Friday, May 9, 2014

Lab Book 2014_05_09 Experiment Planning, Scotch Tape X-Rays, and Rotational Line Elements

Lab Book 2014_05_09     Hamilton Carter               
Most of today was spent researching and planning what tasks needed to be done and when.   The only lab work was measuring the more of the dimensions of the fiberglass Dewar and checking on a source for replacement Dewars.  If we’re able to use YBCO, (a type of high temperature superconductor), to prototype the experiment with liquid nitrogen I spent some time determining how the low energy x-rays, (H-rays), could be detected.  One of the possibilities is just to use x-ray film as a type of integrating detector over several runs.  Another possibility s to setup the NaI detector to detect a lower energy spectrum.  The NaI avenue may be blocked to us because of the thickness of the permanent metal window installed around the NaI crystal.

On the theoretical side of things, I spent some time making sure that Franklin’s line element for a rotating frame in special relativity matched with Takeno’s.

Dewar seals
I checked the seal on the fiberglass Dewar that has already been placed into service.

The manufacturer of the seals, Bay Seal  Co. still exists if we need to get replacements.

I found a good looking resource on using NaI as an x-ray detector even at low energies in the single and tens of kV.

Experiment Planning
As it turn out, the proposed Pb sample size will fit in the fiberglass Dewar with the pulsed magnet coil attached.  While it would be nice to confirm quenching of the sample at liquid helium temperatures using the uniform field of the iron yoke magnet, the fiberglass Dewar tail is only 6 3/16” long which will not allow the sample to be placed between the magnets pole pieces.  The magnet coils block the wider Dewar chamber from being lowered between them.
Since we won’t be in position to take delivery of liquid helium until later in the summer, all protyping tests will be run with liquid nitrogen and the YBCO sample.  While the predicted energy and flux are much lower for the YBCO superconductor, the activities will provide an effective and cheaper test bed for our experimental protocols.
The YBCO sample that is to be used is shown below

Hirsch’s predictions depend on the spherical radii.  The largest whole sphere that can be constructed from the material is about 6 mm in radius, consequently, that number is being used as the radius parameter.  If the larger overall diameter of the sample winds up being significant, all the better.
The following is a listing of tasks that need to be performed in roughly the order listed to complete the experiments.

Glass Dewar Leak Detection
This may be put off until later in the project.  The YBCO samples may be cooled in the Dewar, but… Actually, this may still be the best first activity.  Even using only liquid nitrogen, it would be nice to have a vacuum jacketed Dewar.  If we use this Dewar for YBCO quench  characterization, then we’ve tested the vacuum jacket and won’t burn off quite as much liquid nitrogen in the process.  We cannot use the Dewar for YBCO H-ray detection however because the silvered lining will present too great of an attenuation barrier to the very low energy x-rays predicted for this sample size in YBCO, (~10 keV).

Modification of Lab Table for Dewar and Magnet Installation
The bottom shelf of the lab table will need to be removed.  A box has been located to place the glass Dewar in that is currently housed in the table while the work is done.  The bottom shelfof the lab table will be removed and a reinforcing brace between the front two legs will be placed in after the magnet is rolled in below the table.  A new hole will be cut in the table top so that the glass Dewar can be lowered between the poles of the magnet.  The pertinent dimensions showing that the magnet will fit below the table are shown below.

Yoke Magnet Characterization
I first need to leak test, the water cooled power supply for the magnet and setup the cooling attachments for the magnet itself which have been removed.  The interior of the magnet power supply is shown below.  Each of the large black tubes is a water supply line for the cooling manifolds

The magnet will be used to test the quench field of the YBCO sample.  If the sample won’t quench in the 7 kGauss range, then I have to rethink the rest of the procedures.  The yoke magnet will also be used in testing slow quench behavior of the YBCO and for slow quench behavior of Pb if a second smaller Pb sample can be obtained, or the Dewar can be modified to extend its tail.
YBCO Quench Measurement
Using a four point contact arrangement as described in “Handbook of Superconducting Materials, Volume 2” the quenching field of our YBCO sample can be measured assuming it’s below about 7kG or so, (the maximum field the magnet can provide).  The figure below shows the four-point arrangement.  The procedure is describe in yesterday’s lab book entry.

YBCO Sample Preparation
It looks like Electrodag, (a type of sliver paint), can in fact be used to make the four point measurement contacts to the YBCO sample.
NaI Scintillator Characterization in the Dewar
This can be held off until later since it is for use with the Pb sample and the fiberglass Dewar containing liquid helium.  It is however, a relatively easy task, so can be substituted in during any delays.  There’s also the possibility per the Scotch tape article and its associated pyroelectric fusion article in Nature that the NaI crystal can be used to detect the few kV x-rays, (colloquially known as H-rays), from the YBCO. 

The x-rays may not be able to make it through the rather thick window on our NaI detector.  Here's a plot illustrating the point.

Scotch tape video:

Takeno line element in comparison to Franklin’s
I’ve written this down in a LaTex document, so I’ll just cut and paste the results here.  The line element is how distance is measured in a given space.  In Euclidean space, it amounts to the Pythagorean theorm, the sum of the squares of the sides equals the square of the hypotenuse.  For flat space time, roughly the same formula holds but in a hyperbolic geometry.  The upshot of this is that either the time side of the triangle, or the space side winds up with a negative sign.  The choice of which side to make negative is somewhat arbitrary.  In what follows, the mismatches of negative signs that are mentioned are caused by the arbitrary selection of the space vs. time negative side.  In non-Euclidean space, which both Takeno and Franklin are working in, the Pythagorean formula can also have terms with sides multiplied by each other as opposed to themselves.

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