SuperConductivity: Research & Findings & Thoughts

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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby StefanR » Tue Jul 01, 2008 3:12 pm

A Brief Introduction to Geomagnetism

The Earth's magnetic field is both expansive and complicated. It is generated by electric currents that are deep within the Earth and high above the surface. All of these currents contribute to the total geomagnetic field. In some ways, one can consider the Earth's magnetic field, measured at a particular instance and at a particular location, to be the superposition of symptoms of a myriad of physical processes occurring everywhere else in the world.
http://www.thunderbolts.info/forum/phpBB3/viewtopic.php?p=7561#p7561

Not authoritive of course, but still. :?
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby webolife » Tue Jul 01, 2008 3:56 pm

StevenO said:
"...matter, which itself is 3 dimensional energy (3D rotation). As a result currents through matter induce magnetism and vice-versa. However, this mutual induction does not happen in free space!" (webolife's underline)

:?: Why not... is there not 3D rotation happening in free space... and yes, the "edge" of "free space" I think does matter here.

Reading through the Dewey Larson bit, I remained unchanged in my proposition that space is a superconductor. What am I missing?
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby junglelord » Tue Jul 01, 2008 5:21 pm

I also agree that the EU is a coherent, charged, entangled, scalar reverse EM, quantum system. It is a BEC at the negitive energy level according to Dirac. That would follow the same rules of a superconductor.
:D
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby Solar » Thu Jul 03, 2008 7:28 am

webolife wrote:Reading through the Dewey Larson bit, I remained unchanged in my proposition that space is a superconductor. What am I missing?


I'm so very tempted to agree with this. It seems apparent that some planets demonstrate aspects of superconductivity and that the principle may be scalable:

-'induced' magnetic field' which seems to correlate with "flux expulsion"
-telluric currents which seem to correlate with "surface currents" of superconductors
-auroral and equatorial electrojet(s) which seem to correlate with "screening currents"
-the abundance of water and wood which are known to be diamagnetic
-the earth's dielectric atmosphere which functions as an 'insulator'

MGmirkin wrote:
Solar wrote:So the question is: As with superconductivity and diamagnetism can the earth's magnetic field be primarily the result of induction from the Sun's ("applied") magnetic field as opposed to the iron core/dynamo theory etc? When coupled with ground-to-cloud and cloud-to-ground lightning demonstrating the "penetration depth" of dendritic avalanches (positive and negative) the induced magnetic field of the earth so "opposes" the "applied magnetic field" of the Sun.

All of which would demonstrates the "self organizing" characteristics of electro-plasma dynamics. Or something to that effect.


An interesting question, but if one attempts to extrapolate a similar hypothesis to other planets, one encounters Mars which has no "magnetosphere" to speak of. Only what amounts to remnant crustal magnetism, and then only in the southern hemisphere to any large extent. How would the theory account for that? Does Mars have telluric currents as well?

Just a thought. Any theory of the like should be consistent across the multiple disparate bodies in the solar system. Is there something which would cause Mars to no longer have a magnetic field in any large extent? Is Mars electrically "damaged," as someone had asked once upon a time, such that it no longer functions correctly electrically? Or is something else going on?

~Michael Gmirkin


Interesting. Lets see what happens with that.

Super conductors are divided into two categories, type-I and type II. In type-I superconductors the magnetic induction inside the superconductor is Zero (B=0) and via a first order transition it goes into normal metallic state. In type-II superconductors the energy of an interface between a normal and a superconducting region is negative. This implies that it is energeticall favorable for these materials, when placed in an external magnetic field to subdivide into alternating normal and superconducting regions.


In comparison to the (theoretically) sharp transition of a Type-I superconductor the lower temperature Tc1, magnetic flux from external fields is no longer completely expelled, and the superconductor exists in a mixed state. - Wiki


Therefore, with type-II superconductors one would not expect an 'induced' ordered magnetic field but a "mixed state" wherein some areas exhibit 'induced' or diamganetically 'expelled' magnetic fields and other areas would have lower to nonexistant magetic fields. Of course there would then be abrupt and/or subtle transitions from one area to the other "...on Mars the direction of the magnetic field changes dramatically from place to place."

