Yesterday I tried the the superconducting magnet‘s persistent switch again.
I failed to make a persistent superconductor, but all the circuits and LabView worked properly. More WIN than FAIL.
Conceptually this is the circuit we are testing. The heater functions as a variable resistor. The IGBT functions as the switch. Both are computer controlled.
This is the procedure:
I built a LabView VI to trigger the SC coil a variable number of millisecond after the heater:
We can measure the magnetic field produced with the DC magnetometer:
When I ran the experiment with 5A through the SC coil, I only saw a tiny magnetic field:
Furthermore, use of the heater seemed to make no difference at all.
As a control I ran the magnet in this configuration to see what magnetic field strength we should expect:
The produced a much stronger field:
So the full current is not going through the main coil, but through the heater. I suspect either the heater resistor is not working (I can hear and see it boil the liquid nitrogen) OR the splice in the coil has more resistance than the coil heater:
The last time I ran this experiment the YBCO corroded from condensation:
This time I ran 2A of current through the coil for several hours to warm and evaporate any moisture.