superconductivity - 임기조 교수님 홈페이지 입니다. · pdf file ·...

1

Superconductivity

Prof. Kee-Joe Lim

[email protected], 261-2424

School of Electrical and Computer Engineering

Chungbuk National University

http://www.cbucc.com

2015/9/1

mailto:[email protected]

http://www.cbucc.net/

2

Superconductivity technology

Fundamentals

(Zero resistance)

&

(Meissner effect)

3

- Perfect conduction -----> Zero electrical resistance

- Perfect diamagnetism ----> Meissner effect

- 3-D envelopes for critical temperature, magnetic field, current density

- Type I and Type II superconductors

- AC loss

- HTS

- Popular superconductors : NbTi, Nb3Sn, Nb3Al, Nb, YBCO,

BSCCO, TBCCO, ...

Summary on superconductivity

01

4

Perfect conductor

(Electrical resistivity of superconductor ~ Less than 10-20 ohm.cm)

5

Temperature, T

Superconductor (e.g. Pb)

Tc

Normal metal

(e.g. Ag)residual

00

A superconductor such as lead evinces a transition to zero resisitivityat a critical temperature Tc (7.2 K for Pb) whereas a normal

conductor such as silver does not, and exhibits residual resisitivity atthe lowest temperatures.

6

Meissner effect (perfect diamagnetism) -

-> figure

Discovered by Meissner

and Ochsenfeld in 1934,

the Meissner effect

describes the absence of

magnetic field within the

bulk of a superconductor

(perfect diamagnetism).

Experimental validation of

Meissner effect.

8

Magnetic levitation using superconductivity

9

Left: A magnet over a superconductor becomes levitated. The superconductor is a perfect

diamagnet which means that there can be no magnetic field inside the superconductor.

Right: Photograph of a magnet levitating above a superconductor immersed in liquid nitrogen

(77 K). This is the Meissner effect. (SOURCE: Photo courtesy of Professor Paul C.W. Chu.)

N

SMagnet

Surface currents

Superconductor below Tc

Magnet

Superconductor above Tc

N

S

11

<교재내용>

t

BE

000

t

BE

Zero resistance가 B=0의 원인은 아니다.

초전도체에서는 B=0 이다. 어떻게 이해하여야 할까 ?

0)(0 MHB HHM r )1(

01 B,0r

초전도체는 완전반자성체(perfect diamagnetic materials) 이다.

12

The Meissner effect. A superconductor cooled below its critical temperature expels all magnetic field lines

from the bulk by setting up a surface current. A perfect conductor (σ=∞) shows no Meissner effect.

15

Brief history of superconductivity

1908 Helium liquefied by Kammerlingh Onnes

1911 Superconductivity of Hg is discovered. R = 0, 4.2K

1913 Superconducting magnet concept

1916 Failed attempt to make superconducting magnet

1934 Meissner effect B = 0.

1930 Thermodynamics of Type I superconductor

1935 Penetration depth,

Type II superconductor (PbBi) by deHaas & Voogd

1950’s S. C. Collins developed helium liquefier

Discovery of many superconducting materials

1953 Coherence length (Pippad)

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1950’s GLAG theory (Ginzbug, Landau, Abrikosov, Gdkov)

1957 BCS theory (Bardeen, Cooper, Shreiffer)

Cooper pairs, two-fluid model

1961 High field, high current materials

Nb3Sn (A15 material, V3Ga, Nb3Ge), NbZr, NbTi

1960’s Flux jumping, Critical state model, Magnetic stability,

Filamentary conductor

1970’s Various superconducting magnet development

1986 High Tc (Bednorz & Muller) LaBaCuO 30K

1987 YBaCuO 92K (K. Wu & Paul Chu)

1990’s Conduction cooled superconducting magnet, HTS

electronics

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• Water : 373 K 2256 kJ/kg

• Ethylene : 169 K 481 kJ/kg

• Krypton : 120 K 116 kJ/kg

• Methane /LPG : 111 K 512 kJ/kg

• Xenon : 110 K 99 kJ/kg

• Oxygen : 90 K 213 kJ/kg

• Argon : 87 K 162 kJ/kg

• Nitrogen : 77 K 199 kJ/kg

• Neon : 27 K 86 kJ/kg

• Hydrogen : 20 K 443 kJ/kg

• Helium : 4.2 K 21 kJ/kg

Normal boiling point and latent heat of fluids

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112만불

21

In 1986 J. George Bednorz (right) and K. Alex

Müller, at IBM Research Laboratories in Zurich,

discovered that a copper oxide based ceramic-type

compound (La-Ba-Cu-O) which normally has high

resistivity becomes superconducting when ooled

below 35 K This Nobel prize winning discovery

opened a new era of hightemperature-

superconductivity research; now there are various

ceramic compounds that are superconducting above

the liquid nitrogen (an inexpensive cryogen)

temperature (77 K).

|SOURCE: IBM Zürich Research Laboratories.

