this documents explains the clear view of superconductor applications.

1. Applications of Super conductors
Santhosh Kumar. S, Venkatesh. S,
Karpagam institute of technology,
Coimbatore.
Abstract:
As a consequence, the past decade or two of superconductor discovery can best be
summarized by the phrase “expect the unexpected”. Superconductivity is an electrical
resistance of exactly zero which occurs in certain materials below a characteristic
temperature. It was discovered by Heike Kamerlingh Onnes in 1911. Like ferromagnetism
and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. The
behavior of superconductor suggests that electron pairs are coupling over a range of hundreds
of nanometers, three orders of magnitude larger than the lattice spacing, called cooper pairs.
These coupled electrons can take the character of a boson and condense into the ground state.
This clear explanation is given by BCS theory. hereby after reading this paper you will easily
get the clear ideas of Josephson Devices-BCS theory-applications such as super conducting
generators, SEMS, superconducting cables.

2. Introduction: 1. London theory- 1935:
Kamerlingh onnes, founder of This is the first macroscopic theory
super conductivity observed that mercury to explain the concept of super
acts as superconductor below 4.2 k conductivity London proposed that there
temperature. The resistance of his mercury are two types of conduction electron
sample did not tend toward some constants namely super electrons, normal electrons.
value as the temperature was reduced Here, the super electrons are not subjected
below 4.2k. At 4.15k, the DC resistance of to any lattice scattering and they move
the sample is completely vanished. freely over the lattices points. But the total
conduction electron density is equal to
In 1913, he wrote that no doubt sum of super electrons and normal
was left of the existence of a new state of electrons.
mercury in its resistance has practically
vanished superconducting state. 2. Ginsburg- Landau Theory-1950:
The most striking and well known This theory gives the idea that the
property of superconductor is their lack of super conducting state is characterized by
electrical resistance. In 1933, Meissner and a single complex wave function. This
Ochsen field found, most surprisingly, that theory describes the properties of super
when a pure metal is cooled through its conducting state such as meissner effect,
superconducting transition temperature in zero electrical resistance and Type II super
the presence of magnetic field all magnetic conductor.
flux is expelled from within its bulk.
Spontaneous exclusion of magnetic flux 3. Bardeen, Cooper and Schrieffer
from a superconductor could not be quite (BCS) theory:
complete of course, even in principle This is the first microscopic theory
currents in metals arises from the flow of based on quantum theory. They introduced
electrons and no physical current sheet can a new pair of electrons called cooper pair
be made indefinitely thin due to repulsion and they are responsible for the super
force between these electrons. Hence the conductivity.
temperature at which a normal conductor
loses its resistivity and become a Principle:
superconductor is known as transition
temperature (or) critical temperature. This theory states that the electrons
experience a special type of attractive
At the transition temperature, the interaction, overcoming the coulomb
following physical changes are observed. forces of repulsion between them, as a
result Cooper pairs (i.e.,) electrons pairs
1. The electrical resistance drops to are formed. At low temperature these
zero. pair’s moves without scattering (i.e.,)
2. The magnetic flux lines are without any resistance through the lattice
excluded from the material. points and the material becomes
3. There is a discontinuous change in superconductor. Here the electrons- lattice-
specific heat. electrons interaction should be stronger
4. Further there are also a small than electron-electron interaction.
change in thermal conductivity and
the volume of the material. The superconducting state of a
metal may be considered to be resulting
With the help of reference given by from cooperative behavior of conduction
onnes, the succeeding scholars proposed electrons. Such a cooperation or coherence
the following theories.

