Some Quantized Flux History

In  1961, William Fairbank and Bascomb Deaver experimentally verified that magnetic flux can be quantized.  This week I read an excellent paper on the history of the experiment[1].  For those who aren't close to a library with access to the journal, (and for my own notes), here are a few of the highlights.  For more info on the Fairbank/Deaver experiment see[4] .

The Other Experiment

The first interesting thing you should know is that there was a similar experiment  performed in Southern Germany by Robert Doll and Martin Näbauer in the same year, (1961)[2].  Their apparatus was different,  instead of  vibrating a superconducting cylinder to determine the value of the magnetic field at had trapped as Deaver and Fairbank did, they used a superconducting cylinder attached to a torsion pendulum (picture 1).  By measuring the amount of time it took the oscillations of the pendulum to die off they were able to determine the strength of the trapped magnetic field.  Their results showed the same stepping of trapped flux that the Deaver/Fairbank experiment did.

The two experimental groups knew nothing about each others efforts until the representatives of each experiment met at the IBM meeting on superconductivity in  Yorktown Heights, NY.

The Theory Connection
Nina Byers and Chen Yang, (of Yang-Mills fame), were working down the hall from Deaver and Fairbank while they were working on their experiment.  The two theorists studied the results of the experiment and wrote up the theoretical explanation in an article that immediately followed Deaver and Fairbank article in PRL[3].  When Fairbank showed preliminary data of the quantized flux plateaus to Chen he thought the data set was jut linear in the manner that might be expected if flux wasn't quantized.  Fairbank explained to him that having taken the data he felt the experimenter could attach a sort of personality to each data point and almost subconsciously analyze the validity of each point.  The completed data set at the end of the experiment bore out Fairbank's initial impressions.  Byers and Yang are pictured below (picture 2).

The Cooper Pairs

Kind of surprisingly, from a modern perspective where Cooper pairs are a given, there was a contingent of physicists that felt the results didn't show quantized flux because the flux steps were twice as big as predicted by London.  What Byers and Yang had already pointed out and others were quick to reinforce was that the result made perfect sence because the charge carriers in the superconductors were Cooper pairs.  The BCS theory of superconductivity, (C stands for Cooper), published in 1957 had predicted that the charge carriers in superconductors were actually pairs of electrons, (Cooper pairs). In addition to verifying that magnetic flux could be quantized, the two experiments had also provided evidence of the hypothetical Cooper pairs.

References:

1.

http://dx.doi.org/10.1007%2Fs10909-011-0349-x
Einzel D. (2011). 50 Years of Fluxoid Quantization: 2e or Not 2e, Journal of Low Temperature Physics, 163 (5-6) 215-237. DOI: 10.1007/s10909-011-0349-x

2.  Doll and Näbauer experiment

http://dx.doi.org/10.1103%2FPhysRevLett.7.51
Doll R. & Näbauer M. (1961). Experimental Proof of Magnetic Flux Quantization in a Superconducting Ring, Physical Review Letters, 7 (2) 51-52. DOI: 10.1103/PhysRevLett.7.51

3.  Bauer and Yang
http://dx.doi.org/10.1103%2FPhysRevLett.7.46
Byers N. & Yang C. (1961). Theoretical Considerations Concerning Quantized Magnetic Flux in Superconducting Cylinders, Physical Review Letters, 7 (2) 46-49. DOI: 10.1103/PhysRevLett.7.46

4.  More meanderings on Fairbank
http://copaseticflow.blogspot.com/2013/05/thoughts-on-fairbanks-quantized-flux.html

http://copaseticflow.blogspot.com/2013/05/the-strange-story-of-free-fractional.html

GIGO and Lightning Formation (GIGO: Gammas In, Gammas Out)

Two recent lightning studies provide interesting insight into the formation of lightning and the terrestrial gamma flashes, (also known as dark lightning),  that sometimes accompany it[1][2][4].  While both studies make use of the radio pulses created during lightning formation they seem to differ in their explanations of how the radio pulses are created.