25

교재 요약

• phenomenological theories

• thermodynamics ; Gorter, Casimir

• electrodynamics ; London

• atomic interpretation

• Frolich, Bardeen

• BCS theory

• experiments

• Prof. Collins (MIT)

• Maxwell, Reynolds ; Tc of isotopes of mercury –초전도가 전자와 격자진동과 유관 함을 의미 – BCS 이론의 기초가 됨

.2/1 constTM C

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제1종, 제2종 초전도체

1CH CH 2CH

제1종 초전도체(연초전도체)

제2종 초전도체(경초전도체)

External magnetic field ->

<-

반자화

T

H

J

S N

S N S N

CH

CT

CJ

3-D envelopes

자계에 의한 초전도 파괴 크라이오트론, 논리소자,기억소자

초전도 전류 초전도 전자석, 발전기, 케이블, SMES, MHD발전

완전반자성 자기부상

초전도체간의 터널효과 조셉션 접합이용, 마이크로웨이브발진기, 부성저항소자

Application

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0 2 4 6 8 10

0

0.1

Lead

Superconducting

state

Normal state

Tc

Temperature (K)

Bc (Tesla)

The critical field vs temperature in Type I superconductors.

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The critical field vs temperature in three examples of Type Isuperconductors.

0 2 4 6 8

Temperature (K)

Lead

Tin

0

0.02

0.04

0.06

0.08

Mercury

Bc

(T)

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Characteristics of Type I and Type II superconductors. B = µoH is the

applied field and M is the overall magnetization of the sample. Field inside the sample,

Binside = µoH + µoM, which is zero only for B < Bc (Type I) and B < Bc1 (Type II).

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Normal state

Superconducting state

Magnetic field lines

Vortex of flux lines

The mixed or vortex state in a Type II superconductor.

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Tc0

Normal stateBc2

Bc1

Vortex state

Meisner state

Critical magnetic field

Temperature dependence of Bc1 and Bc2.

32

T

B

J

24.5 T

18 K

~107 A cm-2

Jc

Bc2

Tc

Nb3Sn

The critical surface for a niobium-tin alloy which is a Type IIsuperconductor.

33

참고자료

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참고자료

35

참고자료

37

(a) A Josephson junction is a junction between two superconductorsseparated by a thin insulator. (b) In pactice thin film technology isused to fabricate a Josephson junction

Insulating barrier

Superconductor

(a)

SuperconductorI

I

I

V

Superconductor

SuperconductorThin film of oxide

(b)

38

I-V characteristics of a Josephson junction for positive currentswhen the current is controlled by an external circuit.

Ic

I

VO

C

Va

A

B

D

Normal current

Supercurrent

39

s

I

s

(a) T > Tc (b) T < Tc(c) T < Tc

(a) Above Tc, the flux line enter the ring (b) The ring and magnet cooled

through Tc. The flux lines do not enter the superconducting ring but stay

in the hole. (c) Removing the magnet does not change the flux in hole.

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Josephson effect

-직류 조셉션효과

V=0에서의 전류를 직류조셉션 전류, 저항은 영이고 전류치 I0는 외부회로의 전압, 저항에 의해 결정됨, 전류 I0이상에서는 조셉션 전류는 소실되고 전압이 발생되며 준입자터널전류가 흐름, 즉, 조셉션전류(V=0)에서 준입자전류 전이

조셉션효과는 자게에 민감함, 최대 조셉션 전류의 자계에 따른 변화(그림 6.11)

41

-교류 조셉션효과 조셉션 접합에 전압(V)를 인가하면 V에 비례하는 주파수 f의 교류가 발생하는 현상

VMHz [email protected]

ef

2

접합에 직류전압과 마이크로파를 동시에 인가하면, 마이크로파의 주파수가 직류전압인가시 생기는 교류전압의 주파수가 같으면 직류전압-전류 변화는 그림 6.12와 같다.

터널형 이외의 조셉션 접합(그림 6.19)

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SQUID (Superconducting Quantum Interference Device) 초전도 양자간섭소자

-외부자계가 없으면, Im=2I0 (I0는 각 접합의 최대 조셉션전류)

-외부자계 인가시, 외부자속을 연속적으로 증가시키면 내부자속은 양자화로 불연속적으로 증가,

이 되는 경우를 제외하면 내부 및 인가자속의 차이로 루프에는 전류 I’가 흐름

-접합의 전류 I/2+I’>I0이면 접합에 전압발생

-외부 자속에 대하여 Im은 주기로 변화

-SQUID 자력계; 위 원리를 이용, 2개의 접합을 이용하여 Im의 변화를 직류전압으로 검출(dc SQUID)

미소자속(지자기보다 8오더 낮음)측정;지자기 미소변동, 암석의 자화, 생체(심장, 뇌) 자기측정

0 next extint

0

43

Switching device

-최대 조셉션전류가 약한 자계에 의해 변하는 현상 이용

-구조; 절연물 기판위에 Pb, Nb등의 박막, 접합간, 접합과 제어선간에 절연막(SiO2)

-제어선에 전류가 흐르면 자계가 발생하고 접합에 가해지면 Im이 변화

-제어선 입력이 없으면 접합은 조셉션특성과 부하선 교점 A(ON상태), V0=0

-제어선 입력이 있으면, 최대 조셉션 전류는 I0’로 저하되어 B점으로 천이(OFF상태),

의 출력전압 발생

-입력전류 1mA이하, 스위칭소비전력은 전류X 1uW정도, 스위칭속도 10-11 sec

eV /20

)3(~/2 mVe

44

Memory device

-1의 기록(그림 a); I1,Iw흘리고 I2=0이면 J1 off, J2 on

-1의 기억상태(그림 b); Iw=I1=0로 하면 J1 on되어 루프에는 영구순환(CW)전류

-0의 기록(그림a);I2, Iw흘리고 I1=0……. 루프엔 영구순환(CCW)전류

-reading; 그림 b와 같이 루프전류를 입력으로하는 읽기용 스위칭소자를 설치하여 비파괴로 reading

45

조셉션접합의 기타응용

• 전압표준 교류 조셉션효과 이용( )

정확도 0.1ppm(10-7) western전지보다 1오더 높음, 1976년채용

• 고주파소자 – 발진소자; 교류조셉션효과 이용 (저주파-1012Hz), 발진전력이 낮음(1uW)

– 검파소자;조셉션소자에 가해지는 고주파 진폭에 따른 직류성분 변화이용, 수THz까지 저잡음으로 가능, 우주전파와 같은 밀리파, 서브밀리파의 검파에 이용

– 파라메트릭증폭소자; 조셉션소자의 임피던스는 유도성이며 전류에 따라 변화되는 것을 이용, 비선형 임피던스를 이용하여 증폭, 저잡음 증폭가능

Vh

ef

2

52

LTS (Low Temperature Superconductor)

53

• 상온에서 양도체인 Cu, Ag, Au, akali metal 은 초전도체 아님

• 강자성체인 Fe, Ni, Co 등은 초전도체 아님

54

[HTS (High Tc Superconductor)]

A new class of superconductors having Tc higher than ~ 25 K. All HTS discovered to

date are PEROVSKITE oxides, the first of which was La1.85Ba0.15CuO4 with Tc of 35 K,

discovered in 1986 by Bednorz & Muller of the IBM research laboratory.

YBa2Cu3O7-δ, Tc of ~ 93 K; discovered in 1987.

Bi2Sr2Can-1CunO2n+4 (BSCCO-2212, Tc of ~ 85 K or BSCCO 2223, Tc of ~ 110 K); A

fraction of lead is often substituted for bismuth, giving rise to BiPbSrCaCuO(2223),

which is processed into silver-sheathed composite superconductor tapes. BSCCO

appears more promising than YBCO for magnets.

Tl2Ba2Can-1CunO2n+4(TBCCO-2223, Tc of ~ 125 K); it appears more promising than

BSCCO for high-field applications at 77 K.