Dust Devils:

Note that "... magnetic field penetrates into these materials as quantized vortex filaments." The analgolous "penetration depth" at planetary scales would make this a crustal phenomena.

-Dust devils would be analgoulous to "quantized vortex filaments". Now an interesting thing to consider with this comparrison is that in order for surperconductivity to remain the vortices *cannot* move. In order to acheive consistent superconductivity "defects" must be added to the superconducting material to "pin" the vortices. Dust devils on Mars appear to occur on flat plains i.e. no "pinning" sites:

Adding defects can "pin" the vortex in place and restore zero resistance


Compared with:

Dust Devils at Gusev, Sol 525

It would make for an interesting comparison of areas prone to dust devil activity and the local magnetic field streagth of those same regions to contrast with that crustal magnetism map. Tornado alley type relationships come to mind.

As far as the Martian south pole and it's magnetism is concerned I suspect that it's electric functionality is no different than that of the south pole of Enceladus. However, because of the dry ice cap, iron rich soil, thin CO2 atmosphere etc the Martian south polar "plume"-like activity simply has a different characteristic of expression at it's electric navel.

For comparative 'insulating' dielectric breakdown see:

Lightning Strike on Mars

Electric Dust Devils on Mars

I would also venture in relation to the Martian south polar supposed "geyser" activity that some of the "holes" produced in the dry ice cap are the result of "pinned vortices" i.e. the penetration of magnetic field lines which would then result in the production of diamagnetic "expulsion" or 'induction' of the magnetic field in that area. Again, like Enceladus the polar regions are the touchdown points for the planetary electrical umbilical cord. As a result there will probably always be greater stability and pronouncement of electrical influences in polar regions.

Mars does have aurora: Mars Express discovers aurorae on Mars

By analysing the map of crustal magnetic anomalies compiled with Mars Global Surveyor’s data, scientists observed that the region of the emissions corresponds to the area where the strongest magnetic field is localised. This correlation indicates that the origin of the light emission actually is a flux of electrons moving along the crust magnetic lines and exciting the upper atmosphere of Mars.


The same relationship exist though different only with respect to "the region of the emissions corresponding to the area where the strongest magnetic field is localized." The relationship still stands save for localization of the diamagnetic superconducting aspect. The aforementioned "mixed state".

Therefore, these factors seem to indicate that Mars 'act' like a type-II superconductor.
"Our laws of force tend to be applied in the Newtonian sense in that for every action there is an equal reaction, and yet, in the real world, where many-body gravitational effects or electrodynamic actions prevail, we do not have every action paired with an equal reaction." — Harold Aspden
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby junglelord » Thu Jul 03, 2008 7:45 am

That was brilliant....WOW....
:shock:
Rep for that post big time Solar.
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby StefanR » Thu Jul 03, 2008 12:46 pm

Solar wrote:
webolife wrote:
Reading through the Dewey Larson bit, I remained unchanged in my proposition that space is a superconductor. What am I missing?


I'm so very tempted to agree with this. It seems apparent that some planets demonstrate aspects of superconductivity and that the principle may be scalable:

-'induced' magnetic field' which seems to correlate with "flux expulsion"
-telluric currents which seem to correlate with "surface currents" of superconductors
-auroral and equatorial electrojet(s) which seem to correlate with "screening currents"
-the abundance of water and wood which are known to be diamagnetic
-the earth's dielectric atmosphere which functions as an 'insulator'


-So what kind of space is discussed here? Can space without charge-carriers be conductive to currents?
-Would it be better to compare the flux expulsion/telluric currents/surface currents with surface/volume resistivity?
-aren't water and wood dielectric?
-If earth's atmosphere is an insulator because of dielectricity, what does it insulate from? And how does that relate to diamagnetism?
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby MGmirkin » Thu Jul 03, 2008 2:12 pm

junglelord wrote:Then consider that the Fair Weather Current is operating all the while the air is acting as a dielectric


Yes, but in what mode is it operating? Dark mode, glow mode, or arc mode? I'd suggest "dark mode," IE, a slow seep of current insufficient to transition to "glow mode" (Auroras & some other upper atmospheric phenomena) or arc mode (lightning, etc.)...

