Superconducting Magnet Test

19 08 2009

Today we ran the first test putting current through the superconducting magnet. First step is wiring up an AC connection for the DC power supply (0-100VDC, 0-120 Amps):

IMG_3928I learned how to crimp. It’s easy, but you need the right crimping tool. This power supply uses 240V single phase on the AC input side. I include these rather mundane steps because they matter. They need to be done for the project to move forward; they need to be done well; they often have their own challenges, “right ways”, tricks and considerations. I learn more than I expect from the simple stuff like connecting a power supply.

So here is the superconducting magnet soldered to a 50 amp twisted copper cable for main power, and the persistent switch with it’s nicrome heater wires:


On the other side we have the probe for the magnetometer secured with Kapton tape:


Here is the whole setup with a high wattage power supply for the main superconducting current and a low wattage power supply to power the heater coil. Dewar flask below.


Magnetometer check:

IMG_3939OH. Speaking of this magnetometer: I found out today that it drops -42 gauss when you dip it in liquid nitrogen. At first I though my gauss meter was broken from falling off the table!

So here is how it went:

First we lowered the experimental apparatus into the dewar of liquid nitrogen. It took several minutes for the nitrogen to stop boiling.

Next we turned on the heater up to 1 amp, based on previous experimentation. From there we incrementally raised the amperage, waiting about 1 minute between steps. The good news is the superconducting magnet seems to work. Here are the magnetometer readings for each amperage (adjusted for the -42 G drop from cryogenic):

5 A: 58 G

10 A: 126 G

15 A: 183 G

20 A: 232 G

So far so good!

Next we tried putting the magnet into persistent mode by turning off the heater allowing the persistent switch to become superconducting again.

Upon turning off the heater, the magnetometer jumped from 220 G to 115 G with no change in amperage to the magnet.

From here I lowered the amperage to zero over 10 seconds. The magnetic field returned to baseline. In other words FAILURE – the current did not persist.

Stuart suggest the problem may be that we are leaving the power supply connected, and it’s acting as a resistive load. We can certainly test this by adding a circuit breaker at the power supply.

So… not a complete success, but we have moved the game forward. I learned a lot today. I plan to retool this experiment, get some fresh LN2 and try it again.




One response

29 09 2009

I think the persistence is destroyed if you solder the connections and ends of the coil together as the solder is not superconducting.
I would try stripping the super conductor ends and crimping them together. You may only need to wrap a short section around a power resistor to destroy the superconduction for the switch.
Hope this helps.

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