dorsal/arxiv
View SchemaSuperconducting pipes and levitating magnets
| Authors | Yan Levin, Felipe B. Rizzato |
|---|---|
| Categories | |
| ArXiv ID | physics/0609141 |
| URL | https://arxiv.org/abs/physics/0609141 |
| DOI | 10.1103/PhysRevE.74.066605 |
Abstract
Motivated by a beautiful demonstration of the Faraday's and Lenz's law in which a small neodymium magnet falls slowly through a conducting non-ferromagnetic tube, we consider the dynamics of a magnet falling through a superconducting pipe. Unlike the case of normal conducting pipes, in which the magnet quickly reaches the terminal velocity, inside a superconducting tube the magnet falls freely. On the other hand, to enter the pipe the magnet must overcome a large electromagnetic energy barrier. For sufficiently strong magnets, the barrier is so large that the magnet will not be able to penetrate it and will be suspended over the front edge. We calculate the work that must done to force the magnet to enter a superconducting tube. The calculations show that superconducting pipes are very efficient at screening magnetic fields. For example, the magnetic field of a dipole at the center of a short pipe of radius $a$ and length $L \approx a$ decays, in the axial direction, with a characteristic length $\xi \approx 0.26 a$. The efficient screening of the magnetic field might be useful for shielding highly sensitive superconducting quantum interference devices, SQUIDs. Finally, the motion of the magnet through a superconducting pipe is compared and contrasted to the flow of ions through a trans-membrane channel.
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"abstract": "Motivated by a beautiful demonstration of the Faraday\u0027s and Lenz\u0027s law in\nwhich a small neodymium magnet falls slowly through a conducting\nnon-ferromagnetic tube, we consider the dynamics of a magnet falling through a\nsuperconducting pipe. Unlike the case of normal conducting pipes, in which the\nmagnet quickly reaches the terminal velocity, inside a superconducting tube the\nmagnet falls freely. On the other hand, to enter the pipe the magnet must\novercome a large electromagnetic energy barrier. For sufficiently strong\nmagnets, the barrier is so large that the magnet will not be able to penetrate\nit and will be suspended over the front edge. We calculate the work that must\ndone to force the magnet to enter a superconducting tube. The calculations show\nthat superconducting pipes are very efficient at screening magnetic fields. For\nexample, the magnetic field of a dipole at the center of a short pipe of radius\n$a$ and length $L \\approx a$ decays, in the axial direction, with a\ncharacteristic length $\\xi \\approx 0.26 a$. The efficient screening of the\nmagnetic field might be useful for shielding highly sensitive superconducting\nquantum interference devices, SQUIDs. Finally, the motion of the magnet through\na superconducting pipe is compared and contrasted to the flow of ions through a\ntrans-membrane channel.",
"arxiv_id": "physics/0609141",
"authors": [
"Yan Levin",
"Felipe B. Rizzato"
],
"categories": [
"physics.class-ph",
"cond-mat.supr-con",
"physics.gen-ph"
],
"doi": "10.1103/PhysRevE.74.066605",
"title": "Superconducting pipes and levitating magnets",
"url": "https://arxiv.org/abs/physics/0609141"
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