I don't think the fair weather current is a large barrier to understanding things electrically... IE, there's apparently always a bit of a voltage potential between the Earth & the atmosphere and/or space. It just usually is of a low enough magnitude that it's not readily perceptible to us (as auroras or lightning are more so). If we could better see the full range of electricity and magnetism, things might be a bit different.

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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby webolife » Thu Jul 03, 2008 6:10 pm

Permittivity of free space.
Conductivity can be defined as lack of resistance, which generally describes space.
Electrical/Magnetic fields alter this conductivity, as well as gravitational fields.
Stuff is not needed to "conduct", only a path of less resistance.
What am I missing?
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby junglelord » Thu Jul 03, 2008 6:31 pm

Conductance of the aether.
:D

Conductance of the Aether and Strong Charge
The Aether conductance constant (Cd) shows to be a factor of Coulomb’s constant and its relationship to the other known constants of the “vacuum”.
Cd = kc X e0/c X μ0
Where e0 = Vacuum permittivity, also called permittivity of free space or the electric constant is the ratio D/E in free space.
μ0 is the magnetic constant.

Cd = 2.112 X 10^-4 (sec X coul^2/kg X m2)

scant literature exists describing the conductance of the Aether (vacuum, free space, quantum foam), and modern physics. Conductance is the measure of a materials ability to conduct electric charge. Electrons do conduct through the Aether, as observed when electrons travel in the space between the Sun and the Earth. Electrons also pass through Aether in a vacuum tube. The conductance constant is a specific measure of the Aether's ability to conduct strong charge.


In quantum measurements, the conductance constant notates as
Cd = e emax^2/m(e) X Lq^2 X Fq

Conductance of the Aether is also equal to
Cd = e emax^2/h
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby webolife » Thu Jul 03, 2008 6:47 pm

Thank you, JL. I don't speak aetherese, but your quite tidy summation there shows me (once again) that we have two models explaining the same thing in different jargon, a finding that keeps me listening, sometimes hearing, and occasionally agreeing with what you have to say.
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby StefanR » Tue Jul 15, 2008 2:26 pm

Breakdown

Lighting is omnipresent in our modern world and most of the time it belongs to this category of things which are just there to make our lives easier and more comfortable. When you flick a switch the light goes on in the room you just entered. Probably this little action was done unconsciously and you do not even remember it a second later. Nevertheless, it is mildly irritating if a fluorescent lamp flashes a couple of times before burning steadily and it is the nightmare of a mayor of a big city to have the flood-lighting in an soccer stadium stay dark just before an important game.
Image
[ Bliksem ] A large group of lamps use gas discharges to generate light. A gas discharge is a neutral gas which has been made conducting by applying a sufficiently large voltage across it. This conducting medium comprises a wide range of different particles: apart from the neutral gas atoms, one can find electrons, ions and the many excited species which are responsible for the emitted light. The interplay between the different atomic and molecular constituents in this complex mixture and their interaction with electro-magnetic fields and surfaces makes gas discharge physics a challenging subject. Transforming the initially non conducting gas into a conducting medium is called breakdown and comprises an involved set of transient processes which is poorly understood even in the present day.

Gas discharges are used in many applications, ranging from, for example, surface treatment of materials to gas cleaning and indeed to lighting. Furthermore, gas discharges are omipresent in natural phenomena such as lightning, the polar light and many extraterestial processes such as stars and interstellar clouds.

In some of these occurances of gas discharges, breakdown is not an issue at all. Many, however, rely on breakdown. In light sources it is of course important that the light actually switches on. The way in which this process occurs furthermore has its influence on life time and production costs. However, in the tiny discharges that constitute a pixel in a plasma television, it is of fundamental importance how the discharge switches on: this is done many times per second.

