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