josephson effect (see also hand-out) in 1962 josephson predicted cooper-pairs can tunnel through a...
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Josephson effectJosephson effect (see also hand-out)(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:
21sin cJJ
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 TMagnetic field of heart: 10-10 TMagnetic 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 systemArrays 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 magnetsUses of SC magnets
Transmission LinesTransmission 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
TelecommunicationsTelecommunications
• 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
Superconducting magnetsSuperconducting magnetsAn 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 multifilamentNb-Ti of 1mm overall diameter,consisting from 13255 5-mfilaments
Other Uses of SuperconductivityOther 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-THigh-Tc c SuperconductivitySuperconductivity
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