Sunday, July 27, 2014

Leak Detector Testing... Again Lab Book 2014_07_27


Summary:
The leak detector stopped working correctly several weeks ago.  It didn't exactly depart his mortal coil so much as just stop being useful.  Sort of like a major league baseball catcher hunkered in a hockey goal.  It looks sort of like it has the right equipment, but it obviously incapable of performing it's tasks in any sort of meaningful way.  It boils down to this, the mechanical roughing pump is still pulling a vacuum that should enable the diffusion pump, responsible for doing the detailed vacuum work, to switch on, and yet the diffusion pump abjectly refuses.

If you're new to the experiment, the background of what's going on here in broad strokes can be found at the bottom of the post.

Lab Book 2014_07_25     Hamilton Carter

Leak Detector Work

Leak detector testing was resumed.  The first test was to check the vacuum on the end of the vacuum hose coming from the roughing pump and normally attached to the diffusion pump, but now attached to a thermocouple gauge.  The vacuum pulled down to 150 mTorr after several minutes.

The second test was to move the roughing pump path selector from the right hand path to the diffusion pat as shown in the figure above to the left hand path into the space evacuated for leak detection.  To do this, the smaller knob is turned clockwise until the white dot on its face points along the left hand path  Their was no vessel to be leak detected attahced on the left hand path.  The path was merely attached to the thermocouple gauge.  The vacuum pulled down to 30 mTorr in less than a minute.  After two more minutes, the pressure was down to 27 mTorr.  Checking the right hand path again after this, it was found that the vacuum pulled down to 50 mTorr.  The hose connection to the thermocouple gauge may have been leaky.

Next, the hose form the roughing pump was reattached to the diffusion pump  The pump was run for a minute or so on the right hand path attachd to the diffusion pump.  There is no guage attached to that side to read the vacuum, so after the first minute, the path knob was changed to the left hand path.  The thermococuple guage indicated a vacuum of < 10 mTorr immediately.  After another minute, the vacuum was down to 4 mTorr.  During this test, the built-in meter shown above read a pressure of .4 mBar.

The large valve knob that opens the diffusion pump to the left hand path was opened.  No change in the vacuum was observed.  In a later run, a brief change in vacuum to a pressure of 11 mTorr was observed but after 1.5 seconds, the pressure reduced again to its original value. 

To make sure the valves were working correctly, the trap was opened as a coarse check of its vacuum pressure.  There was an inrush of air consistent with the vessel holding a vacuum before being opened.

The indicator light for < 10^-2 on the panel of the leak detector was never lit.  It’s beginning to appear that either the pressure gauge built into the leak detector is broken, or there is damage to the control circuits that light the indicator on the front panel.  I don’t believe the bulb is out because the diffusion pump never heated up, even after being plugged back into power.


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: