Tuesday, May 27, 2014

LabBook 2014_05_26 Superconductor Quenching Magnet Chilling Supply and Leak Detector Testing

Superconductor Quenching Magnet Cooling Supply Work
The magnet that will be used to quench the superconductor in our experiment is water cooled.  So is its power supply.  The water chiller that will provide the cooling was checked out and filled.  The plumbing to the supply was constructed and tested.  Two of the water lines required SwageLocks rather than Parker fittings to prevent leaks.
The superconducting sample is to be placed in a liquid helium Dewar during the experiment.  Work is being done to check the status of a second Dewar that can be used as a backup to the first.  At present, the leak detector for this work is not functioning properly.  Some time was spent on debug of the system with no conclusive answers found.

New to the game?  Scroll to the end for background on what this is all about.

Leak Detector Debug
Looking into why the leak detector no longer pulls down to < 10^-2 Torr quickly, (at all?).  Cleaned the liquid nitrogen trap which did have a little bit of pump oil in the bottom.

This didn't seem to help so the next step was to switch the mechanical pump onto the portion of the leak detector system that attaches to the system under test so that the pressure could be read off the system under test pressure valve.  The pump immediately began to evacuate the volume and in under a minute was down to:

After several minutes, the vacuum had reduced to a better, but still not satisfactory value:

The next step will be to switch the pump back to the normal diffusion pump backing position and fill the liquid nitrogen trap with a little bit of liquid nitrogen.  If there really is a trap-vapor problem, this should make things better.
This will have to wait until tomorrow because we’re out of liquid nitrogen and it’s a holiday.

Three Phase Circuit
Did a simple calculation to verify that the voltage measured between one line of the three phase switch box and the neutral will give us what’s expected.  The calculation was done by adding the voltage phasors of two different lines which will be 60 degrees out of phase with each other.  Phasors are vector added.  The process is shown below.

Magnet Supply Cooling Water
The reservoir of the chiller was filled.  Access to the reservoir is on top of the chiller under a Styrofoam cap.  Although it looks small, the reservoir will hold over a gallon of water.  In order to fill the various pipes in the laboratory spanning system, several gallons of water are required to be added to the reservoir.

The return hose on the water chiller interface was extended using a Parker lock fitting and the supply and return hoses were attached to the chiller using Parker fittings.  The pieces of a Parker fitting and the initial assembly are shown below:

As it turns out, no Teflon tape is required for Parker fittings.  The fully assembled hose extension fitting worked like a champ.

The supply and return lines both leaked with Parker fittings.  They were changed out to SwageLock fittings, a different brand with plastic rather than brass ferrules, and the leaks stopped.

The water supply and return system that feed the tubes to the magnet power supply are shown below.  The upright cylinder is the flow meter.  Our current flow rate is one gallon per minute which exceeds our half gallon per minute requirement.

Hirsch's theory of hole superconductivity proposes a new BCS-compatible model of Cooper pair formation when superconducting materials phase transition from their normal to their superconducting state[1].  One of the experimentally verifiable predictions of his theory is that when a superconductor rapidly transitions, (quenches), back to its normal state, it will emit x-rays, (colloquially referred to here as H-rays because it's Hirsch's theory).

A superconductor can be rapidly transitioned back to its normal state by placing it in a strong magnetic field.  The experiment being performed proposes to look for H-rays emitted by a Pb superconductor when it is quenched by a strong magnetic field.

The lab book entries in this series detail the preparation and execution of this experiment.

Call for Input
If you have any ideas, questions, or comments, they're very welcome!

1.  Hirsch, J. E., “Pair production and ionizing radiation from superconductors”, http://arxiv.org/abs/cond-mat/0508529 

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