Hg0.8Tl0.2Ba2Ca2Cu3O8.33 (Tc of ~ 138 K);

60

These high temperature superconductor (HTS) flat tapes are based on (Bi2-

xPbx)Sr2Ca2Cu3O10-d(Bi-2223). The tape has an outer surrounding protective metallic

sheath. Right: HTS tapes having ac power loss below 10 mW/m have a major

advantage over equivalent-sized metal conductors, in being able to transmit

considerably higher power loads. Coils made from HTS tape can be used to create more

compact and efficient motors, generators, magnets, transformers and energy storage

devices.

| SOURCE: Courtesy of Australian Superconductors.

61

A solenoid carrying a current experiences radial forces pushing the coilapart and axis froces compressing the coil.

Mechanical

support structure

Coil windings

Radial forces

Air

Superconductor

Copper matrix

Solenoid

Superconducting electromagnets

used on MRI. Operates with

liquid He, providing a magnetic

field 0.5–1.5 T.

SOURCE: Courtesy of IGC Magnet Business

group.

Cryogenic Engineering Lab. of KAIST 66

ITER (International Thermonuclear

Experimental Reactor)


ITER


Fusion tokamak

(Utilizing large and strong

superconducting magnet)


SMES (Superconducting Magnetic

Energy Storage)


Superconducting generator

Torque tube

Torque tube

Cryogen

supply

armature

Superconducting

Filed winding

Field shield

damper

Torque t ube

76

Cryocoolers

for 1000 hp HTS (High-Tc superconductor) motor

Field winding temperature ~33 K

Cooling capacity 60 W

Max. ambient temperature 313 K

Total input power <10 kW

MTBF >9000 HRS

System cost $25,000.00

78

Superconducting power cable

81

MAGLEV

82

Principle of MAGLEV

85

Superconducting Magnet for Yamanashi MAGLEV test Line

86

On-Board Refrigeration System with GM Cryocooler of Magnetic

Levitated Train

88

MHD propulsion

89

MRI (Magnetic Resonance Imaging) system

LHe recondensing system for MRI

superconducting magnet

(Utilizing 4 K cryocooer as well as cooler

for radiation shield)

90

MRI superconducting magnet

91

NMR development

Magnetic field (T)

Sto

red

en

ergy (

MJ)

92

MSI (Magnetic Source Imaging)

http://www.4dneuroimaging.com/external_english/html/testmnl.html

-생각 중에 있는 뇌의 전기적신호를 감지할 수 있는 영상시스템

93

MAGNETOENCEPHALOGRAPHY (MEG)

-뇌자도; 뇌신경세포의 전기적활동에서 발생하는 미세한 생체자기를 초전도 센서로 획득 영상화하는 장치

94


96


97

Functional Magnetic Resonance Imaging

98

Accelerator

sc magnet

Hadron Electron Ring Accelerator

99

Superconducting electronics - SQUID (Superconducting Quantum Interference Device) at 80 K - Josephson junction - superconducting RF filter - superconducting bolometer - cryotron or RSFQ (Rapid Single Flux Quantum)

superconducting circuits for Petaflops-Scale Computer Computer

102

Superconducting RF filter characteristics (Microwave application)

103

Superconducting RF filter characteristics (Microwave application)

Semiconductor

Superconductor

104

Configuration of wireless base station


HTS(High Tc Superconductor) RF filter for PCS

106

Magnetic levitation (FES)

107

Superconducting Transition-Edge Thermometer

108

Superconductivity world in 2030

109

Lattice vibration

1

2

A pictorial and intuitive view of an indirect attraction between twooppositely travelling electrons via a lattice distorsion and vibration.

110

(a) A Josephson junction is a junction between two superconductorsseparated by a thin insulator. (b) In pactice thin film technology isused to fabricate a Josephson junction

Insulating barrier

Superconductor

(a)

SuperconductorI

I

I

V

Superconductor

SuperconductorThin film of oxide

(b)

111

I-V characteristics of a Josephson junction for positive currentswhen the current is controlled by an external circuit.

Ic

I

VO

C

Va

A

B

D

Normal current

Supercurrent

112

s

I

s

(a) T > Tc (b) T < Tc(c) T < Tc

(a) Above Tc, the flux line enter the ring (b) The ring and magnet cooled

through Tc. The flux lines do not enter the superconducting ring but stay

in the hole. (c) Removing the magnet does not change the flux in hole.

113

이하 참고자료

superconductivity - 임기조 교수님 홈페이지 입니다. · pdf file ·...

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