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Studies of the Cryogenic Part with Load Lock System
T. Eisel, F. HaugCERN TE-CRG-CI
October 19th, 2011, Page 1
Superconductivity - 100 years
Heike Kamerlingh Onnes (Leiden)• 1908 liquefaction of helium• 1911 electrical resistance
measurements of mercury at low temperatures (< 4.2 K)
• 1913 Nobel Prize
http://de.wikipedia.org/wiki/Heike_Kamerlingh_Onnes
http://www.tikalon.net/blog/blog.php?article=2011/superconductivity
Studies of the Cryogenic Part with Load Lock System
T. Eisel, F. HaugCERN TE-CRG-CI
October 19th, 2011, Page 2 Superconductivity
• Bardeen –Cooper –Schrieffer (1957)
– e- are fermions, Pauli exclusion principle– Energy reduction for FA
Theory behind – BCS theory
http://eng.super-kics.or.kr/infos/history
Studies of the Cryogenic Part with Load Lock System
T. Eisel, F. HaugCERN TE-CRG-CI
October 19th, 2011, Page 3 Superconductivity
• Cooper pairs– Between e- (different spin)– Attractive force (i+ and e-)– Positive charge attracts the following e-
• Time delayed due to heavy i+ • Large distance between the e- • FC → 0
• Energy drop for the e- of a Cooper pair
Theory behind – BCS theory
Presentation of P.Hedegard: “Theory_Behind”
Studies of the Cryogenic Part with Load Lock System
T. Eisel, F. HaugCERN TE-CRG-CI
October 19th, 2011, Page 4 Superconductivity
• TC of pure metals:– Al @ 1.2 K– Hg @ 4.15 K– Nb @ 9.2 K
• Not superconducting:– Good normal electrical
conductor (Cu, Ag, Au)– Ferromagnetic materials
(Fe, Co, Ni)
Energy gap, TC
Superconducting
Normal conducting
Studies of the Cryogenic Part with Load Lock System
T. Eisel, F. HaugCERN TE-CRG-CI
October 19th, 2011, Page 5 Superconductivity
Meissner Ochsenfeld effect
• Superconductor is diamagnetic– Shielding of external magnetic flux by
electrical currents at its surface
• Transition to normal conducting state– For B ≥ BC → Ekin,shield_e- ≥ D
– For both: shield current or transport current (jC)
http://www.google.de/
Studies of the Cryogenic Part with Load Lock System
T. Eisel, F. HaugCERN TE-CRG-CI
October 19th, 2011, Page 6 Superconductivity
Types of Superconductors
• Type 1 Superconductor– Meissner phase
• Type 2 Superconductor– Shubnikov phase (alloys)– Magnetic flux is entering the superconductor in
quantum (normal conducting islands)
Meissner
Shubnikov
Normal conducting
http://news.sciencemag.org/sciencenow/2003/10/07-01.html
Studies of the Cryogenic Part with Load Lock System
T. Eisel, F. HaugCERN TE-CRG-CI
October 19th, 2011, Page 7 Superconductivity
Applications
• @ CERN:– electrical conductors (cables) at the LHC
for magnets (di-, quadro- sextupol), cavities– NbTi (TC=9.2 K, BC2=15 T; workhorse
among superconductors)
• Else:– MRI (Magnetic Resonance Imaging) Tim Havens – GE Healthcare
• 1977 first clinical imaging,• 30.000 scanners worldwide in 2011,• > 50% of superconductor worldwide, Script of TU Dresden
– SQUID (Superconducting Quantum Interference Devices), – Transport (ship motor, train, centrifuge, clean room)– SMES (Superconducting Magnetic Energy storage)– FCL (Fault Current Limiter) is promising
http://cdsweb.cern.ch/record/43859
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