Re: [Phys-L] maglev

[Bernard Cleyet <bernardcleyet@redshift.com>]

On 2014, Apr 01, , at 14:24, Bill Norwood <bnorwood111@gmail.com> wrote:

> -In the old demo one swings a disc of aluminum thru a U magnet and sees
> considerable damping because of the eddy currents.
> -But there would have been no damping with a superconducting disc, right?
> -So, if the resistivity of the iron were less than that of the aluminum,
> would this lead to less damping if an iron disc were used? There would
> still be eddy currents in the iron, right?


Curiously iron wires are (were) used in the old HV transformers using an interrupter***. (Ruhmkorff and auto spark)  Not so modern ones use sheets (laminates?) to reduce Foucault loss.  Modern ones use toroids. and high frequency.   (DC => DC)

Instead of waiting for JD, I’ll “stab”.

Meisner applies to all supers?   

And it’s a balance between skin and conductivity.  Bill:  cheque this by cooling the disk w/ LN2.  Try different thicknesses and material including SS.


bc warned to not use too great a frequency, because of skin effect in the wave guide.  (ESR, EPR — X-band)  I think we settled on 17Hz.  

*** To prevent Foucault currents, which cause energy losses, the iron core is made of a bundle of parallel iron wires, individually coated with shellac to insulate them electrically.   

Induction coil - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Ruhmkorff_coil