Lake Maracaibo from Wikipedia http://en.wikipedia.org/wiki/Catatumbo_lightning

First a little background on lightning formation.  The following great summary is from a recent post by +John Baez.[3]

"Lightning happens in stages. First, a streamer of electricity travels from one charged area to another, say, from a cloud to the ground, or from one layer within a cloud to another. This prompts a return stroke with the reverse charge to go in the opposite direction. The initial streamer electrified the air it moved through, creating a path of least resistance that allows the return stroke to carry a much greater current."

Both of the studies indicate that radio pulses associated with lightning are emitted from the thundercloud prior to the actual lightning, during the streamer formation mentioned above.  The two studies differ, however, in their attribution of the source of the radio pulses.  I'm a bit perplexed by the whole thing.  If there are any lightning experts that would like to chime in and clear everything up, that would be awesome!

Reference 1 details a study that was made possible by the coincidental detection of the same lightning flash over Lake Maracaibo, (picture 1), by two different satellites, (one of them was the satellite mentioned in [3]), as well as two different radio-based terrestrial lightning detectors.  By sorting out the signals from the various detectors, they were able to determine that the radio pulse took place shortly after the terrestrial gamma flash, (TGF), and they attribute the creation of the radio pulse to the gamma flash.

"We find that the TGF was produced deep in the thundercloud at the initial stage of an intracloud (IC) lightning before the leader reached the cloud top and extended horizontally. A strong radio pulse was produced by the TGF itself."[1]

The timing information agrees with the second study.  It's not made clear by the paper how the gamma flash created the radio pulse however.

The second study was based on lightning measurements made over Russia and Kazakhstan.  This project was concerned with measuring the same radio pulses mentioned in [1] in an effort to determine what initiates lightning creation.  Here's where we arrive at the GIGO model, (gammas in, gammas out).  The researchers present a model based on their data that indicates that the initial breakdown of the lightning conduction channel is caused by a cosmic gamma ray creating an ionization cascade.  They attribute the radio pulses, which they agree occur prior to the lightning, to the resulting high electron currents created by the ionization cascade.

Interestingly, the ionization cascade proposed by [2] for lightning formation is the same process used, (on a much smaller scale), in particle detectors known as wire chambers.  A high energy particle, (such as a cosmic ray), strikes an electron orbiting an atom of the gas filling the detector.  The electron is knocked out of its orbit ionizing the atom.  An electric field maintained in the detector accelerates the now free electron and it in turn ionizes additional gas atoms.  The electrons from these collisions ionize still more atoms and a cascade of electrons is formed which is detected by sensitive amplifiers built into the detector.

In particle detectors, if the cascade runs away and becomes too large it can damage the detector.  Special care is taken to make sure no small particles of dust or other pollutants are present in the detector as these can serve as nucleation points for further cascades. The Russian study indicates that small water and ice particles have the same effect in thunderclouds that dust has in wire chambers.  They serve as nucleation points that allow cosmic rays of lower energy than initially expected to create electron cascades that led to lightning strikes.

Thanks to  +Hans Havermann for pointing out the terrestrial gamma flash study!

All thoughts, comments, suggestions and clarifications are always welcome!

References:
1. Terrestrial Gamma Flash study
http://dx.doi.org/10.1002%2Fgrl.50466
Østgaard N., Gjesteland T., Carlson B.E., Collier A.B., Cummer S., Lu G. & Christian H.J. (2013). Simultaneous observations of optical lightning and terrestrial gamma ray flash from space, Geophysical Research Letters, n/a-n/a. DOI: 10.1002/grl.50466

2.  Russian Lightning study
http://dx.doi.org/10.1103%2FPhysRevLett.110.185005
Gurevich A.V. & Karashtin A.N. (2013). Runaway Breakdown and Hydrometeors in Lightning Initiation, Physical Review Letters, 110 (18) DOI: 10.1103/PhysRevLett.110.185005

3.  +John Baez's post on dark lightning
https://plus.google.com/u/0/117663015413546257905/posts/NmQqg63S2bp

4. Open access synopsis of the Russian lightning study from the +American Physical Society
http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.110.185005

