Prometheus Fusion Perfection

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!

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.

All photos.

The persistent switch on the superconducting magnet needs a computer controlled heater. The heater itself is just a coil of nichrome wire around the YBCO:

With some experimentation I determined that it takes about 300 mA to make the heater warm to the touch.

Now I want to computer control the heater using a digital output on the NI USB 6008. The 6008 will control a higher current transistor (or darlington) and the transistor will control the current to the heater.

Seeing that the NI USB 6008‘s output is either +5V or 0V, my first instinct was to try this:

This failed. FAIL.

I looked at the docs for the NI USB 6008 and I found this:

The default configuration of the NI USB-6008/6009 DIO ports is open collector, allowing 5 V operation, with an onboard 4.7 kΩ pull-up resistor.

So basically the digital output  is either an open circuit or a path to ground. The 4.7 kΩ pull-up resistor brings the output to +5V when it’s ON, but when you ammeter from DO1 to ground you don’t see any current.

However in this configuration you will see a current turn on and off with DO1:

How do we go from a current to a voltage? A resistor!

This schematic represents the working solution:

Here is a video of computer controlled current:

From 2010-09-30