In some of the research conducted at our institute, we ask what happens during the breakdown of the gas and why. In the following, the various interrelated projects are discussed:


Ignition of fluorescent lamps
[ CFL ] Compact fluorescent lamps (cfl) are nowadays often used as replacements for incandescent lamps (the regular light-bulb) because of their higher efficiency and longer lifetime. A compact fluorescent lamps needs several hundreds of volts to be ignited and only about one hundred volt to burn. This large ignition current is responsible for most of the electronic components in the base of the lamp. Knowing what determines the ignition voltage could therefore be interesting for lamp manufacturers. And, from a broader perspective, understanding ignition of discharges in general is in itself very interesting indeed.
Image
[ CFL ignition ] In order to be able to separate the various mechanisms that could play a role in a real cfl, the system is simplified to a straight glass tube, operated on a DC voltage. On the left one can see a `film' of iCCD camera pictures taken of such a lamp by Maxime Gendre. The electrode at 0 cm is the cathode, the one at 14 cm is the anode. At t = 4 microseconds after the voltage has been applied, an ionisation front starts to move from cathode to anode. When it reaches the anode (at about 12 microseconds) a `return strike' fills the tube with a fairly homogeneous emission. From then on it will take some time (several tens of microseconds) before the current rises and the lamp can be said to have ignited. Depending on the conditions striations can be observed.
Image
[ CFL model ] By modelling the system (see the false-colour map of the calculated emission on the right) we think we gained a fair understanding of what happens in the phase in which the ionisation front moves from cathode to anode.


http://www.einlightred.tue.nl/index_en.html
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby StefanR » Tue Jul 15, 2008 2:28 pm

Electric fracture: growth and branching of ionized channels (CTF.6501)

Project nummer: ctf6501
Omschrijving van het onderzoek

Streamer-like electric discharges form the initial stage of electric breakdown in long gaps; they are ubiquitous in nature and technology. They appear in St. Elmo's fire and recently discovered sprite discharges above lightning clouds and determine the early stages of sparks and lightning. They are used in corona reactors for dust precipitation, ozone generation, disinfection of water and air, odour removal and various other applications. They also play a role in the (re)ignition of high pressure gas discharge lamps. The action of streamers on a gas or other substrate is three-fold: 1) They carry electric current and create a path for further electric breakdown; on their course, they deposit charge in the system that, e.g., can be used for electrostatic precipitation of nanoparticles. 2) They generate high energetic electrons in a thin space charge region; these electrons very efficiently catalyze gas-chemical reactions and even lead to X-ray emission. 3) They might convect the gas through which they are moving.

This project aims to a coordinated experimental and theoretical study of the initial phases of electrical breakdown in gases. The goal is to obtain a thorough physical understanding of the process that will enable us to optimize various technological applications. The methods include detailed theoretical and computational models developed at CWI Amsterdam, time resolved measurements of streamer width, velocity and branching under carefully determined physical conditions in a wide parameter range at the physics department of TUE, and the development of a large scale pulsed power corona system at the electrical engineering department of TUE. The electrical engineering department also supports the experiments at the physics department with power supplies operative in the 10 to 60 kV range while experiments in the MV range are carried out in the electrical engineering lab. Two major applications are under investigation: bad odour removal from exhaust gases and tar removal from biogas.
http://www.stw.nl/Projecten/C/ctf/ctf6501.htm
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby StefanR » Tue Jul 15, 2008 2:42 pm

Latest results
ICCD imaging of breakdown
Time-resolved ICCD images were made to study the general characteristics of the breakdown phenomena. The breakdown conditions were:

* Argon gas, pressure: 465 Pa (3.5 Torr)
* Electrode spacing: 3.3 mm
* Top electrode powered, bottom electrode grounded
* Applied voltage: pulsed positive, 350 V maximum, 100 ms pulse length, rise time 30 ms, repetition rate 500 Hz

Figure 1 shows the measured applied voltages and the discharge current.

Figure 1: Applied voltage pulse and discharge current
The intensifier gate width was set to 100 ns and images were taken with different time delays after the start of the voltage rise. The results are shown in figure 2.
Image
Figure 2: ICCD images of breakdown
These ICCD images show the characteristic features of breakdown at low pressure. From 32 to 35 ms, a moving light front can be observed, which crosses the electrode gap and covers the cathode surface. This light front can be associated with an ionization front, a moving region of high electric field with considerable ionization and excitation processes. A moving ionization front is one of the fundamental building blocks of plasma breakdown at low pressure.

