Thursday, March 28, 2013

Notation and Cryostat Design

I took the first look at the cryostat that is probably going to use for the hole theory of superconductivity experiment.  A cryostat is a vessel for holding a coolant or cooling system, (in our case, liquid helium), and the equipment/samples for an experiment.  Because helium transitions from a liquid to a gas at just over four degrees Kelvin, the cryostat has two walls separated by a vacuum space to insulate the liquid helium inside from the room level temperatures outside, just like a thermos.

Before I get to much further into the details of the cryostat, I'd like to coin a phrase.  As those of you who already read the proposal for the experiment[1] know, Dr. Hirsch of UCSD has proposed a new model for superconductivity[2], and one of the predictions made by that model is that superconductors will emit Bremsstrahlung radiation[3] when they are quenched back into their normal non-superconducting state.  It's getting to be a bit much to type Bremsstrahlung all the time, or the 'hole theory of superconductivity for that matter, so I'm going to coin a phrase with apologies to Dr. Hirsch.  From now on, to have less to type, I'll just call the project the experimental search for H-rays.  It's good to get the notation fixed.

Now, on to the cryostat!  The bore diameter of the cryostat is about 5 1/8 inches.  The planned size of the Pb sphere to be used is 3.8 cm which comes in at about 3 inches, so it should be a pretty comfortable fit.  The bore depth is roughly three feet, so there's plenty of room for the superconducting solenoid that will provide the required 800 Gauss to quench the superconducting Pb back to its normal state.  There are a few pictures of the cryostat shown below.

Looking into the top of the cryostat with the lid removed (picture 1)

The side view of the cryostat (picture 2)

Looking into the cryostat (picture 3).

I have to design an instrumentation header, (lid), for the cryostat.  At the moment, I know it needs the following

1.  Two ports to supply and exhaust first, liquid nitrogen and then liquid helium

2.  Either on or two ports for bringing supply leads to the superconducting magnet.  See below for more information.

3.  A port for the liquid helium level detector as well as the thermometer leads.

4.  Support structure for the superconducting solenoid.

5.  Support structure for the Pb sample.

More on Magnet Design
It was brought up today that while the superconducting solenoid could handle 50 amps, more heat would be created by the normal conducting leads that had to deliver the current into the cryostat.  More heat means more boiled liquid helium and less run time.  By upping the number of coils in the solenoid, I can reduce the current requirement, but then the inductance will go up it will be harder to change the magnetic field quickly.  There are trade-offs to be made before the final design is put in place.

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

2.  Hirsch on the hole theory of superconductiivity
http://dx.doi.org/10.1103%2FPhysRevB.71.184521
Hirsch J. (2005). Spin currents in superconductors, Physical Review B, 71 (18) DOI:

3. Ionizing Radiation from Superconductors
http://dx.doi.org/10.1088%2F0953-8984%2F19%2F12%2F125217
Hirsch J.E. (2007). Ionizing radiation from superconductors in the theory of hole superconductivity, Journal of Physics: Condensed Matter, 19 (12) 125217. DOI:

4.  Ionizing Radiation from Superconductors on arXiv
http://arxiv.org/abs/cond-mat/0508529v2
J. E. Hirsch (2005). Pair production and ionizing radiation from superconductors, J. Phys. Cond. Matt. 19, 125217 (2007), arXiv:

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