Perhaps the quantity of flux or flux density does not change (perhaps), but there is most certainly a disturbance in the coil's magnetic field via flux path and/or density change in a non-symmetrical fashion.
I have some experience with Type2 superconducting coils and I can tell you that the magnetic flux density (B) definitely changes in response to the approach of a permanent magnet and can be picked up by a magnetometer probe in the bore or near it. However, none of the surface integration exercises that I've done on it indicated that the magnetic flux (Φ), which penetrates the bore, changes in response to that external field disturbance. This will (or should) generate a superimposed emf across the coil's finite resistance and burn off energy until the disturbance (changing flux path or density) ceases.
After the event the coil's energy should therefore be reduced due to the heat loss in the resistance.
It doesn't have the time to burn off the energy of the disturbance before the discharge stage, because the resistance is so small and the time constant is so long. To date, the time constant of a SC magnet has been proven empirically to be at least 23 years by the Belgium’s Membach Geophysical Station and the theoretical estimates are at 100000 years. ...and superconductors chilled below the "vortex glass temperature" are claimed to truly have zero resistance. In order to burn off some extra energy in the resistance, the current would have to increase during the event.
But the current, after the attraction of the soft ferromagnetic slug, decreases. This can be even demonstrated with resistive coils, that attract slugs (or their core halves) during time periods, which are much shorter than their initial time constant (Tau). Agreed, and I envision it slightly different than you have drawn.
After the event, the slowly declining current (appearing flat) will have stepped down a level.
Could you draw that in MSPaint ? What I am not certain about, is how the disturbed current of a pre-charged coil, will affect the coil's subsequent discharge of energy.
Can you clarify this question?
It was not a question, I was merely writing what I was uncertain about. The scenario, to which my statement referred to, progresses like this: - SC solenoidal coil getts pre-charged with current,
- the coil becomes shorted,
- the coil attracts a soft ferromagnetic slug into its bore from afar (which disturbs the coil's current but not the flux which penetrates its bore),
- that disturbed current gets quickly discharged into a capacitor.
« Last Edit: 2023-11-16, 03:10:19 by verpies »
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