The ICCD images also show a weak light flash (9-17 ms) before the main breakdown phase and subsequent plasma development. During this time, the applied voltage is rising, but still below the breakdown voltage. More detailed studies showed that this light flash is caused by electron avalanches seeded by volume charges left over from previous discharges.
http://www.phys.tue.nl/EPG/epghome/projects/breakdown/breakdown_files/Results/Results.htm
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby StefanR » Wed Jul 23, 2008 3:11 pm

Let me just add this here because of the relation with the dielectric stuff some posts above:

Plasma Dynamics and Diagnostics
Self-organised structures in planar dielectric barrier discharge systems

Self-organised structures belong to the first phenomena observed in gas discharge systems and aroused due to their enormous variety peoples interest. The most famous example certainly are the Lichtenberg-figures.
In this project, self-organised structures in a planar, dielectric barrier discharge system with large lateral extension are investigated. The variety of observed structures range from homogeneous discharges to striped patterns and labyrinths as well as to filamentary discharges. In the latter case, single filaments can be regarded as particle like structures creating due to their interaction new, more complex patterns, like e. g. hexagonal arrangements, rings or quasi-molecules.
From the point of view of gas discharge physics questions concerning the creation and stabilisation of these structures in a glow mode discharge are posed and become approached experimentally and numerically. The most important experimental tools are the observation of the light emitted by the discharge and the measurement of the surface charges emerging on the dielectric surfaces. For the surface charge measurement a BSO crystal is used as a dielectric barrier and via the electric-field-dependent birefringence of the crystal the surface charges are detected.
Image
Image
Furthermore the observed structures become embedded in the framework of nonlinear dynamic and hence questions concerning macroscopic models and mechanisms are posed. By statistical evaluation of pattern dynamic properties of filament motion and interaction can be investigated.
http://www.ipf.uni-stuttgart.de/gruppen/pdd/pdd_structures.html
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Re: SuperConductivity: Research & Findings & Thoughts

Unread postby StefanR » Sat Aug 02, 2008 7:28 am

Magnetic Flux in Superconductors
by Jan Kycia
Dept. of Physics, University of Waterloo


In 1911, Kamerlingh-Onnes liquefied helium. This
allowed him to study the properties of materials at lower
temperatures than those ever obtained before. Soon after,
a student in his group unexpectedly discovered
superconductivity in mercury. A superconductor can
conduct electricity with no resistance or heat dissipation.
By measuring the resistance of mercury at low
temperatures, the electrical resistance was found to drop
to zero below 4.15 degrees kelvin (K). Many other
materials were later found to become superconducting,
such as lead, niobium, aluminum and tin. Rules of thumb
came about for predicting which materials would
superconduct. Although nowadays many novel
superconducting materials have been found that do not fit
easily into any of these categories, these rules of thumb
were very useful to researchers in the past. One rule was
that the material had to be metallic. Another rule was that
in general, poor electrical conductors at room temperature
would have the highest superconducting transition
temperature, (Tc). Below the transition temperature, the
material becomes superconducting. Aluminum is a good
conductor, and its Tc is about 1 degree kelvin. Lead is a
poor conductor, so its Tc is about 7 K. Gold, silver and
copper do not superconduct at any attainable temperature.
Another rule of thumb was that magnetic materials
do not become superconducting. For example, iron and
nickel do not superconduct. The reasoning here is that the
superconductivity and magnetism compete with each other
since both involve order to produce a lower energy state.
All superconducting materials have a critical magnetic
field, Hc, above which they stop superconducting. There
are many ways to test the properties of superconducting
materials and the phenomenon of superconductivity itself.
The order in which the experimental parameters are changed
can drastically change the final state of the superconductor,
as the final state is “history-dependent”.

