1. UNIT-IV MAGNETIC AND SUPER CONDUCTING PROPERTIES

2. MAGNETIC PROPERTIES

3. HISTORICAL BACKGROUND
Magnets have been known for Centuries. The Chinese and Greeks knew about the “magical” properties of magnets.
The ancient Greeks used a stone substance called “magnetite” a natural magnetic material Fe3O4. They discovered that the stone always pointed towards north.
Later, stones of magnetite called “lodestones” were used in navigation.
Term magnet comes from the ancient Greek city of Magnesia, at which many natural magnets were found.

4. Pliny (23-79 AD Roman) wrote of a hill near the river Indus that was made entirely of a stone that attracted iron.
Chinese as early as 121 AD knew that an iron rod which had been brought near one of these natural magnets would acquire and retain the magnetic property. when this rod is suspended from a string it would align itself in a north-south direction.
Use of magnets to aid in navigation can be traced back to at least the eleventh century.
William Gilbert, an English physician, first proposed in 1600 that the earth itself is a magnet, and he predicted that the Earth would be found to have magnetic posles.

5. A large electromagnet used to lift scrap metal
Magnetism:
Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.
A large electromagnet used to lift scrap metal

6. MAGNETIC DIPOLE:
The ends of a magnet are where the magnetic effect is the strongest. These are called “poles.” Each magnet has 2 poles – 1 north, 1 south.
Any two opposite poles separated by a finite distance constitute a magnetic dipole.

7. For Every North, There is a South
No Monopoles Allowed S N

8. Like pole repels!
Opposite poles attract!

9. Magnetic dipole moment or magnetic moment (μm):
It is defined as the product of pole strengh (m) and the distance between dipoles (2l).
Magnetic moment due to a current (I) carrying circular wire of area of cross-section (A).
UNITS: Am2

10. THE CONCEPT OF “FIELDS”
Magnetic field:
The space surrounding the magnet upto which its influence felt is known as magnetic field.
Michael Faraday

11. MAGNETIZATION:
It is a measure of how a material respond when magnetic field is applied to it.
INTENSITY OF MAGNETIZATION (M):
When a material is magnetized, it develops a net magnetic moment. The magnetic moment per unit volume is called intensity of magnetization.
Units: Am-1

12. MAGNETIC FLUX (Φ):
Magnetic flux is the product of the average magnetic field times the perpendicular area that it penetrates.
The contribution to magnetic flux for a given area is equal to the area times the component of magnetic field perpendicular to the area.
For a closed surface, the sum of magnetic flux is always equal to zero (Gauss' law for magnetism).
No matter how small the volume, the magnetic sources are always dipole sources (like miniature bar magnets), so that there are as many magnetic field lines coming in (to the south pole) as out (from the north pole).

13. Magnetic Induction or magnetic flux density (B)
It is defined as the number of lines of force passing through the unit area perpendicularly.
Units: Wb/m2 or tesla

14. This the characteristic property of a medium.
Permeability (μ)
This the characteristic property of a medium.
It indicates the ease with which the material allows the magnetic lines of force to pass through it. OR
It is the measure of the ability of a material to support the formation of a magnetic field within itself.
In other words, it is the degree of magnetization that a material obtains in response to an applied magnetic field.
μr- relative permeability of the medium
μ0 – permeability of free space or perme 4π×10−7 H.m-1
SI UNITS: Henry per meter(H.m-1), Newton per Ampere square (N.A-2)

15. Magnetic field intensity (H)
Magnetic field intensity at any point in the magnetic field is the force experienced by an unit north pole placed at that point.
Magnetic susceptibility ( ):
 Magnetic susceptibility is the degree of magnetization of a material in response to an applied magnetic field.
Where
M is magnetization,
H is magnetic field intensity
The proportionality constant is called susceptibility. Its value may be zero, positive or negative.

16. The magnetic induction and magnetic field intensity are related by
In vacuum
, Since M=0
In a medium
Since,
where
Relative permeability

17. Conversion between CGS and SI magnetic units.
Quantity
 Symbol
SI Units (Sommerfeld)
SI Units (Kennelly)
CGS Units (Gaussian)
Field H
A/m
Oersteds
Flux Density (Magnetic Induction) B
Tesla
Gauss
Flux f
Weber
Maxwell
Magnetization M -
erg/Oe-cm3
Conversion between CGS and SI magnetic units.

18. Origin of magnetic moment
Orbital Motion - Orbital magnetic moment
Spin motion – Spin magnetic moment

19. - I μorb Orbital magnetic moment
The revolving electron in circular orbit establishes a current given by
I= charge/time period= -e/(2π/ω)= - ωe/2 π
The current establishes a magnetic field around the circular orbit, so that upper surface act as South pole and lower surface acts as North pole.
Then orbital magnetic moment is given by
Angular momentum = linear momentum x radius
=mvr
=mωr2 - I
μorb

20. Angular momentum associated with orbital quantum number l is
is the fundamental unit of magnetic moment known as Bohr magneton and its value is 9.27 x A/m2

21. - I μs Spin magnetic moment
Where, g is dimensionless number and is called g-factor.
This number depends upon the particle. For electron its value is ~2 μs - I

22. An atom is said to be magnet if it carries a permanent dipole moment.
Every substance is formed from an assembly of atoms which can be either non-magnetic or magnetic.
The magnetic materials are classified into five groups depending on their response to the magnetic field.
Diamagnetic Materials
Paramagnetic Materials
Ferromagnetic Materials
Antiferromagnetic Materials
Ferrimagnetic Materials

23. DIAMAGNETISM
Diamagnetism characterizes the substances that have only non- magnetic atoms (lack of permanent diople moment).
Origin:
An electron moving around the nucleus results in magnetic moment.
Due to different orientations of various orbits of an atom, the net magnetic moment is zero in diamagnetic materials.
When an external field is applied the motion of electrons in their orbits changes resulting in induced magnetic moment in a direction opposite to the direction of applied field.

24. The magnetization induced by the applied magnetic field is very weak and the magnetic lines of force are repelled.
This magnetism is also exist in substances with magnetic atoms, but very weak and completely masked by the contribution of magnetic atoms.
Relative permeability is slightly less than unity.
The magnetic susceptibility is independent of applied magnetic field strength.

25. Magnitude of susceptibility Temperature dependence
Examples
Small & negative
Independent
Organic materials, light elements
Intermediate & negative
Below 20K varies with field and temperature
Alkali earhs, Bismuth
Large & Negative
Exists only below critical temperature (Meissner effect)
Superconducting materials

26. PARAMAGNETISM
The paramagnetic substances consists of magnetic atom that posses permanent dipole moment
Origin
Each electron in an orbit has an orbital magnetic moment and a spin magnetic moment.
When the shells are unfilled there is net magnetic moment.
In the absence of the external field the net moments of the atoms are arranged in random directions because of thermal fluctuations. Hence there is no magnetization.
When external magnetic field is applied, there is tendency for the dipoles to align with the field giving rise to an induced positive dipole moment.
The induced magnetism is the source for paramagnetic behaviour.

27. Magnitude of susceptibility Temperature dependence
Paramagnetic susceptibility is small and positive and is independent of applied field strength.
Spin alignment is random.
Magnitude of susceptibility
Temperature dependence
Examples
Small & positive
Independent
Alkali metals, transition metals, rare earths
Large & positive
Curie law
Curie-Weiss law

28. FERROMAGNETISM
Even in the absence of external applied field, some substances exhibits strong magnetization.
This is due to a special form of interaction called exchange coupling between adjacent atoms that results in spontaneous magnetization of the substance.
When placed inside a magnetic field, it attracts the magnetic lines of force very strongly.
Each ferromagnetic material has a characteristic temperature called the ferromagnetic Curie temperature θf. Below this temperature the spontaneous magnetization exists.

29. Magnitude of susceptibility Temperature dependence
Spin alignment is parallel.
Ferromagnetic materials exhibit Hysteresis.
They Consists of a number of small regions which are called domains.
Magnitude of susceptibility
Temperature dependence
Examples
Very large & positive
For T>θf paramagnetic behavior
For T<θf ferromagnetic behavior
Fe, Co, Ni, Gd

31. ANTI-FERROMAGNETISM
Antiferromagnetism macroscopically similar to paramagnetism, is a weak form of magnetism.
In certain materials when the distance between the interacting atoms is small the exchange forces produce a tendency for antiparallel alignment of electron spins of neighboring atoms.
The magnetic susceptibility increase with the increase of temperature and reaches maximum at a certain temperature. This temperature is known as Neel temperature (TN). Above this temperature the susceptibility again decreases.

32. Magnitude of susceptibility Temperature dependence
Spins are aligned antiparallel
Magnitude of susceptibility
Temperature dependence
Examples
small & positive
when T>TN
when T<TN
Salts of transition metals

33. FERRIMAGNETISM This is a special case of antiferromagnetism.
The net magnetization of magnetic sublattices is not zero, since antiparallel moments are of different magnitudes.
Hence ferrimagnetic materials possesses a net magnetic moment.
This moment disappears above a Curie temperature analogous to the Neel temperature.
Above TC, thermal energy randomizes the individual magnetic moments and the material becomes paramagnetic.

34. Magnitude of susceptibility Temperature dependence
Ferrimagnetic domains become magnetic bubbles to act as memory elements.
Spin alignment is antiparallel of different magnitudes.
Magnitude of susceptibility
Temperature dependence
Examples
Very large & positive
when T>TN
when T<TN behaves as paramagnetic material
Ferrites

35. HYSTERESIS
Hysteresis of ferromagnetic materials refers to the lag of magnetization behind the magnetizing field.
A hysteresis loop is a curve showing the change in magnetic induction of a ferromagnetic material with an external field.
When the external magnetic field is increased the magnetic induction increases.

36. Once magnetic saturation has been achieved, a decrease in the applied field back to zero results in a macroscopically permanent or residual magnetization, known as remanance, Mr. The corresponding induction, Br, is called retentivity or remanent induction of the magnetic material. This effect of retardation by material is called hysteresis.
The magnetic field strength needed to bring the induced magnetization to zero is termed as coercivity, Hc. This must be applied anti-parallel to the original field.
A further increase in the field in the opposite direction results in a maximum induction in the opposite direction. The field can once again be reversed, and the field-magnetization loop can be closed, this loop is known as hysteresis loop or B-H plot or M- H plot.

37. Below the ferromagnetic Curie temperature ferromagnetic substances exhibit hysteresis.
The phenomenon of hysteresis can be explained with domain theory.
A region in a ferromagnetic material where all the magnetic moments are aligned in the same direction is called a domain.
Each of these domains is separated from the rest by domain boundaries / domain walls.
Boundaries, also called Bloch walls, are narrow zones in which the direction of the magnetic moment gradually and continuously changes from one domain to that of the next.

38. 1. The motion of domain walls 2. Rotation of domains
Block wall transition (B) between domains (A) and (C) with 180° difference
The increase in the value of the resultant magnetic moment of the specimen under the action of the applied field can be attributed to
1. The motion of domain walls
2. Rotation of domains

39. Reversible wall displacement irreversible wall displacement
When a weak magnetic field is applied, the domains that are aligned parallel to the field and in easy direction of magnetization grow in size at the expense of less favorably oriented ones. This results in the Bloch wall movement.
When the weak field is removed the domains reverse back to their original state. Shown by the curve OA. O A
Reversible wall displacement
irreversible wall displacement
Domain rotation B

40. When the field becomes stronger the Bloch wall movement continues and it is mostly irreversible movement. Shown by the curve AB.
At the point B all domains have got magnetized along their easy directions.
Field is further increased the domains rotate in the field direction which is away from the easy direction thereby storing anisotropy energy.
Once the domain rotation is complete the specimen is saturated.
On the removal of the field the specimen tend to attain the original configuration by the movement of Bloch walls. But this movement is hampered by impurities, lattice imperfections etc.

41. A Coercive field is required to reduce the magnetization of the specimen to zero.
The amount of energy spent in this regard is a loss.
Hysteresis loss is the loss of energy in taking a ferromagnetic body through a complete cycle of magnetization and this loss is represented by the area enclosed by the hysteresis loop.

42. Hard magnets soft magnets
Based on the area of the hysteresis loop the magnetic materials are classified into two types
1. Hard magnetic materials
2. Soft magnetic materials
Hard magnets
soft magnets

43. Hard magnets These are also called permanent magnets or hard magnets.
Hard magnets are characterized by high remanent inductions and high coercivities.
These are also called permanent magnets or hard magnets.
These are found useful in many applications including fractional horse-power motors, automobiles, audio- and video- recorders, earphones, computer peripherals, and clocks.
They generally exhibit large hysteresis losses.
Ex.: Co-steel, Tungsten steel, SmCo5, Nd2Fe14B, ferrite Bao.6Fe2O3, CuNiFe (60% Cu 20% Ni-20% Fe), Alnico (alloy of Al, Ni, Co and Fe), etc.

44. SOFT MAGNETS
Soft magnets are characterized by low coercive forces and high magnetic permeabilities; and are easily magnetized and de- magnetized.
They generally exhibit small hysteresis losses.
Application of soft magnets include: cores for electro-magnets, electric motors, transformers, generators, and other electrical equipment.
Ex.: ingot iron, low-carbon steel, Silicon iron, superalloy (80% Ni-5% Mo-Fe), 45 Permalloy (55%Fe-45%Ni), 2-79 Permalloy (79% Ni-4% Mo-Fe), MnZn ferrite / Ferroxcube A (48% MnFe2O4- 52%ZnFe2O4), NiZn ferrite / Ferroxcube B (36% NiFe2O4-64% ZnFe2O4), etc.

45. Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles or domains, each of which stores one bit of data.

46. SUPERCONDUCTIVITY

47. Definitions
Tc: This is the critical temperature at which the resistivity of a superconductor goes to zero. Above this temperature the material is non-superconducting, while below it, the material becomes superconducting.
Bc: The scientific notation representing the "critical field" or maximum magnetic field that a superconductor can endure before it is "quenched" and returns to a non-superconducting state. Usually a higher Tc also brings a higher Bc. Type II superconductors have lower Bc1 and upper Bc2 critical fields.

48. INTRODUCTION
For some materials, the resistivity vanishes at some low temperature: they become superconducting.
Superconductivity is the ability of certain materials to conduct electrical current with no resistance. Thus, superconductors can carry large amounts of current with little or no loss of energy
In July 1909, Heike Kamerlingh Onnes found that the resistance of mercury dropped suddenly to an immeasurable small value when it is cooled below 4.2K. Onnes termed the new electrical state that the mercury had entered the superconducting state.

49. PROPERTIES VIS-A-VIS SUPERCONDUCTIVITY
Properties not affected :
Elastic properties
Thermal expansion behaviour
Photoelectric properties
Internal arrangement of crystal lattice as confirmed by X-ray diffraction pattern before and after such a transition
Properties affected :
Magnetic properties change
Electrical properties : as the electrical resistivity tendo to zero at T=Tc
All thermo electric effects disappear for T  Tc
Specific heat shows a discontinuous change
Some latent heat of transition may also be involved
The transition in zero magnetic field from the superconducting state to the nornal state is not exactly involving latent heat , though there is discontinuity in the heat capacity – temp2 graph
Entropy shows a decrease for T  Tc

50. NON SUPERCONDUCTOR
SUPERCONDUCTOR
Bint = 0
Bint = Bext

51. MESSINER EFFECT
MEISSNER EFFECT : Meissner and Ochsenfeld discovered that when a superconductor is cooled in a magnetic field to below the value of transition temperature corresponding to that field, then the lines of magnetic induction B are pushed out of the bulk superconductor.

52. TYPE I SUPERCONDUCTORS
Type I superconductors : These are superconductors which exhibit
Complete Meissner effect.
There are 30 pure metals which exhibit zero resistivity at
low temperature.
They are called Type I superconductors (Soft
Superconductors).
The superconductivity exists only below their critical temperature and below a critical magnetic field strength.

53. Type I Superconductors
Mat.
Tc (K) Be Rh W
0.015 Ir
0.1 Lu Hf Ru
0.5 Os
0.7 Mo
0.92 Zr
0.546 Cd
0.56 U
0.2 Ti
0.39 Zn
0.85 Ga
1.083
Gd*
1.1 Al
1.2 Pa
1.4 Th Re Tl
2.39 In
3.408 Sn
3.722 Hg
4.153 Ta
4.47 V
5.38 La
6.00 Pb
7.193 Tc
7.77 Nb
9.46
Type I Superconductors

54. TYPE II SUPERCONDUCTORS
Type II superconductors : These are superconductors which do not exhibit Meissner effect strictly
Starting in 1930 with lead-bismuth alloys, were found which exhibited superconductivity; they are called Type II superconductors (Hard Superconductors).
They were found to have much higher critical fields and therefore could carry much higher current densities while remaining in the superconducting state.

55. Type II Superconductors

56. CHARACTERISTICS PROPERTIES OF A SUPERCONDUCTOR : FACTOR AFFECTING
Temperature : If a ring made of superconducting material is cooled in a magnetic field from ordinary temeprature to a value below its critical temperature and then the magnetic field is removed, an induced current is set up in the ring. The resistance in the superconducting state being practically zero, the decay of thie induced current will take infinitely long time.
Magnetic field : Application of magnetic field to a superconducting specimen brings a stage when for H=Hc, the critical field, the superconductor behaves like a normal material i.e., the superconductivity disappears.
Current : If the magnetic field around the superconductor is increased beyond the critical field the superconductivity is destroyed and the sample behaves as a normal material. Therefore the supercurrent will flow only up to its critical value .Once the field exceeds Hc(T) the current becomes just the ordinary current.
Stress : Application of stress increases the transition temperature. As Hc(T) is temperature dependent, increased stress is found to result in a slight change of Hc(T).
Size : Size of specimen exhibiting superconductivity is an important parameter for its behaviour.
Impurity : The presence of impurities changes almost all properties of a superconductor especially its magnetic behaviour.
Isotopic Constitution of the Specimen : The critical temperature of a specimen depends on the isotopic mass. The presence of various isotopes in a given specimen decided what its average isotope mass will be. The dependence of Tc on such a mass is also called Isotope Effect.
MaTc = constant or Tc  M-1/2

57. THERMODYNAMICAL PROPERITES OF SUPERCONDUCTING STATE
Entropy : Going from Normal state to superconducting state the entropy decreases, so the superconducting state is more ordered than the normal state.
Specific Heat : The specific heat of the normal metal obeys the relation ship, Cn(T) =  T + βT3 where as for the superconducting state the specific heat is Ces(T) = A exp (-/kβT) where A is some constant and  is superconducting energy group which is equal to one half of the minimum value of energy for destroying a cooper pair.
Energy Gap : The energy gap of superconductors is of entirely different nature than the energy gap in insulators. In superconductor the energy gap is due to electron-electron interaction in fermi gas whereas in insulator or semiconductor the energy gap is caused by electron lattice interaction. In insulators the gap prevents the flow of electrical current. Energy must be added to lift electrons from the valence band to conduction band before the current can flow. In a superconductor, on the other hand, the current flows despite the presence of energy gap . In a superconductor the electrons in the excited state above the gap behave as normal electron. The transition in zero magnetic filed from superconducting state to normal state is observed to be a second–order phase transition.

58. BCS THEORY OF SUPERCONDUCTIVITY
The microscopic theory put forward by Bradeen , Cooper and Schruffier (BCS) forms the basis of quantum theory of Superconductivity. The fundamental postulate of BCS theory is that when an attractive interaction between two electrons by means of phonon exchange dominates the repulsive coulomb interaction then the superconducting state is formed.
Electron-phonon-electron interaction : During an interaction of an electron with a positive ion of the lattice through electrostatic coulomb force, some electron momentum get transferred. As a result, these ions set up elastic wave in the lattice due to distortion. If another electron happens to pass through this region then the interaction between two occurs which in its effect lowers the energy of the second electron. The two electrons interact via the lattice distortion or the phonon field resulting in the lowering of energy of the electron which implies the force between two electrons is attractive. This interaction is strongest when two electrons have equal and opposite moments and spin and this pair is known as cooper pair.

59. COOPER PAIR
When the temperature of the specimen is lowered, if the attractive force between two electrons via a phonon exceeds coulomb repulsion between them, then a weakly bound cooper pair is formed having the binding energy of the order of 10-3 eV. The energy of Cooper pair is less than the energy of the pair in free state. The binding energy of cooper pair is called energy bang gap, Eg. When h  Eg strong absorption occurs as the cooper pairs break apart.
The electrons in cooper pair have opposite spins so the total spin of the pair is zero. As a result cooper pairs are bosons whereas electrons are fermions.

60. APPLICATIONS OF SUPERCONDUCTIVITY
Superconductors are used to make the powerful electromagnets, including those used in MRI machines, beam steering magnets used in particle accelerators.
Superconductors have also been used to make digital circuits and microwave filter for mobile phone base stations.
Promising future applications include high performance transformers, power storage devices, electric power transmission, electric motors and magnetic levitation devices.

61. Definitions
Jc: The scientific notation representing the "critical current density" or maximum current that a superconductor can carry without becoming non-superconductive.
Meissner Effect: Exhibiting diamagnetic properties to the total exclusion of all magnetic fields. (Named for Walter Meissner.) This is a classic hallmark of superconductivity and can actually be used to levitate a strong rare-earth magnet.

62. Superconductor Types Type I Type II
Exhibits perfect diamagnetism below transition temperature Tc and has only one critical magnetic field Bc.
Type II
Totally expels and excludes magnetic flux below lower critical field Bc1 and partially does so between Bc1 and upper critical field Bc2; all superconductors except elements are Type II. This type has a larger Tc than that of a Type I superconductor.

63. A Brief History of Superconductors
In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes of Leiden University. When he cooled it to the temperature of liquid helium, 4 degrees Kelvin, its resistance suddenly disappeared!
In 1933 Walter Meissner and Robert Ochsenfeld discovered that a superconducting material will repel a magnetic field. This phenomenon is known as perfect diamagnetism and is often referred to as the Meissner effect.
Since then major developments have been made in both the discovery of higher temperature superconductors as well as progress in the theory of superconductivity. In 1957 the 1st major advancement in the theory was made by American physicists John Bardeen, Leon Cooper, and John Schrieffer. Their Theories of Superconductivity became known as the BCS theory - abbreviated for the first letter of each man's last name - and won them a Nobel prize in BCS theory explained superconductivity at temperatures close to absolute zero for elements and simple alloys. However, at higher temperatures and with different superconductor systems, the BCS theory has become inadequate to fully explain how superconductivity is occurring.

64. History continued…
In 1962 Brian D. Josephson, a graduate student at Cambridge University, predicted that electrical current would flow between 2 superconducting materials - even when they are separated by a non-superconductor or insulator! His prediction that superconductors would exhibit this quantum effect on a macro scale was later confirmed and won him a share of the 1973 Nobel Prize in Physics. This tunneling phenomenon is today known as the "Josephson effect" and has been applied to electronic devices such as the SQUID (Superconducting Quantum Interference Device), an instrument capable of detecting even the weakest magnetic fields.
More recently scientists have made improvements in the area of predicting and engineering new types of superconductors. In the 80’s carbon based superconductors as well as ceramic superconductors were developed. These superconductors have fantastic magnetic properties as well as high critical temperatures, but their mechanical properties are poor.

65. Josephson effect (see also hand-out)
In 1962 Josephson predicted Cooper-pairs can tunnel through a weak link at zero voltage difference. Current in junction (called Josephson junction – Jj) is then equal to:
Electrical current flows between two SC materials - even when they are separated by a non-SC or insulator. Electrons "tunnel" through this non-SC region, and SC current flows.

66. Brian D. Josephson
The Discovery of Tunnelling Supercurrents
The Nobel Prize in Physics 1973

67. JJ’s essential in Superconducting Interference Devices
The SQUID may be configured as a magnetometer to detect incredibly small magnetic fields - small enough to measure the magnetic fields in living organisms.
Threshold for SQUID: T
Magnetic field of heart: T
Magnetic field of brain: T
Many uses in everyday life
Making measurements using SQUIDs
(magnetic susceptibility, static nuclear susceptibility, Nuclear Magnetic resonance...)
Biomagnetism
(magnetoencephalography [MEG], magnetocardiogram)
Scanning SQUID microscopy
Geophysical applications of SQUID
(oil prospecting, earthquake prediction, geothermal energy surveying)
Higher Temperature SQUIDs
(nondestructive testing of materials...)

68. Fig.2 Neuromag Ltd.122
sensor array
Fig.1 Neuromag Ltd.122
MEG system
Arrays of gradiometer dc SQUID detectors are
contained within a helmet surrounded by a liquid
helium reservoir for cooling
Fig. MRI scan of a human scull

69. Uses of SC magnets

70. Transmission Lines
15% of generated electricity is dissipated in transmission lines
Potential 100-fold increase in capacity
BNL Prototype: 1000 MW transported in a diameter of 40 cm
Pirelli Cables & Systems

71. Telecommunications Conductus Clearsite system
Superconductors are used as efficient filters in cellular telephone towers (now 700 worldwide)
Separate signals of individual phone calls.
Because of electrical resistance, conventional interference filters eat away part of the signal.
Conductus Clearsite system

72. Superconducting magnets
An electrical current in a wire creates a magnetic field around a wire. The strength of the magnetic field increases as the current in a wire increases. Because SCs are able to carry large currents without loss of energy, they are well suited for making strong magnets. When a SC is cooled below its Tc and a magnetic field is increased around it, the magnetic field remains around the SC. If the magnetic field is increased to a critical value Hc the SC will turn normal.
A typical Nb3Sn SC magnet.
It produces 10.8T with a current
of 146A. Bore diameter is 3.8 cm.
Support a very high current density with a very small resistance
A magnet can be operated for days or even months at nearly constant field
Cross-section of multifilament
Nb-Ti of 1mm overall diameter,
consisting from mm
filaments