Thoughts on Fairbank's Quantized Flux Discovery and the Quantum Hall Effect

William Fairbank might be most famous for experimentally demonstrating that magnetic flux is quantized[1].  In 1961 he published the results of an experiment that exposed very small cylinders of superconducting tin to a magnetic field and then measured the magnetic flux trapped by the cylinder after the applied magnetic field was turned off.  For more detail on why the flux was trapped, see [2].  He arrived at the following graph of trapped flux vs. applied field strength. (picture 1)

The data points are clustered around magnetic flux levels on the y axis that correspond to the values predicted for the magnitude of quantized magnetic flux.  The apparatus for the experiment is similar in several ways to the apparatus for the fractional charge experiment I mentioned yesterday [3].  A superconductor was exposed to an external magnetic field and results were analyzed by measuring properties of an induced vibration of the superconductor through a magnetometer, (an inductive pickup coil).

Almost three decades later in 1980, Klitzing experimentally verified the quantum Hall effect.  This is another effect due to the quantitization of magnetic flux.  His data was similar to the following[4].  Notice the naturally similar structure, (both experiments are measuring quanta of magnetic flux). (picture 2)

A few years later in 1997, it was experimentally verified that in a two dimensional electron gas, electrons could behave as quasi-particles with one third the charge of a normal electron.  The following data shows a plateau at a flux level corresponding to a charge of 1/3[5]. (picture 3)

My leisure time this week is probably going to wind up being spent wondering if the fractional quantum hall effect had anything to do with the fractional charge results Fairbank reported in 1977[3].  Does anyone happen to know if this has ever been addressed?  All thoughts, comments, and/or questions are always welcome!

A final note, Fairbank's constructed his quantized flux apparatus based on a vibrational magnetometer design published in 1959[7].  It's definitely my favorite piece of experimental equipment for the week.  The prototype was build from a loudspeaker, a drinking straw and a paper cup! (picture 4)

References:

1.  

http://dx.doi.org/10.1103%2FPhysRevLett.7.43
Deaver B. & Fairbank W. (1961). Experimental Evidence for Quantized Flux in Superconducting Cylinders, Physical Review Letters, 7 (2) 43-46. DOI: 10.1103/PhysRevLett.7.43

2.  Flux trapping on Copasetic Flows

http://copaseticflow.blogspot.com/2013/04/lenzs-law-induction-and-levitation.html

3.  Fairbank and fractional charge

http://copaseticflow.blogspot.com/2013/05/the-strange-story-of-free-fractional.html

4.  Quantum Hall review article

http://dx.doi.org/10.1103%2FRevModPhys.59.781
Yennie D. (1987). Integral quantum Hall effect for nonspecialists, Reviews of Modern Physics, 59 (3) 781-824. DOI: 10.1103/RevModPhys.59.781

5.  Fractional quantum Hall effect (open access)
http://rmp.aps.org/abstract/RMP/v71/i4/p875_1

6.  Scientific American on the Quantum Hall Effect
http://ist-socrates.berkeley.edu/~phylabs/adv/ReprintsPDF/SHE%20Reprints/21-Quantized%20Effect.pdf

7.  Fairbank apparatus progenitor
http://dx.doi.org/10.1063%2F1.1716679
Foner S. (1959). Versatile and Sensitive Vibrating-Sample Magnetometer, Review of Scientific Instruments, 30 (7) 548. DOI: 10.1063/1.1716679

The Strange Story of Free Fractional Charge

The currently widely held wisdom is that quarks, the subatomic constituents that make up protons and neutrons, cannot be found in an unbound state, (i.e. roaming freely outside of a proton, neutron, or other particle made up of quarks).  The reasoning goes that the attractive force due to the strong force between two quarks is so powerful that if they are separated far enough apart, there will be enough energy stored in the  strong field to create two additional quarks that will immediately glom on to the two you were trying to separate in the first place, hence, no independent unbound quarks.