One way to test the superconducting properties of
a material is to make a ring of the material and study its
response to magnetic fields. If you had a superconducting
ring in zero magnetic field, T< Tc, H = 0, and then a
magnetic field was applied perpendicular to the plane of
the ring, by Lenz’ law, with no resistance in the ring
material, a current would be induced, flowing to exactly
cancel the change in magnetic field. So the magnetic field
inside the ring would always be zero. If you keep raising
the field, the counteracting current keeps increasing until
the superconductivity breaks down and the material goes
normal. That is, it becomes resistive and all the magnetic
field lines go rushing into the ring so that the magnetic
field becomes uniform.

Now, you can field-cool this ring, which means you
apply the magnetic field to the ring while the material is at
a temperature above Tc, then cool the ring below Tc. The
magnetic field inside the ring is fixed to be what was
initially applied, even if the externally applied magnetic
field is varied. Even if you lowered the magnetic field to
zero and turned off the magnet, a counteracting current
would be running around the ring to exactly maintain the
original magnetic field. This current can persist in a
superconductor indefinitely, as long as it remains
superconducting. Since there is no resistance, it is
predicted that the electrical current could continue running
for at least 108 years.

The research community has determined that two
classes of superconductors exist: Type I and Type II. They
are differentiated by the way they deal with a magnetic
field when they are field-cooled. Lead, which is a Type I
superconductor, will go normal above a critical magnetic
field of about 1000 gauss (i.e. Hc = 1000 gauss). Imagine
field-cooling a thin foil of lead with a magnetic field
perpendicular to the foil. For very low levels of magnetic
field, all the field lines will be expelled from the lead foil
and the magnetic field inside of it will be zero. This field
expulsion is called the Meissner effect. However, as the
magnetic field is increased, it will require too much
energy to bend the magnetic field lines (this energy is
called the bending energy) such a long distance from the
center of the thin foil all the way to the edge. The thinner
the foil and the larger the foil area, the lower the magnetic
field that can be expelled. Above a certain field, the
superconductor breaks down and allows field lines to
penetrate it at the middle of the foil. This minimizes the
bending energy. The magnetic field inside the normal
region happens to have a field of exactly the value of the
critical field, Hc. Now, as the magnetic field is increased
even more, more of these regions are required to reduce
the bending energy.

A Type II superconducting foil will deal with
lowering the bending energy in a different way. Above the
first critical magnetic field, Hc1, the material allows
magnetic fields to penetrate, while trying to minimize the
total energy of the system. A Type II superconducting
material wants to have as much boundary between normal
regions, with field lines going through them, and the
superconducting regions because the energy is lowered if
it can maximize the length of the superconducting/normal
boundaries. In order to do this and also minimize the
bending energy, the magnetic field lines are broken up into
many tiny regions that are all evenly spaced. Each tiny
region contains a single unit of magnetic field, a flux
quantum, or flux vortex. Just as electric charge is quantized
to the charge of an electron, the magnetic field is quantized
to a flux quantum. As the applied magnetic field is
increased, the density of the flux quanta increases. The
flux quanta interact with one another. As they try to move
as far apart from one another as they can, they form a
triangular lattice pattern.

These patterns can be studied by the Bitter technique.
A metal foil is cooled with the magnetic field applied in a
small gas filled container and then a small amount of iron
is very carefully vapourized. The iron particles drift like
cigarette smoke and fall onto the foil. The local magnetic
field affects how the iron collects on the surface. The iron
prefers to go to the higher magnetic field areas. By
warming up the foil and either looking at it with an optical
microscope or, for very high resolution, with a scanning
electron microscope, the original field distributions can
be seen. Figure 1. shows several images of the vortex
lattices (Abrikosov lattices) running through a Type II
superconductor, YBa2Cu3O7. Figure 2. is an image of a
Type I superconductor which was field-cooled and
decorated with iron. Here you do not see the individual
flux quanta running through the superconductor but instead
see relatively large domains of either superconductor (no
field penetration, therefore no iron build-up) and normal
conductor (field penetrates and iron collects).

