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HT Superconductors

  1. Jun 6, 2005 #1

    Art

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    Given that HTSC cables have been commercially available for some time now why has the uptake of this technology been so slow. Even allowing for the extra cost I'd have thought the advantages such as 140x the current carrying capacity, far higher efficiency etc. would outway any possible disadvantages?
     
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  3. Jun 6, 2005 #2
    how high a temp are we talking about..?
     
  4. Jun 6, 2005 #3

    Art

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    I believe around 40K which is the big advantage over LTS which require cooling to 10K. Thus instead of requiring liquid helium which is expensive they use liquid nitrogen which is cheaper than bottled water. As I understand it the coolant is built into the cable in some permanent way.
     
  5. Jun 6, 2005 #4

    ZapperZ

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    Er.. no. LN2 has a boiling point of 77 K. So the operating temperature will have that as the maximum Tc for the superconductor to use LN2 has a coolant.

    HTS such as YBCO has Tc of around 92 K. So this isn't the problem. The problem with most HTS is that it has a low current density, and so a low critical current density, beyond which, it becomes normal, when compared to conventional superconductors. Furthermore, as a Type II superconductor, there's problem with migrating vortices and flux lines when there's any significant magnetic fields (as there usually is when there's current carrying conductors or if it is placed in RF fields). These tend to cause many parts of the superconductor to not be superconducting.

    One should also note that the higher the operating temperature, the less the density of supercurrent there is in the superconductor. What this means is that even if one is still below Tc, at elevated temperature, there will be more normal-state charge carriers present than at very low temperature close to 0K. While the DC resistivity of the superconductor will still be zero (since any potential applied will be "shorted" by the supercurrent), the AC resistivity of ANY superconductor is not zero. Here, the normal charge carriers/electrons also participate in the AC resistivity. So if you have a larger density of normal electrons at elevated temperatures, even if you're still in the superconducting state, you still lose power in AC transmission. For HTS, this is made worse because it is not a good normal state conductor in the first place - all HTS are doped ceramics.

    This, among other things, have made the technological application of HTS very challenging.

    Zz.
     
  6. Jun 6, 2005 #5

    Art

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    Thanks Zz,
    I misread the article, it referred to the first HTS material discovered operating at 40K but the critical temperature for the material they are using is 108K. :blushing: Where I am coming from is I was looking at a company as an investment opportunity and I wondered why if they had what reads like such dream products they weren't flying out the door. For example their literature boasts of ships engines they're developing for the US navy 1/4 the size and 1/5 the weight of equal power conventional engines. It sounded too good to be true :smile: .
    With current technology limitations do you think it is likely the applications for superconducting products will always be limited or would straightforward solutions such as RF shielding around the cable alleviate some of the problems you described?
     
    Last edited: Jun 6, 2005
  7. Jun 6, 2005 #6

    ZapperZ

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    There have been limited applications of HTS - I think cell phone stations use them in some form or another. Any application that doesn't require a large current would tend to be more suitable. However, unless they can make major progress in the fabrication technology (and recent developements appear to make headway), the use of HTS will be technologically hampered by the limitations I've mentioned.

    From my perspective, as a physicist, the physics of HTS is more interesting since that has been what I've focused on. Even if we solve the technological issue, I don't think we'll ever see the end of new and exciting physics coming out of the study of HTS.

    Zz.
     
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