In 1977, however, Larue, Fairbank[1], and Hebard reported that they had found evidence indicating that free quarks did in fact exist[2].  Their experiment involved suspending a 1/4 mm superconducting niobium sphere in a magnetic field gradient[7] and causing it to oscillate in a vertical direction.  The researchers measured the effects reversing the polarity of an applied electric field had on the sphere's oscillation frequency. Using this data, they were able to calculate how much free charge was present on the sphere.  They wound up with the charge data shown below [3] (picture 2)

The scientific community at large, at least those who remember the work at all, tend to remember the penultimate incident in the history of the experiment.  Luis Alvarez suggested that to remove any possibility that humans had tainted the data by performing subjective data cuts, random numbers should be added to a newly taken data set.  That data was to be 'blind' analyzed and the results were to be reported.  What most people will tell you is that the published results after this analysis were less than conclusive.  What they'll leave out or don't know is that the published blind results contained a number of disclaimers that the graduate students in charge of the project had setup the apparatus incorrectly and that most of the inconclusiveness could just as easily be attributed to this poor setup.  

In 1989 after two years of retirement, William Fairbanks returned to Stanford to perform more work on the fractional charge experiment.  Sadly, he died soon thereafter on a morning jog after spending the night before working on the fractional charge experiment.  In an obituary befitting the X-Files the New York Times reported

"Although Dr. Fairbank retired two years ago as physics professor at Stanford University, he had been at work there the night before his death, trying to verify his report of 11 years ago concerning the existence of individual subatomic particles called quarks."[4]

While there are claims that the experiment was reproduced by other researchers, there are interesting inconsistencies in their methods.

1.  The follow-ons weren't done at liquid helium temperatures

2.  A ferromagnetic levitation system utilizing iron covered niobium spheres was used instead of the superconducting levitation system used in Fairbank's experiments.

A few years later in 1997, quasi-particles, combinations of electrons that behave in manners inconsistent with the behavior of a single electron were found to exhibit charge equal to 1/3 that of an electron's.  Is it possible that the experimental results of Fairbank et al. were a macroscopic demonstration or this behavior?  Instead, did they actually see free quarks, or was it all just experimental error?  What do you think?

References:

1.  Other notes on William Fairbank

http://copaseticflow.blogspot.com/2013/05/gravitomagnetism-and-antigravity-for.html

2.  Fractional Charge Indicated

http://dx.doi.org/10.1103%2FPhysRevLett.38.1011
LaRue G., Fairbank W. & Hebard A. (1977). Evidence for the Existence of Fractional Charge on Matter, Physical Review Letters, 38 (18) 1011-1014. DOI: 10.1103/PhysRevLett.38.1011

3.
http://dx.doi.org/10.1016%2F0168-9002%2888%2991113-8
Phillips J.D., Fairbank W.M. & Navarro J. (1988). Recent results in the search for fractional charge at Stanford, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 264 (1) 125-130. DOI: 10.1016/0168-9002(88)91113-8

4.  New York Times Obituary for William Fairbank

http://www.nytimes.com/1989/10/03/obituaries/prof-william-n-fairbank-72-physicist-and-pioneer-in-quarks.html?pagewanted=1

5.  arXiv open-access version of the quasi-particle discovery [pdf]

http://arxiv.org/pdf/cond-mat/9706307.pdf

6.  National Academy of Sciences Bio of William Fairbank

http://nas.nasonline.org/site/DocServer/Fairbank_William.pdf?docID=79822

7.  Superconducting levitation
http://copaseticflow.blogspot.com/2013/04/lenzs-law-induction-and-levitation.html

Crystal Power: Benchtop Fusion Devices

A few weeks ago I wrote several background posts on low energy nuclear reactions, (LENR).  The vote is still out on whether or not LENR is conclusively showing results.  There's another type of bench top fusion device that is working though and it's based on a crystal.  In April of 2005, three researchers from UCLA reported in Nature the results of an experiment where they fused pairs of deuterium atoms to create helium three and a free neutron with an energy of approximately 2.55 MeV[1] (picture 1).  Their experiment was more of a benchtop particle accelerator than a benchtop fusion reactor.  Utilizing the natural properties of lithium tantalate crystals, they were able to ionize deuterium atoms and then accelerate them to energies of 115 keV.  The accelerated deuterons impacted a molybdenum target coated with an Erbium/Deuterium compound.  At the energies created, the deuterons were able to fuse with other deuterium nuclei to create the above mentioned reaction.  There's some interesting physics and history behind all this.