Superconducting wires can be extremely useful for
making electromagnets. Because the wire has no electric
resistance, no power is required to maintain the magnetic
field. To be practical, the wire is desired to have a high
critical temperature, as it will be less expensive to keep
cold. The higher the Tc the better, but in fact certain values
of temperatures are very significant. Liquid helium, which
has a temperature of 4.2K, can be easily stored in efficient
storage dewars (thermos'). Useful superconducting magnet
wires should then have a Tc higher than 4.2K.

Another issue is that the superconductor is influenced
by the size of the magnetic field. As the magnetic
field increases, the superconductor's Tc decreases. The
rate of decrease of Tc in magnetic field depends on the
superconducting material. The best magnet wires are type
II superconductors, and so flux lines penetrate the wire and
produce vortices. As the field is increased the density of
the vortices increases and the superconducting regions
decrease. Superconducting materials have a critical current
density above which they stop superconducting. As
the field is increased, the current density increases for a
given total current because of the increase in normal
conducting regions. A failure mode for superconducting
wires is that although there is no electrical resistance due
to the electrons colliding with defects or the material’s
ion lattice, resistance can arise from flux lines moving
around. To avoid this resistance, the flux lines must be
pinned into energy wells. This is done by purposely
introducing defects in the superconductor in anticipation
for flux lines to get pinned. Not every flux line has to be
pinned because they interact with each other to produce
the vortex lattice. If many of the vortices are pinned, they
can hold down the whole vortex lattice from moving and
dissipating energy and producing a finite resistance.
Another problem with superconducting magnet wire
is that superconductors do not conduct heat very well.
Electrons are usually the most significant contributor to
thermal conductivity The conduction electrons in a normal
metal act as a gas running through the ionic lattice,
bouncing against the lattice and transferring energy. This
electron cooling is similar to air cooling or heating an
object by blowing on it. Due to the nature of the superconducting
state, the superconducting electrons do not collide
with the ionic lattice, do not produce electrical resistance,
and also do not transfer their heat energy and provide
thermal conductivity. This is a problem because if any part
of the magnet wire goes normal, a lot of energy is dumped
into a very small area. If the heat energy is not conducted
away quickly, there is enough energy to melt the wires and
destroy the magnet. To improve the thermal conductivity
of the magnet wires, the strands of superconducting wire
are imbedded in copper, an excellent thermal conductor.
Figure 3 shows a cross sectional view of a superconducting
wire.
Image
You can see small (about 1um diameter) superconducting
fibers, surrounded by a thin diffusion barrier,
which are then imbedded in copper. The diffusion barrier
is extremely important to avoid the Sn reacting with the
copper. Parameters have to be optimized to have the
proper amount of thermal conductivity (copper), protection
from diffusion (diffusion barrier thickness) and current
capacity (superconducting wires).

Magnetic flux can be measured in a very sensitive
way with a Superconducting Quantum Interference Device
(SQUID). In short, the basic element of a SQUID is a
superconducting metal ring into which one or more
Josephson junctions (ie. weak links) are integrated. Current
is applied to two leads attached to the ring and the magnetic
flux that the ring contains induces a voltage change. In this
way, as little as 10-10 gauss of flux can easily be measured
(the earth’s field is ½ gauss and the strongest magnets are
on the order of 105 gauss). The SQUID’s extreme sensitivity
consequently makes it an attractive device for a wide range
of applications in which one desires to quantify small
physical quantities that are associated with magnetic flux.
Specific examples include current, voltage, movement
and of course magnetic fields and their gradients. The
resolution of such measurements is only limited by so
called ‘1/f noise’ (a type of ‘flicker’ noise that varies
reciprocally with frequency) caused by the thermally
activated hopping of the flux vortices between pinning
sites in the superconducting films. A significant research
effort is presently being made to better understand and
reduce 1/f noise in order to make more sensitive amplifiers
and sensors. The noise levels have nearly entered the
quantum limit due to the Heisenberg uncertainty principle.
With superconducting devices running in the quantum
noise limited regime, new ways of implementing these
devices and applications such as quantum computers will
be feasible.
http://www.physics.uwaterloo.ca/p13news/pdfs/107.pdf
The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.
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