3. of electrons takes place when a number of
electrons occupy the same question state.
This, however, appears to be impossible
for both statistical and dynamic reasons.
The electrons attract each other in a
certain energy range and forms pairs. A
pair of electron behaves like a boson. Thus
a number of pairs can occupy the same
quantum state which causes coherence
among electrons. In the electron – lattice - electron
interaction, the electron will not be fixed,
When an electron they move in opposite direction and their
moves through a crystal, it produces lattice co-relation may persists over lengths of
distortion and sets the heavier ions into maximum 10-6 m. this length is called
slow forced oscillations. Since the electron coherence length.
moves very fast it leaves this region much
Temperature:
before the oscillations can die off.
Meanwhile, if another electron happens to When the temperature (T) is less
pass to pass through this distorted region, than the critical temperature (Tc), the
it experiences a force which is one of resistivity due to lattice vibrations will be
less. If the electron – lattice- electron is
attraction and is of the type of polarization
stronger than electron-electron interaction
force. This attractive force lowers the than more number of cooper pairs
energy of the second electron. The electrons will be generated, these cooper
repulsive force between the electrons is pairs electrons will sail (move freely) over
small since the Coulomb’s repulsion is the lattice points without any exchange in
instantaneous while the attraction energy. So, they will not be slowed down.
meditated by lattice distortion is highly Hence, the material property and the
conductivity becomes infinite and
regarded in time. Therefore, the attraction
exhibiting the phenomenon of as super
caused by even a weak lattice distortion conductivity.
can overcome stranger Coulomb’s
repulsion. Thus the net effect is the General properties of super conductors:
attraction of two electrons via lattice
1. Electrical resistance
distortion to form a pair of electrons
known as the cooper pair. It is now The electrical resistivity drops to zero
obvious that the mass of an ion has an at the transition temperature. One can
important role conclude that super conductors have
virtually zero Electrical resistance and they
Cooper pairs:
can conduct Electricity without resistance.
The pairs of electrons formed due
2. Diamagnetic property
to electron – lattice- electron interaction
(forces of attraction) by overcoming the The super conductors are a perfect
electron-electron interaction (forces of
diamagnetic. As the material which is
repulsion) with equal and opposite
momentum spins called Cooper Pairs. placed in a uniform magnetic field (whose
value is smaller than the critical magnetic

4. Hc), is cooled below Tc” the magnetic flux Correspondingly. The value of the
inside material is excluded from the field will be different for different
material. This is called Meissner effect.
materials.
Thus a material can behave as a 4. Effect of magnetic current:
superconductors only when
The superconducting properties of
I. The resistivity of the material conductors disappear when a
should be zero and
sufficiently heavy current is passed
II. The magnetic induction in the
material should be zero when it is though them.
placed in an uniform magnetic Since when current flows through
field.
conductor it will set up
Both the conditions are
The magnetic field which destroys the
independent to each other and to
super conducting state. According to
get super conducting state, these
Silsbee’s rule, for a superconducting
two conditions should
wire.
simultaneously exist in the
IC =2π r HC
material.
Where IC is the critical
current and r is the radius of the wire.
3. Effect of magnetic field
5. Effect of pressure
Below TC, Superconducting can
By applying very high pressure,
be destroyed by the application of
we can bring TC of a material nearer to
strong magnetic field. At the
room temperature .if we increase the
temperature, the minimum field
pressure on the material, Tc also
required to destroy superconductivity
increases. TC is directly proportional
is called critical field (Hc) of the
to pressure at very pressures.
material. Thus the value of the critical
Researchers are going on to get
field depends upon the temperature of
superconducting state at room
the super conducting material.
temperature by applying very high
HC=Ho {1-(T2 /Tc2)}
pressures.
Where Ho =critical field 0 K.
6. Isotope effect
Maxwell found that the transition
One can know that when the
temperatures are inversely proportional
temperature of the material increases,
to the square roots of the atomic
the value of the critical magnetic field
weights of the isotopes of a single
decreases
superconductor .thus,

5. Mα Tc = a constant Then we learn something about Josephson
Where α is a constant and it is devices,
approximately equal to 0.5 .for The Josephson effects and tunneling:
example the atomic weights of isotopes Josephson observered some remarkable
of mercury are from 199.5 to 203.4 effects associated with the tunneling of
atomic mass units . Therefore their super conducting electrons through a very
thin insulator (1-5nm) sandwiched
transition temperatures are also from
between two superconductors. Such an
4.185k to 4.146k respectively. insulating layer forms a weak link between
the super conductors which is referred to
Other general properties: as the Josephson junction. The effects
observed are given below
1. Generally good conductors are not good
super conductors. Example: gold (i) The DC Josephson effect
According to this effect, a dc
2. The critical temperature and the critical
magnetic field of a current flow across the
superconductor changes slightly under the junction, even when there is no
influence of an applied
voltage is applied across it.
stress. A stress increases the dimensions of
the specimen increases (ii) The AC Josephson effect
the transition temperature and produces a If a dc voltage is applied across
corresponding changes in the critical the junction, rf current of
magnetic field.
oscillations of frequency
3. The introduction of chemical impurities
modifies almost all the f=2eV/h are step across it. By
superconducting properties particularly the measuring the frequency and
magnetic ones. voltage, the value of e/h can be
4. The elastic properties and the thermal
determined. Hence this effect
expansion coefficient remain
unaffected below and above Tc. has been utilized to measure e/h
5. The superconducting state does not very precisely and may be used
exhibit any thermoelectric effect.
as a means of establishing a
6. No changes in photo electric properties
are observed. voltage standard. Furthermore,
7. No appreciable changes in the an application of rf voltage
reflectivity are observed in the
along with the dc voltage can
visible and infrared regions.
result in flow of direct current
8. The zero resistance of superconductors
through the junction.
changes slightly at very
high frequencies (above 10 MHz) of the (iii) Macroscopic quantum
alternative current. interference