Quantum Tunneling
First of all, classically speaking about coulomb barriers, 115 keV isn't nearly enough energy to hurl one nuclei into another.  However, as pointed out by Gamow[2] and others, thanks to quantum tunneling phenomena, particles can tunnel through the barrier with much lower energies.  This is why the deuterons are able to fuse when accelerated to only 115 keV.  Both Cockcroft and Walton's linear accelerator and then Lawrence's cyclotron made use of tunneling to perform the first nuclear disintegrations.   It's interesting to think that they might have been able to accomplish a similar feat with a much more compact setup than either experimental team actually used.  For an excellent reference on the history of particle accelerators, see [3].

Pyroelectric Crystals
The crystal used in the experiment was made of lithium tantalate. This is a type of crystal that spontaneously polarizes and develops its own electric field as its temperature is raised.  Crystals with  this property are known as pyroelectric.  The inherent electric field created by these crystals is what was used by the UCLA researchers to provide the accelerating potential for the deuterons.

The fist reference I could find to research on the pyroelectric properties of lithium tantalate was in an article from Bell Labs' researchers B.T. Matthias and J.P. Remeika.  Their article was published in 1949 which puts this particular crystal outside the reach of both accelerator teams mentioned above who were doing their work in the 1930s.

You can grow your own pyroelectric crystals using Rochelle salt[7] (picture 2).  While to the best of my knowledge you can't use them to build accelerators as described above, they do have interesting piezoelectric properties.  In junior high, I grew a few crystals  in an attempt to  experiment with piezoelectricity . If you attach electrodes from two opposing crystal faces to a small neon bulb and then bang the crystal gently with a hammer you're supposed to be able light the bulb with a voltage created by the crystal.

Rochelle salt crystals can be grown in supersaturated solution.When I was growing them, Rochelle salt was still available as a laxative in some older pharmacies in town.  Trying to get enough raw material to grow a crystal, I had more than one pharmacist in Hobbs, NM wondering what a 12 year old kid was doing buying them out of their stock of old-school laxative.


Ferroelectric Hysteresis
Because pyroelectric crystals can have an inherent electric field independent of any applied electric field, they exhibit hysteresis in an applied electric field in the same manner that a ferromagnetic material does when a magnetic field is applied.  The term ferroelectirc was coined to denote the similar hysteretic behavior and doesn't necessarily denote the presence of iron in pyroelectric/ferroelectric crystals   The hysteresis curve for Rochelle salt is shown below[5]. (picture 3)

References:
1.  Nature article on bentchtop fusion
http://dx.doi.org/10.1038%2Fnature03575
Naranjo B., Gimzewski J.K. & Putterman S. (2005). Observation of nuclear fusion driven by a pyroelectric crystal, Nature, 434 (7037) 1115-1117. DOI: 10.1038/nature03575

2.  Gamow on tunneling
http://dx.doi.org/10.1038%2F122805b0
GAMOW G. (1928). The Quantum Theory of Nuclear Disintegration, Nature, 122 (3082) 805-806. DOI: 10.1038/122805b0

3.  An excellent masters' thesis on the history of the particle accelerator by Andrew Steere
http://bt.pa.msu.edu/pub/papers/steeremsc/steeremsc.pdf

4.  Lithium tantalate as a pyroelectric, (ferroelectric)
http://dx.doi.org/10.1103%2FPhysRev.76.1886.2
Matthias B. & Remeika J. (1949). Ferroelectricity in the Ilmenite Structure, Physical Review, 76 (12) 1886-1887. DOI: 10.1103/PhysRev.76.1886.2

5.  Rochelle Salt properties
http://dx.doi.org/10.1103%2FPhysRev.17.475
Valasek J. (1921). Piezo-Electric and Allied Phenomena in Rochelle Salt, Physical Review, 17 (4) 475-481. DOI: 10.1103/PhysRev.17.475

6.  More Rochelle Salt properties
http://dx.doi.org/10.1103%2FPhysRev.47.175
Mueller H. (1935). Properties of Rochelle Salt, Physical Review, 47 (2) 175-191. DOI: 10.1103/PhysRev.47.175

7. Rochelle salt crystals
http://www.madsci.org/posts/archives/2007-04/1176763406.Ph.r.html