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I Superconductors and Wiring

  1. Oct 12, 2018 #1
    Zero resistance in wiring seems to be the technology in the future. Any resistance in the transmission wiring acts like loads so it's like the current wastes itself on the resistances in the wiring and heat that occurs. So lossless wiring seems to be the ultimate goal.

    In Large Hadron Collider, is the Superconductors in the wiring purpose is to transmit lossless power or is it mainly to get Meissner effect in influencing the particle paths?

    And what is the latest in High temperature superconductors.. have they figured out the secrets already? Does it involve new physics or just a 1 in million right combinations of alloys?

    What power systems in the world use superconductors for lossless transmission.. any in Japan?
    Lastly, does it mean zero resistance wires (can only superconductors do this?) never get hot from the current?
     
  2. jcsd
  3. Oct 12, 2018 #2
    It would seem you need a review on the current state of superconductivity. Maybe start here http://iopscience.iop.org/journal/0034-4885/page/Celebrating 100 years of superconductivity.

    The main reason people use superconductors for magnets is because supercondctors can sustain large current density. If you used normal wires to get large magnetic fields, you would get into a spiral of: wires are too hot -> lets increase wire cross-section -> now magnetic field is smaller because wires are too large -> repeat.

    High-Tc superconductors are not yet fully understood, but this is not the main problem. The main problem is that they are hard to make into wires, so using them in practice, e.g. for magnets, is expensive.

    Regarding getting hot. Superconductors are loss-less for DC currents. There they don't get hot. However if current is changing, even superconductors become (a little bit) lossy.
     
  4. Oct 12, 2018 #3

    ZapperZ

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    Please note, as alluded to by Cryo, that zero resistance is only in DC mode. Superconductors typically do not have zero AC resistance.

    I'm not sure why the Meissner effect would be relevant here. The particles are not going through the bulk material of the superconductor (which would be tragic if they are), which is where the Meissner effect occurs. So why would this effect influence the path of the particles?

    Why not? If you pass a large enough current through it, you can quench superconductivity and it will definitely gets hot. And as stated above, they certainly can get hot under AC current since the AC resistance is not zero.

    Zz.
     
  5. Oct 12, 2018 #4
    Oh.. I thought levitating trains used the Meissner effect.. and instead of levitating trains..they levitate particles in LHC. Reading this. http://supraconductivite.fr/en/index.php?p=applications-trains-maglev-more It's not so.


    Y8NJu0.jpg

    Can't trains or any locomotion use the above principles? https://en.wikipedia.org/wiki/Meissner_effect

    Does this have to do with impedance? So superconductors also have impedance? I thought the electrons became super, and like superman.. can violate ordinary laws of physics.
     
  6. Oct 12, 2018 #5

    ZapperZ

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    But what does that have anything to do with directing the direction of the particles?

    I can levitate trains using ORDINARY magnets! I do not need superconducting magnets, in principle. For many practical reason, I'd like to use superconducting magnets because I can use less current to create the same magnitude of magnetic field, AND, I have the added advantage of using Type II superconductors and flux penetration for mechanical stability.

    But this has nothing to do with guiding the particles. So, to address your point, the Meissner effect has no bearing on guiding particles. I worked at a particle accelerator and we used ordinary electromagnets to guide these particles.

    I have no idea what you mean by "impedence" here. You have impedence even with zero resistance, depending on whether you have capacitors and/or inductors in the circuit.

    But you seem to ignore what you've been told regarding DC and AC resistance. Maybe you do not understand why there is a non-zero AC resistance?

    Zz.
     
  7. Oct 12, 2018 #6
    Skin effect?
    https://en.m.wikipedia.org/wiki/Skin_effect
     
  8. Oct 12, 2018 #7

    ZapperZ

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  9. Oct 12, 2018 #8
    I googled "non-zero AC resistance" and result came up with "skin effect" and inductance. If it's not them. Please tell me why there is a non-zero AC resistance. Thank you.
     
  10. Oct 12, 2018 #9

    berkeman

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    Please give us links to the reading you have been doing about superconductivity, and point to any places in that reading where AC current effects are mentioned. You should probably try to understand superconductivity first at a basic level (by doing the reading), before asking slightly more advance questions about superconductivity here. Thanks.
     
    Last edited: Oct 12, 2018
  11. Oct 12, 2018 #10
    Because of what we know about superconductors.

    Tinkham, Introduction to Superconductivity
    Schmidt, The Physics of Superconductors
    van Duzer, Principles of Superconductive Devices and Circuits
     
  12. Oct 12, 2018 #11
    If you want a really precise answer: Mattis-Bardeen theory
     
  13. Oct 12, 2018 #12
    Zapper commented the above when I mentioned "skin effect"... but cyro's comment "If you want a really precise answer: Mattis-Bardeen theory".. but Mattis-Bardeen theory is related to skin effect.. from wiki:

    "The Mattis–Bardeen theory is a theory that describes the electrodynamic properties of superconductors. It is commonly applied in the research field of optical spectroscopy on superconductors.

    Introduction[edit]
    The Mattis–Bardeen theory [1] was derived to explain the anomalous skin effect of superconductors. Originally, the anomalous skin effect indicates the non-classical response of metals to high frequency electromagnetic field in low temperature, which was solved by R. G. Chambers.[2] At sufficiently low temperatures and high frequencies, the classically predicted skin depth (normal skin effect) fails because of the enhancement of the mean free path of the electrons in a good metal. Not only the normal metals, but superconductors also show the anomalous skin effect which has to be considered with the theory of Bardeen, Cooper and Schrieffer. "

    Now about AC resistivity of superconductors: https://sites.google.com/site/puenggphysics/home/unit-5/superconductors

    "9. AC Resistivity: The current in a superconductor in normal state is carried by normal electrons only. When the material changes from normal state to superconducting state, then few normal electrons are converted into super electrons which carry dc current in superconducting state without any electrical resistance. If a constant dc current is flowing in a superconductor, there is no resistance in the material; hence, no electric field in the material. If we apply dc voltage source to a superconductor [below TC], then current will not increase suddenly but at the rate at which the electrons accelerate in the electric field. This indicates the presence of electric field in the material. If we apply ac voltage source to the superconductor, then the superelectrons accelerate in the forward and backward direction; they lag behind the field because of inertia. Also under ac fields, current is carried not only by superelectrons but also by normal electrons; this adds resistance to superconductor [belowTC]. Under high frequency ac voltages, a superconductor behaves as a normal material because under ac voltages, electric field exists in the material that excites superelectrons to go into higher states where they behave as normal electrons."

    Isn't this "they lag behind the field because of inertia" is related to impedance?

    https://link.springer.com/article/10.1007/BF00618215

    https://en.wikipedia.org/wiki/Electrical_impedance
    "Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. The term complex impedance may be used interchangeably. "

    In my reply to Zapper, I mentioned skin effect and inductance. And he commented I'm shooting in the dark and hoping to hit something. So if it's not skin effect and impedance or inductance.. then what exactly has Zapper in mind of the cause of non-zero AC resistivity in superconductors??
     
  14. Oct 13, 2018 #13
    Skin effect and losses are not related to each other. Perfect electric conductors, an idealization often used in simulations, display perfect skin effect (all field stays at the surface), but show no loss.

    The explanation with lagging behind and mixture of normal/superconducting electrons is reasonable (at this level), but Mattis-Bardeen includes all of this
     
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