6. This effect explains the sensitive to very small changes
influence of the applied in magnetic field, the SQUID
magnetic field on the super can be used as galvanometer.
current flowing through the The flow of current takes place
junction. According to this between any two points where
junction =n if dc magnetic field the wave function has different
is applied to superconducting phases. The changes in phases
circuit containing two can also be brought about by
junctions, the maximum super the applied electric and
current shows interference magnetic fields. The states
effect which depend on the having different phases can be
intensity of magnetic field. super imposed by using the
Consider the arrangement as arrangement. Thus the
show in the fig. which is Josephson effects exhibit the
known as the super conducting quantum interference
quantum interference device phenomenon on macroscopic
(SQUIDS). It consists of ring scale. The interference depends
of superconducting material on the phase of the state which
having two side arms A and B can be changed by applying
which act as entrance and exit electric and magnetic fields,
of super current respectively. and the states with different
The insulating layers P and Q phases can produce interference
may, in general they have effects.
different thickness and currents
Let us discuss about the new applications
through the layers are I1 and I2 of super conductivity
respectively. This variation of
What is a superconducting Generator?
I1 and I2 versus the magnetic A common generator converts rotational
field as obtained. Both I1 and I2 mechanical input energy, such as that from
vary periodically with the a steam or gas turbine, into electricity. It
does this by rotating a rotor field, which
magnetic field, the periodicity
produces voltage in stationary armature
of I1 being greater than that of conductors. The generator field can be
I2. The variation of I2 is the produced with copper windings or
permanent magnets. In large machines,
interference effect of the two
mechanical considerations and the desire
junctions. Since the current is

7. to vary the level of field produced HTS generators will produce electric
typically favour the use of copper power with lower losses than their
windings over permanent magnets. The conventional equivalents. A 1,000 MW
superconducting generator (a typical size
difference between the basic design of a
in large power plants) could save as much
conventional and as $4 million per year in reduced losses
superconducting generator will be better per generator. Even small efficiency
appreciated in the light of improvements produce big dollar savings.
the fundamentals of generation. A half of one percent improvement
In the generator, mechanical energy is provides a utility or IPP with additional
converted into electrical capacity to sell with a related value of
nearly $300,000 per 100 MVA generator.
energy by rotating a conductor relative to
The worldwide demand for additional
magnetic field produced electrical generation is ever increasing.
usually by an electromagnet. The resulting The National Energy Information Center
flow of current in forecasts that the world will require
conductor generates its own magnetic 500,000 MW of additional electric
field. The final useful generating capacity over the next ten
electrical output depends upon the years.
interaction of these two magnetic fields.
Superconducting magnetic energy
Benefits of superconducting generators: storage system (SEMS):
 50% reduction in size and weight. This CTW description focuses on
Superconducting Magnetic Energy Storage
 70% less in transportation cost.
(SMES). This technology is based on three
 Cheaper foundation and buildings.
concepts that do not apply to other energy
 1% higher electrical efficiency. storage technologies. First, some materials
carry current with no resistive losses.
 Higher stability due to lower
machine reactance. Second, electric currents produce magnetic
fields. Third, magnetic fields are a form of
Efficient gain of superconducting
pure energy which can be stored.
generators:
Generators lose power in the rotor SMES combines these three fundamental
windings and in the armature bars. By principles to efficiently store energy in a
using superconducting wire for the field superconducting coil. SMES was
windings, these losses can be practically originally proposed for large-scale, load
eliminated. The fields created in the leveling, but, because of its rapid
armature by the rotor are not limited by the
discharge capabilities, it has been
saturation characteristics of iron and the
armatures are constructed without iron implemented on electric power systems for
teeth. This removes the losses experienced pulsed-power and system stability
in the armature teeth. The added space for applications. Operationally, SMES is
copper in the armature made possible by different from other storage technologies
the removal of the armature teeth further in that a continuously circulating current
reduces losses.

