Getting Back to Basics, Generating the Quenching Magnetic Field

A question from +Yannick Selles inspired today's post which is a rerun of the answer I posted yesterday on G+ with a few more pictures and an additional book reference.  I blame the evil stomach spirits that attacked for the lack of originality :)  Yannick asked how the magnetic fields required to drive the superconducting samples into their normal states, (quenching), for the H-ray experiment, were generated.  Here are the basics

When an electric current travels through a wire, it creates a magnetic field surrounding the wire.

By wrapping a wire into a coil, (a solenoid), the magnetic fields from each turn of wire align to produce a stronger magnetic field.  The black cylinders you see in the picture of the magnet below are solenoids of copper wire.  The black casing carries water to cool off the wire since it also heats up as current is passed through it.

If you want to make an even larger magnetic field, this is where a material like iron comes in.  Iron is made up of magnetic domains that align when they are placed in a magnetic field.  Consequently, when you wrap your coil around iron, not only do you get the field from the coil, you also get the aligned field of all the magnetic domains in the iron.

Here's a picture of the original coil wrap of my cyclotron magnet.  The wrap was scrapped for a more uniform job later, but it gives you a clear picture of the wrapping of the coil onto the iron pole pieces.

The metal you can just barely see in the center of the black wire cylinders is iron.  The metal painted blue is also iron.  Magnetic fields prefer to stay in iron in much the same way electric currents like to stay in wires.  It' the easiest path for them to move in.  We capitalize on this by surrounding the pole pieces with an iron frame that you can see better here:

In this manner, as much of the field as practically possible is focused between the two cylindrical pole pieces.﻿

Entire books have been written on magnetic circuits including this one, (open access on Google Books), by a historical figure I've been researching, Dr.Vladimir Karapetoff of Cornell University.

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.

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

Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla

to the nabla for another coordinate system, say… cylindrical coordinates.

What we’ll need:

1. The Cartesian Nabla:

2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:

3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:

How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

Lost Phone

We were incredibly lucky to have both been in university settings when our kids were born.  When No. 1 arrived, we were both still grad students.  Not long after No. 2 arrived, (about 10 days to be exact), mom-person defended her dissertation and gained the appellation prependage Dr.

While there are lots of perks attendant to grad school, not the least of them phenomenal health insurance, that’s not the one that’s come to mind for me just now.  The one I’m most grateful for at the moment with respect to our kids was the opportunities for sheer independence.  Most days, we’d meet for lunch on the quad of whatever university we were hanging out at at the time, (physics research requires a bit of travel), to eat lunch.  During those lunches, the kids could crawl, toddle, or jog off into the distance.  There were no roads, and therefore no cars.  And, I realize now with a certain wistful bliss I had no knowledge of at the time, there were also very few people at hand that new what a baby…

Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…