Superconducting Magnet

15 10 2009

Gearing up for a second superconducting magnet test. This time computer controlled. Here is the new bobbin with 133 turns:

IMG_4262

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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:

IMG_3934

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

IMG_3933

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.

IMG_3937

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.





Progress Update

12 08 2009

Todd T. From Swagelok stopped by the shop and we quickly built a parts list for the deuterium system and the RGA. Turns out we are using a VCR style Swageloks, and they require a single use steel gasket much like the copper gasket in a conflat.

Also made a first pass at building the persistent switch. Here you see 50cm of insulated nicrome wire wrapped around 5cm of YBCO:

IMG_3915

Cover in Kapton tape:

IMG_3916

Connect a multi meter across the YBCO, and wire up the nicrome wire to a variable power supply:IMG_3920

And into the cold:

IMG_3921

Unfortunately I was not able to get any reliable readings from the ohm meter. Before I turned the heater on, the meter registered between -0.5 ohms to  0.4 ohms. Any change in resistance from turning on the heater was lost in the meters margin of error. However the heater does turn on and work. You can hear the LN2 boiling off when you set the heater current to about 1.5 amps. So not exactly sure how to meter and test the persistent switch… for all we know this one works. And really this makes perfect sense: the resistance of the multimeter probes should be greater than the strip of superconductor even in it’s resistive state.

Coming out of the LN2:

IMG_3922





Heater barrel working

23 01 2009

Hooray, we got the heater barrel working. Except I _thought_  JB Weld was safe upto 600˚C, but that stuff was smokn!  gross. We’ll have to redo it using proper fire cement. Here is a short video:








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