8. within the superconducting coil produces reducing the storage time would increase
the stored energy. In addition, the only the economic viability of the technology.
conversion process in the SMES system is Thus, there has also been considerable
from AC to DC. As a result, there are none development on SMES for pulsed power
of the inherent thermodynamic losses systems.
associated with conversion of one type of Power Conversion System
energy to another. The combination Charging and discharging a SMES coil is
of the three fundamental principles different from that of other storage
(current with no restrictive losses; technologies. The coil carries a current at
magnetic fields; and energy storage in a any state of charge. Since the current
magnetic field) provides the potential for always flows in one direction, the power
the highly efficient storage of electrical conversion system (PCS) must produce a
energy in a superconducting coil. positive voltage across the coil when
Operationally, SMES is different from energy is to be stored, which causes the
other storage technologies in that a current to increase. Similarly, for
continuously circulating current within the discharge, the electronics in the PCS are
superconducting coil produces the stored adjusted to make it appear as a load across
energy. In addition, the only conversion the coil. This produces a negative voltage
process in the SMES system is from AC to causing the coil to discharge. The product
DC. As a result, there are none of the of this applied voltage and the
inherent thermodynamic losses associated instantaneous current determine the power.
with conversion of one type of energy to SMES manufacturers design their systems
another (EPRI, 2002).The original so that both the coil current and the
development of SMES systems was for allowable voltage include safety and
load levelling as an alternative to pumped performance margins. Thus, the PCS
hydroelectric storage. Thus, large energy power capacity typically determines the
storage systems were considered initially. rated capacity of the SMES unit (EPRI,
Research and then significant development 2002). The PCS provides an interface
were carried out over a quarter century, between the stored energy (related to the
beginning in the early 1970s. In the U.S., direct current in the coil) and the AC in the
this effort was mainly supported by the power grid.
Department of Defense, the Department of Control System
Energy, and Electric Power Research The control system establishes a link
Institute (EPRI). Internationally, Japan had between power demands from the grid and
a significant program for about 20 years, power flow to and from the SMES coil. It
and several European countries receives dispatch signals from the power
participated at a modest level. grid and status information from the
At several points during the SMES SMES coil. The integration of the dispatch
development process, researchers request and charge level determines the
recognized that the rapid discharge response of the SMES unit. The control
potential of SMES, together with the system also measures the condition of the
relatively high energy related (coil) costs SMES coil, the refrigerator, and other
for bulk storage, made smaller systems equipment. It maintains system safety and
more attractive and that significantly sends system status information to the

9. operator. Modern SMES systems are tied perfectly efficient, so there is some loss of
to the Internet to provide remote liquid nitrogen needed to cool the line.
observation and control. Typical values for cooling efficiency are
estimated to be on the order of 10% [3].
Super conducting transmission line Furthermore, there are losses due to the
cables: imperfect efficiency of the liquid nitrogen
The obvious advantage of superconducting pumping system itself, as well as hydraulic
transmission lines is they have no resistive losses due to the flow friction in the
losses in the bulk. If superconducting circulating liquid nitrogen.
transmission lines had no other sources of Similar to conventional transmission lines,
power dissipation, the choice between superconducting transmission lines also
types of transmission lines would be easy. have shield and dielectric losses, which
We would simply calculate the cost of can be calculated using the same physical
conventional power lines and subtract the models. Unlike conventional lines,
cost of the power that is dissipated in superconducting transmission lines have
transporting the electricity. Then, we conductor AC losses. There is no generally
would compare it to the cost of making accepted physical model to describe these
and cooling superconducting transmission losses; so much of the data is empirical.
lines. There are also losses due to imperfect
Of course, real superconducting cables thermal insulation of the superconducting
have other sources of loss which must also cable. The result is a thermal leak between
be factored in. There are a number of the cold liquid nitrogen and the warm
major sources of losses in superconducting surroundings. The losses can be reduced
transmission lines, many of them but not eliminated by creating a vacuum
fundamentally different from those in between the superconducting cable and the
conventional transmission lines. There are thermal insulator. Finally, there are small
a number of relatively small losses due to losses due to joints and terminations of
need to cool the line. No cooling system is cables.
Conclusion:
Superconductors are always amazing in this world. Developed and developing countries of
our world are constantly thinking about this super power. Production and transmission of
electricity should be improved still more to conserve for future generation. Scientists are
working on designing superconductors that can operate at room temperature. In Tamil Nadu
we suffer from frequent shut downs. In spite of using nuclear reactor in our country, which
cause fear to our people, our Indian researchers and scholars can take part in this wondering
super conducting power?