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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: I was thinkin' posted by Penguin on August 31, 2005 at 18:50:31:
The main reasons to use a superconductor are current density and lack of dissipation.It is possible to get a kiloamp through a Niobium Titanium superconductor that is smaller than an 18 guage wire, even though 2/3rds of that conductor is copper. (the copper is for stabilization and current bypass in the event of a quench..it has almost no heat capacity at helium temps..).
The main issue, as Al stated, is the cooling. For LTS, like niobium titanium and niobium tin, the use of liquid helium is a deterrent...the last I checked, it was about 50 dollars a liter.
If you use HTS, yibco or bisco, you can use liquid nitrogen, which costa roughly 32 cents a quart..American Superconductor in Mass sells HTS. Unfortunately, they are currently scaling the production line up, so are not exactly gonna sell small consumers any, they are looking for superconducting magnet and power transmission line specialists to buy the stuff.
It is tape form, roughly 3/16 wide, and is a stainless tape with the hts film either in the middle for the neutral high strength product, or on one side. The neutral tape can take 50mm bends, while the one sided only 100 mm bends.
Both run about 150 amperes at 77 Kelvin, and for this application, are completely impervious to self field.
The disadvantage of supers? They are great, use em all the time at work..but, at some point, the current has ta get up to the room temp things, amp and speaker. If you use a beefy copper to get from 77K to 300K, you will have lots of heat being transferred to the cryo system, and there will be an ice ball where water vapor is freezing. so, large copper feedthroughs are a bane to the cold, but if you scale that down, you lose all the gains of lower system resistance.
You can bring the tapes very close together, but you will still have a flat tape pair, so will not entirely constrain the magnetic field. The HTS is not amenable to coaxial construction, so you can't contain the field that way.
And you cannot forget, the smaller the conductor, the more external inductance it will have (recall the log (d/r) component of the inductance equation..decrease r, the conductor radius, and the inductance goes up.) Luckily, at the current densities of audio, the current doesn't really penetrate very deep, so the internal inductance is almost nil..but that could only buy you 15 nHenry per foot anyway..
So any benefits you could get by using supers to their advantage, will be lost (and then some) when you try to get the current out of the cold environment, and back up to room temperature. I've not seen a coaxial gas cooled feedthrough that can support low resistance and still remain somewhat gas-tight.
It'd be a lot more advantageous to build a #10 awg concentric coax. You'd have very low resistance, extremely low inductance, and by selecting the dielectric, keep stored energy down..
Cheers, John
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Follow Ups
- Hi dee - jneutron 10:35:14 09/01/05 (2)
- Hey, sorta what i was looking for - Penguin 17:26:38 09/01/05 (1)
- No prob - jneutron 06:24:41 09/02/05 (0)
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