LN not allow a very high magnetic field to be run?
All the MRIs I’m aware of (even those using high temperature ceramic based superconductors) operate below 20K, generally using cryocoolers.
AFAIK, YBCO is designed to work with LN.
MRIs typically use Niobium-titanium, which requires liquid helium for cooling.
From what I’ve read, YBCO functions just fine at LN temps under so-called ‘self field’, EG, the magnetic field generated by a current flowing in a single filament. These conditions would occur for say, power transmission.
But because magnets are a winding, the field is much higher than the self field (adjacent wires fields overlap one another), thus lowering the amount of current that can be passed through without exceeding the critical conditions (current, field, temperature– effectively a measure of the latent energy available to the lattice).
For example, the levitation coil of MIT’s LDX experiment is composed of Bi-2223 with a critical temperature of 104K. At 77K (LN cooled) it can carry 28 amps, whereas the self-field critical current is 63 amps.
(from http://www.psfc.mit.edu/~radovinsky/papers/43.pdf).
Very interesting. I did not know that.