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.


21 10 2010

All photos.

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

Power supplies off, magnet still going!

Details to follow.


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.


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.



Here is a video of the win:

From 2010-10-07

Coil Heater

30 09 2010

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

Liquid Nitrogen

28 09 2010

All photos.

Gearing up for another test of the superconducting magnet. So liquid nitrogen.

What is this… Halloween?

Heat Shield

1 12 2009

The red hot fusor grid reminds me  - I must address thermal issues from plasma, xrays and neutrons for polywell fusion without boiling the superconductor’s liquid nitrogen.

I asked for help with thermal modeling on the polywell talk forum. Good feedback.

Here is a rough draft of the superconducting magrid with a vacuum separated heat shield:

The trick is, the shield must have a gap so that you can weld the lid to the chassis. The welded magrid would have a gap in the shield along the midplane of the torus.

This gap would bring the vacuum between the heat shield and the inner superconductor holder. Well actually it would be  ~10 mToor of ionized deuterium.

This design does not include liquid water cooling. Although it’s easy to add cooling channels with the Arcam process, the real challenge is connecting fluid channels when you weld the lids onto the chassis.


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