Superconductor Key Questions

Discussion in 'General Electronics Chat' started by henry newton, Aug 2, 2008.

  1. henry newton

    Thread Starter Member

    May 5, 2008
    Q1. It is a known fact that direct current can flow undiminished forever in a superconductor ring or toroid. Superconductors also conduct alternating current, but with some slight dissipation of energy.My question is how long does it take for alternating current to decay to say half its initial value in a superconducting toroid.

    Q2. What type of DC current flows undiminished forever in a superconductor ring or toroid.Is it a constant DC current like the type obtainable from a battery or varying DC current obtainable from a rectified AC current or both.

    Q3. MEISSNER EFFECT shows that superconductor is diamagnetic, that is it REPELS a magnetic field regardless of the pole that is brought to it (no attraction whatsoever).This effect or property is nicely demonstrated by levitating a small bar magnet above the surface of a superconductor DISK . This has become the classic experiment demonstrating the Meissner Effect.

    MY question is if an electromagnet is formed by using a superconducting Solenoid or better still Toroid with either a AIR or SOFT IRON CORE placed inside the solenoid or toroid, and then cooled with liquid nitrogen in other to take it it's superconducting state.Will the superconducting electromagnet behave like a typical electromagnet that attracts or repels a bar magnet depending on whether unlike poles or like poles of the superconducting electromagnet and the bar magnet are brought close to each other. OR will the superconducting electromagnet exhibit the MEISSNER EFFECT, whereby it repels a bar magnet regardless of which of its pole ( i.e the bar magnet) is brought close to the poles of the superconducting electromagnet.

    Q4.How much gauss or Tesla (if there is any) can a soft iron used as the core for a superconducting electromagnet tolerate.In other words is there a critical gauss or Tesla level that could destroy the magnetic property of soft iron used as a core for superconducting electromagnet.

    Q5.How much power is required by cryogenic refrigerator or cryostat for cooling superconductor.Is there one that could be powered by say between 100watts and 500watts of electricity.
  2. Wendy


    Mar 24, 2008
    Unless it is a resonant circuit, superconductors do not store AC in any form. They store DC because of the magnetic field that forms from the current. With a resonant circuit, the capacitor may be one loss, but I suspect the big loss is from the radiated energy in the form of photons (think antenna). Storing AC is not practical.

    The core, whether air or iron, doesn't aquire any special properties because it is inside a superconducting torroid. It might interact with the magnetic field, but that's it.

    The gauss and current that a superconducter can take is independent to some degree, and entirely dependent on the superconducting material. Different materials have different values.

    I have no idea how much energy it takes to make cryo nitrogen, but it is pretty cheap. Most industries that use nitrogen have it delivered in cryo state, and thaw it as needed.
  3. bertus


    Apr 5, 2008

    In my job we use liquid helium to cool down the magnet coil.
    The current brought into the coil will stay there until the helium is below a level called 0% filling.
    100 % filling is a full dewar of helium.
    For isolation there is a shield filled with liquid nitrogen.
    We have magnets with a fieldstrength upto 14 tesla.
    This is a foto of a nmr system with the superconducting NMR magnet.