If you're new to the experiment, scroll to the bottom for background that will catch you up with what's going on.
Liquid Nitrogen Fill
The
liquid nitrogen Dewar has been filled.
It’s initial and final weights were 146 and 170 pounds, respectively. I’m guessing I must have read the initial weight
incorrectly, but we may be paying too much for ’45 liters’ of nitrogen which
might be closer to 13.
liters/pound
|
0.5606
|
||
start
|
146
|
||
finish
|
170
|
||
net
|
24
|
Total Liters
|
13.4544
|
I’m
doing the same measurement as yesterday with the sample immersed in liquid
nitrogen. There seems to be no
change.
I
have however invented a reasonably good vibration detector for the vacuum pump
across the room, see video here.
I’m
going to try a new configuration of the two coils next. Pancake coils will be constructed with one placed
on each of the opposing flat faces of the sample.
Checking resistance of
lead sample
Resistance
of leads was 0.0544 ohms, the resistance with the lead block between the leads
was too close to be able to tell the difference.
Back to work on the
quench detector
With
the large melt growth YBCO sample and a a set of solenoidal, (not pancake), coils,
the normal state results are quite different. The x axis of the plot below is the output
voltage that drives the primary coil.
The y axis of the plot is the signal from the pickup coil on the opposite
face of the superconductor. The
signal generator is set at a frequency of 5000 Hz.
It
should be noted at this point that the slope of the major axis of the above
loop is very dependent on the orientation of the top coil. Care was taken to
ensure that the top coil didn’t move significantly during the experiment.
imag0153
is the room temp result. 0155 is
completely cooled. 0156 is with half of
the liquid nitrogen evaporated and the upper coil once again suspended freely
by the wires. In other words, in the
last picture there is no possibility of the liquid changing the orientation of
the upper coil.
0153
|
|
0154
|
|
0155
|
|
0156
|
Turning
on the signal after cooling gives roughly the same results. The first photo is room temp. In the second photo is with the sample has
been cooled to its superconducting state
We
need more data. It doesn't seem to make
sense that the pickup signal became larger after the liquid nitrogen was
added. First off, this did not happen
with the other setup from yesterday.
Secondly, with the superconductor expelling field from its interior, I
thought the amount of flux through the pickup coil would have been reduced. There is a possible explanation. The liquid nitrogen should have also reduced
the resistance of the primary coil allowing it to pull more current from the oscillator
supply. The increased current would lead
to a larger magnetic field. Tomorrow the
current will be measured with the coil at room temperature and at the
temperature of liquid nitrogen.
*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.
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.
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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