Monday, February 16, 2015

Systems Testing: Lab Book 2015_02_16

Work is proceeding on testing the systems that will be used in the experiment.  While the glass Dewar’s silvering blocks gamma radiation in the 22 keV range substantially, it fits nicely inside the yoke magnet whose field can be easily measured.  A temperature gauge was located; vacuum testing was started for the inner Dewar and lid, (including the instrumentation ports.)  Scroll to the bottom for the background of the experiment.

All about the temperature gauge
Today, just pictures of the gauge.  For an idea of scale, its rectangular footprint is about the size of a nickel.  The four wire sockets on the left are for attaching a four point probe to measure the resistance of the gauge.





The Dewar lid with all the attachments
The easiest way to seal the Dewar lid was to put the instrumentation stick back in place.  An experimental stage to hold the Pb sample still needs to be designed.


Testing the vacuum pump before testing the Dewar
In order to reduce the number of variables when the lid is tested, the recently serviced vacuum pump was tested independently.


The vacuum pump is working well:

Exhaust hosing for the leak detector pump is currently stored behind the red toolbox.

Procedure for pre-cooling the Dewar with liquid nitrogen
1.       Fill the Dewar with liquid nitrogen
2.       After the inside has cooled, pump the evaporating nitrogen gas out via a roughing pump
a.       Monitor temperature as pressure is reduced
b.      If the reading stabilizes, solid nitrogen has formed.  Pressurize with dry nitrogen gas
c.       If the reading continues to drop as the pressure drops, the Dewar is evacuated



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

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