Wednesday, July 30, 2014

Leak Detector Down but Not Out, Code Crusher Code Objectified! Lab Book 2014_07_29


Alternate Title:  How Could Something So Pretty be So Broken?

Summary
It finally became too cumbersome to work with the can crusher simulation code in script form.  the bulk of this morning was spent in meetings and reworking the can crusher code to be object oriented.  The object oriented refactoring was completed and tested and works great!  It’s now very easy to run multiple simulations and compare their results.  The next step is to write code that runs the simulation to the peak current point and then plots the magnet field in on a spherical surface that will correspond to the surface of the superconductor Pb sample being used.  There are other simulations that need to be done as well.  For example, finding out how the current traces change when the temperature of the material is 4.2 K, the temperature of liquid helium.

The leak detector problem has been isolated.  The Pirani gauge that measures the vacuum on the diffusion pump side of the system has burned out.  Since it shows no vacuum in its burned out state, the diffusion pump is never turned on by the leak detectors control logic.  The Pirani gauge is literally a light bulb with the top cut off and its measured resistance varies as a function of the pressure of the air the bulb is immersed in.

Scroll down for background on the experiment.
Can Crusher Code
Moved the can crusher code implementation to object oriented from the Python script based version.  The code is now much easier to test with the ability to instantiate multiple simulations to compare results. 

Vacuum Leak Detector Work
The thermocouple gauge was attached directly to the gauge port on the liquid nitrogen trap.

The gauge that was is installed on the liquid nitrogen trap during normal operation is an Alcatel PI 1, see picture below.  This is a pirani sensor and may be the source of our problems.  For more information on the sensor, see http://dalibor.farny.cz/helium-leak-detector-running/  and https://en.wikipedia.org/wiki/Pirani_gauge


The bulb should have a cold resistance of 70 ohms.  Ours measures as an open circuit.  It seems the bulb is burned out.

Background
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.  My experiment will look for H-rays emitted by both a Pb and a YBCO superconductor when it is quenched by a strong magnetic field.
This series of articles chronicles both the experimental lab work and the theory work that’s going into completing the experiment.

The lab book entries in this series detail the preparation and execution of this experiment… mostly.  I also have a few theory projects involving special relativity and quantum field theory.  Occasionally, they appear in these pages.

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

References

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


No comments: