SUPERCONDUCTIVITY

actorrattleUrban and Civil

Nov 15, 2013 (3 years and 7 months ago)

74 views

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:



2
1
sin




c
J
J
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.

Brian D. Josephson


The Discovery of Tunnelling Supercurrents


The Nobel Prize in Physics 1973


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: 10
-
14

T

Magnetic field of heart: 10
-
10

T

Magnetic field of brain: 10
-
13

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...)

JJ’s essential in Superconducting Interference Devices

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.2

Neuromag Ltd.122


sensor array

Fig.

MRI scan of a human scull

Uses of SC magnets

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

Telecommunications



S
uperconductors
are used as
efficient
filters

in cellular telephone
towers

(now 700 worldwide)




S
eparat
e

signals of individual
phone calls.




Because of electrical resistance,
conventional interference filters eat
away part of the signal.



Conductus Clearsite system

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.



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


A typical Nb3Sn SC magnet.

It produces 10.8T with a current

of 146A. Bore diameter is 3.8 cm.

Cross
-
section of multifilament

Nb
-
Ti of 1mm overall diameter,

consisting from 13255 5
-
m
m

filaments

Other Uses of Superconductivity





Fault current limiters



Electric motors



Electric generators



Petaflop computers (thousand trillion
floating point operations per second)

Applications of Superconductivity

Trade off between:


Cost Saving
and

Cost Increase

Zero resistance, no
energy lost, novel
uses…

Need refrigeration,
fabrication costs….

High
-
T
c
Superconductivity

Alex Müller and Georg Bednorz


Paul Chu

164 K

295 K,room temp

373 K,BP of water

273 K,FP of water

77 K,Liquid Nitrogen

4.2 K,Liquid Helium

138 K,Highest Tc for HgBaCaCuO

K.A. Muller J. G. Bednorz


The Discovery of superconductivity in ceramic materials



The Nobel Prize in Physics 1987