Friday, May 2, 2014

H-Rays: Mounting the Dewar in the Magnet

I'm deeper into the planning for this summer's experimental search for H-Rays[1].  I've abandoned my previous superconducting magnet designs in favor of a much simpler pre-existing yoke magnet that's sitting out in the hallway.



The pole pieces are in the center of the picture and are retractable using the knobs on the edges of the magnet.  The resulting gap between the pole pieces is where the Dewar will sit,see the picture below:



The Dewar sitting between the pole pieces has created a new theoretical issue.  It's only theoretical for the moment though.  Once we have numbers to go with the theory, we'll find out if our Dewar will wind up looking like this[3][4]:



As +Peter Terren can tell you, rapidly changing magnetic fields like we hope to generate for quenching our superconducting sample will cause Lenz's law eddy currents that create opposing magnetic fields and resulting forces applied to the surfaces that contain the conductors.  What's an aluminum can got to do with a liquid helium Dewar you ask?  The inner jacket of the Dewar is coated with a reflective layer of silver to help with insulation.  If you've got an old coffee Thermos, look inside and you'll see the same thing.  The concern is that the silvered layer will carry induced currents just like the aluminum cans above and create stresses on the glass Dewar.  Our saving grace, hopefully, is that our magnetic field isn't too large and we just won't be able to move it too quickly given the hugely inductive iron magnet pictured above.  That's also one of our problems because we need a quick quench.  Tradeoffs.  Expect to see some back of the envelope calculations here soon.  In the mean time, does anyone know of a completely clear glass Dewar like the one shown below in this classic '60s liquid helium demo movie from Alfred Leitner[4]?



References:
1.  http://copaseticflow.blogspot.com/2013/03/open-science-is-cool-in-concept-but.html

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

3.  Sites addressing can crushing ala magnetic fields
The DeVry IEEE demo site
http://members.tripod.com/extreme_skier/cancrusher/

Tesla DownUnder
http://tesladownunder.com/Links.htm#Tesla Links

(Home of +Richard Green and previously +Jonah Miller), CU can crushing
http://physicslearning.colorado.edu/ldl/demo5K20.65

4.  Liquid helium demo
http://youtu.be/7U4hQ_Y9_Jk?t=3m27s


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