Sunday, May 4, 2014

Can crusher you say?

This is just a quick post to point out that what I thought might be the bane of the H-ray project's existence two days ago my in fact be its saving grace.  Reading more about the can crusher built at the University of Maryland in 1994[1], I came across the following graph.



It appears that the apparatus can generate a greater than 10 kGauss field in under 40 microseconds.  We only require 800 Gauss, so the maximum field seems like a bit of overkill... until you start thinking about the required uniformity of the magnetic field used to make our superconducting sample quench.  Ideally, we'd like to have the entire sample quench at once leaving the spin currents hypothesized by Hirsch nowhere to go.  Hirsch[4] theorizes that the collapsing spin currents are responsible for the Bremsstrahlung radiation, (known as H-rays around here).  By quenching the spin currents everywhere in the superconductor, the number of  H-rays produced should be maximized.

Creating a uniform field of 800 Gauss or so over the entire sample which is a 3.8 cm radius sphere of lead is rather difficult to do using a simple solenoid.  It was this fact that led me to consider using the iron yoke magnet I spoke about in the last post[2].



While the rate of change of magnetic field is distressingly small with this magnet, at least the field is uniform over almost the entire 7.5 cm radius of the pole face, guaranteeing that the whole sample will quench at once,albeit slowly.

This brings us back to the can crusher coil.  It's a rather diminutive little coil consisting of only three turns as designed at U. Maryland.  It does however pack up to a 20 kGauss wallop at its center!  The question is, can it quench the entire volume of the sample at once?  I ran some numbers through our Mathematica[3] solenoid model and came up with the following graph


The y axis is in units of kGauss, the x axis is in units of meters.  The blue curve represents the magnetic field at the center of the solenoid, which is centered at x = 0 and perpendicular to the x axis.  The purple line is the field in kGauss required to quench the lead sample.  The field is high enough throughout the sample!

Of course, this brings back the can crusher issues of the last post in spades, but we can always switch over to an unsilvered fiberglass Dewar and avoid them!

References:
1.  AJP can crushing article, (sadly not open access)
http://scitation.aip.org/content/aapt/journal/ajp/62/1/10.1119/1.17739

2.  Previous post
http://copaseticflow.blogspot.com/2014/05/h-rays-mounting-dewar-in-magnet.html

3.  Mathematica code
https://drive.google.com/file/d/0B30APQ2sxrAYUDlfdTdJLVBBZEU/edit?usp=sharing

4.  Open access version of Hirsch's article on ionizing radiation from superconductors
http://arxiv.org/abs/cond-mat/0508529

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