Possible Polywells

15 11 2010

All photos.

This diagram shows the possible coil configurations of the superconducting tape. Going from minor radius 2 mm at top to minor radius  7 mm at bottom.

I used the very cool XRVG to generate SVG diagrams from ruby.





PERSISTENT SUPERCONDUCTING MAGNET VICTORY!!!

21 10 2010

All photos.

I have put the superconducting magnet into a persistent state!!!!!

Power supplies off, magnet still going!

Details to follow.

UPDATE:

OK. Here it is. The units are in raw volts coming from the magnetometer and the current sensing resistor (0.008 ohms). The red is the current going into the superconducting coil, the white is the magnetic field. You can see that the current drops off, but the magnetic field persists. WIN!!!!

The magnetic field gradually falls off over the course of an hour.

This is the setup:

SC coil in the dewar:

Here is the schematic:

It was all controlled manually by switching the power supplies on and off.





Superconducting Magnet Test 3

21 10 2010

All photos.

I re-spooled the YBCO on it’s original spool. Hoping for a stronger magnet and less liquid nitrogen.

We ran 2A DC through the coil at room temperature and David searched for the strongest point of the field.

Which turned out to be the very center, perhaps amplified by the ferrous steel screw:

In this configuration we are seeing ~140 gauss magnetic field while running 5A DC current through the SC magnet submerged in liquid nitrogen (with no persistent switch short circuit):

Much better!

Next we re-fabricated the persistent switch… this time using a much longer splice, better soldering, and a longer heater directly over the splice:

We also included some heat shrink tubing to insulate the heater:

We will test this again today!





Superconducting Magnet Test

18 10 2010

All Photos.

I added another terminal to the superconducting coil.

It looks like this:

I operated the coil in the following configuration. About 12cm of SC cable was above the liquid nitrogen forming a resistor.

Putting 5A through the SC coil produced about 20 Gauss.

When I submerged the warm SC cable in liquid nitrogen (leaving the current source on), the field dropped off by half!

The strength of the magnetic field was sensitive to changes in the amount of YBCO at room temperature.

In summary:

We succeeded in directing the current into the main superconducting coil despite the short circuit. GOOD.

When we “turn off the heater” by dunking the warm SC cable into the liquid nitrogen, we lose much of the current going into the main coil.

Not exactly sure how to interpret the results.

My guesses for what’s needed:
1) Longer span of YBCO in the heater.

2) Insulate the heater.

3) Longer splice, better solder joint.





Superconducting Magnet Test

16 10 2010

All photos and videos.

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.

 

Superconducting magnet submerged in liquid nitrogen.

 

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:

6 Gausse from the SC magnet

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:

15 Gauss When connected directly.

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.





Superconducting Magnet

15 10 2010

All photos.

I’m almost ready to test the superconducting magnet again. The coil heater and the SC coil are wired up to Labview. The DC magnetometer is showing on a graph in Labview:

I’m still struggling with timed sequences in Labview. I want the SC coil to shutdown x milliseconds after the heater is turned off. I can’t use the wait vi because it stops the whole program.





IGBT

8 10 2010

 

All photos.

Yesterday I got the IGBT working under computer control. I switched my desk lamp on and off from my computer. The IGBT will be used to switch up to 90 Amps going into the superconducting magnet.

IGBT

Schematic:

Here is a video of the win:

From 2010-10-07







Follow

Get every new post delivered to your Inbox.

Join 660 other followers

%d bloggers like this: