High explosives and flying frogs:High explosives and flying frogs: research at high magnetic fieldsresearch at high magnetic fields

• General IntroductionGeneral Introduction– HistoryHistory

• Generation of high Generation of high magnetic fieldsmagnetic fields– SuperconductingSuperconducting

– ResistiveResistive

– HybridHybrid– Pulsed:Pulsed: Long pulseLong pulse

Short Short pulsepulse

• Research at high Research at high magnetic fieldsmagnetic fields– Magneto-opticsMagneto-optics

– Diamagnetic levitationDiamagnetic levitation

– What do we do?What do we do?

Stephen Hill, Department of PhysicsStephen Hill, Department of Physics

The Magnetic Field600 BC - LodestoneThe magnetic properties of natural ferric ferrite (Fe3O4) stones (lodestones) were described by Greek philosophers.

1175 - First Reference to a CompassAlexander Neckem an English monk of St. Albans describes the workings of a compass.

1269 - First Detailed Description of a CompassPetrus Peregrinus de Marincourt, a French Crusader, describes a floating compass and a compass with a pivot point.

1040 - One of the earliest magnetic compasses A floating fish-shaped iron leaf, mentioned in the Wu Ching Tsung Yao which was written around 1040. The book describes how iron can be heated and quenched to produce thermo-remanent magnetisation. The first clear account of suspended magnetic compasses in any language was written by Shen Kua in 1088.

The Magnetic FieldThe Magnetic Field

William Gilbert (1544-1603) studied magnetism and in 1600 wrote "De magnete" which gave the first rational explanation to the mysterious ability of the compass needle to point north-south: the Earth itself was magnetic.

This opened the first era of modern physics marked by the great achievements of Galileo, Kepler, Newton and others.

1600 - Static Electricity (De Magnete)

1820 - Electromagnetism, CurrentIn 1820, a physicist Hans Christian Oersted, learned that a current flowing through a wire would move a compass needle placed beside it. This showed that an electric current produced a magnetic field.

The Magnetic FieldThe Magnetic Field

As you will see in this talk, this is the way to generate high magnetic fields.

1820 - Electromagnetism, CurrentAndre Marie Ampere showed that two parallel wires carrying current attracted each other if the currents flowed in the same direction and opposed each other if the currents flowed in opposite directions. He formulated in mathematical terms, the laws that govern the interaction of currents with magnetic fields in a circuit and as a result of this the unit of electric current, the amp, was derived from his name.

The Magnetic FieldThe Magnetic Field

Birth of 2Birth of 2ndnd era of modern physics era of modern physics

A sense of scaleA sense of scale

1 tesla 10,000 oersted (gauss)Earth's magnetic field 0.5 gauss

Text books claim strong lab field 1 teslaSaturation magnetization of Fe (1 - 2 tesla)/o

108 tesla - surface of a pulsar104 tesla - white dwarf

3 × 10-1 tesla - in a sun spot10-2 tesla - surface of sun

The Royal Swedish Academy of Sciences has awardedThe Royal Swedish Academy of Sciences has awarded

The 1985 Nobel Prize in PhysicsThe 1985 Nobel Prize in Physics

to Professor Klaus von Klitzing, Max-Planck-Institute, Stuttgart, Germany

von Klitzing was awarded the Nobel Prize for discovering the quantized Hall effect. This effect can only be observed in strong magnetic fields,strong magnetic fields, resulting in the most precise definition of the unit of resistance – the ohm.

Citation:"for his discovery of the quantized Hall effect."

The Royal Swedish Academy of Sciences has awardedThe Royal Swedish Academy of Sciences has awarded

The 1998 Nobel Prize in Physics jointly to The 1998 Nobel Prize in Physics jointly to

Professor Robert B. Laughlin, Stanford University, California, USA

Professor Horst L. Störmer, Columbia University, New York and Bell Labs, New Jersey, USA, and

Professor Daniel C. Tsui, Princeton University, Princeton, New Jersey, USA.

The three researchers are being awarded the Nobel Prize for discovering that electrons acting together in strong strong magnetic fieldsmagnetic fields can form new types of "particles", with charges that are fractions of electron charges.

Citation:"for their discovery of a new form of quantum fluid with fractionally charged excitations."

The Royal Swedish Academy of Sciences has awardedThe Royal Swedish Academy of Sciences has awarded

The 2003 Nobel Prize in medicine jointly to The 2003 Nobel Prize in medicine jointly to

Professor Paul C Lauterbur, University of Illinois, USA

Professor Peter Mansfield, University of Nottingham, United Kingdom

Citation:"for their discoveries concerning magnetic resonance imaging."

Technology drivenTechnology driven

Importance of research at high Importance of research at high magnetic fieldsmagnetic fields

• Up to 60 tesla using proven technology– Condensed matter

• Superconductivity

• Magnetism

• Correlated systems

– Magnetic resonance• EPR/NMR/MRI

– Particle physicsParticle physics

– Zero gravity conditionsZero gravity conditions

• Up to 1000 tesla - currently under development– Condensed matter

• Superconductivity

• Magnetism

• Correlated systems

– Spectroscopy of atoms

– New forms of matter

– AstrophysicsAstrophysics

Generating high magnetic fieldsGenerating high magnetic fields

• It is only practical to vary R up to a point

• Key parameter is J• Major limiting factors

– Power supply– Joule heating– Magnetic forces

Biot-Savart law B log(Rout/Rin)where Rout and Rout represent the innerand outer radii of a solenoidal magnet

B current density J3

34o d r

r

J rB

Method 1: Eliminate Joule heatingMethod 1: Eliminate Joule heatingSuperconducting magnetsSuperconducting magnets

• Combination of Nb3Sn and NbTi

• Wires permeated with epoxy

Nb3Snwire

Typical specs

Field: 18/20 T @ 4.2/2.2 KMax current 122 AVoltage < 10 VInductance 240 hSize Ro 6", Ri 1", h 12"Wire diameter 1 mm

Filament diameter 75 m

Pros Pros and and cons... cons...World record: 25 teslaWorld record: 25 tesla

Magnet is cheapMagnet is cheapLow power (< kW)Low power (< kW)Can be persistentCan be persistentPortablePortableEasy to operateEasy to operateLarge sample spaceLarge sample spaceExtremely reliable*Extremely reliable*

Requires liquid HeliumRequires liquid HeliumExtremely high inductanceExtremely high inductance

slow ramp ratesslow ramp ratesB field kills superconductivityB field kills superconductivity 2 MJ stored energy @ B2 MJ stored energy @ Bmaxmax

*If operated correctly*If operated correctly

Method 2: Resistive magnetsMethod 2: Resistive magnets

3 coils in seriesInner coil consists of 2 coils in parallelCooling water flows axially through holesElliptical holes minimize stressesConductor: Cu/Ag alloyInsulation: Kapton

Specifications...Specifications...

• NHMFL (Tallahassee, FL)– Two 20 MW supplies

• Vm = 500 V; Im = 20 kA

– Ripple < 10ppm

– Two 30+ T magnets (32mm bore)

– 25 T, 52mm

– 20 T, 200mm

– 24.5 T, 32mm bore - high homogeneity for NMR

Max field: 34 teslaMax field: 34 tesla

• World record magnet– 34 tesla @ 38 kA

– 500 V max

– 19 MW!!

– Water 140 liters/sec T=35oC ( 20 MW)

Also: Netherlands, France, Japan

Method 3: Method 3: Hybrid magnetHybrid magnetSuperconducting and resistiveSuperconducting and resistive

• Superconducting outer• Resistive inner• V. expensive to run• Not user friendly• Days to prepare• Dangerous! Energy

stored in supercon is several hundred MJ

Max field: 50 tesla ?Max field: 50 tesla ?

Whereabouts:Tallahassee, FL – (world record 45 T) Nijmegen, NL – (under construction)Tsukuba, JapanMIT - decomissioned

Method 4: Pulsed magnetsMethod 4: Pulsed magnetsNon-destructive, short pulseNon-destructive, short pulse

Wire: Cu/Ag and Cu/Nb Alloy

Kapton insulation

Reinforcement:Glass/carbon fiber

• Coil consists of few turns– Keep inductance low

• Magnet cooled to 77 K prior to pulse– Increases conductivity

• Relatively cheap and easy to build

SpecificationsSpecificationsMax field: 70 teslaMax field: 70 tesla

Capacitor drivenCapacitor driven1.5 megajoules at 10 kV(.44 magnum slug 1 kJ)Imax = 20 kA

63 T, 15mm, 7/35ms50 T, 24mm, 6/30ms 42 T, 24mm, 100/500ms1 pulse/hour to 63 tesla

500 - 800 pulses, then...

10 mm SP

0 5 10 15 20 25 30 35

0

10

20

30

40

50

60

70

80

24 mm SP

Mag

netic

Fie

ld (

T)

Time (ms)

0 5 10 15 20 25 30 35

0

10

20

30

40

50

60

70

80

15 mm SP

Mag

netic

Fie

ld (

T)

Time (ms)

Non-destructive, Non-destructive, long pulselong pulse

260 ton flywheel1.4 gigawattMagnet ~90 MJCan deliver 270 MJ

60 T for 0.1 s or 50 T for 0.5 s32 mm bore1 shot/hr

NHMFL/LANLAmsterdam

0

10

20

30

40

50

60

0 1 2 3

MA

GN

ET

IC F

IEL

D (

tesl

a)

TIME (seconds)

Challenges in Producing High Magnetic Fields

Pressure Under Water 4 m Ears 6 psi 1000 m Submarine 1000 psi 4000 m Ocean Floor Submersible 6000 psi

Pressure inside NHMFL Magnets 80T Pulsed Magnet 200,000 psi (1.3GPascals, 130 kg/mm2)

…exceeds the strength of most materials… …within a factor of three of theoretical ultimate tensile strength…

Strong Electromagnets

Generate HUGE Forces

Flux compressionFlux compressionSingle stageSingle stage

Max field: Max field: 200 tesla200 tesla

Magnet is destroyedMagnet is destroyed

Sample oftenSample oftensurvivessurvives

3 stage explosive flux compression3 stage explosive flux compression

BeforeBefore DuringDuring

AfterAfter

3 Stage 850 tesla generator3 Stage 850 tesla generator

Shockwave

Machined High Explosives

1st Stage

2nd

3rdSample

Syncronous Detonators

Foam Support

Optical Reflectivity of GaAs sampleOptical Reflectivity of GaAs sample60x103

55

50

45

40

Re

felc

tivi

ty S

ign

al (

arb

. un

its)

2 3 4 5 6 7 8 9100

2 3 4 5 6 7 8

Magnetic Field (T)

60x103

50

40

30

20

Fara

da

y Ro

tatio

n (a

rb. u

nits)

Optical Signals @ 75 K - Dirac MC1-D GaAs QW Reflectivity @810 µm Quartz Faraday Rotation @ 632.8 µm

J. S. Brooks and C. H. Mielke June 18, 1997

....Some fun with strong magnetic fields....Some fun with strong magnetic fields

Everything is magnetic.....Everything is magnetic.....

Diamagnetic levitationDiamagnetic levitation• Molecular diamagnetism

– Common to all matter

– Usually obscured by other forms of magnetism

• Becomes apparent in strong magnetic fields

• Study effects of micro-gravity– Crystal growth

– Plant growth

Basic principalBasic principal

The work was first featured in Physics World, April 1997, p. 28 E.H. Brandt, Science 243, 349 (1989) and Physics World, September 1997"Of Flying Frogs and Levitrons" by M.V.Berry and A.K. Geim, European

Journal of Physics, v. 18, p. 307-313 (1997). http://www-hfml.sci.kun.nl/hfml/levitate.htmlhttp://www.nhmfl.gov/movies/levitation/index.html

m = (/o)VB Fmag = mB = (/o)VBB Fmag = (/2o)VB2

Fgrav = Mg = Vg

levitation requires:

B2 > 2og/

V is volume typically -10-5 JT-2kg-1

103 m-3

requires B2 103 T2m-1

Taking l 0.1 mWe get B 10 tesla

Very briefly..... Very briefly..... What do we do?What do we do?

Synthesis and characterization:Synthesis and characterization:Christou group, UF chemistryChristou group, UF chemistryAdvanced characterization:Advanced characterization:High frequency EPR, UF physicsHigh frequency EPR, UF physics

Nano-scale Nano-scale Single MoleculeSingle MoleculeMagnetsMagnets

1 Nano-1 Nano-metermeter

The Future: writing informationThe Future: writing informationto individual moleculesto individual molecules

MnMn1212AcAc

Organic superconductorsOrganic superconductors

• One can easily tailor materials with desired propertiesOne can easily tailor materials with desired properties

• The materials are intrinsically clean, The materials are intrinsically clean, i.e.i.e. very pure very pure

• Organic conductors exhibit virtually all known electronic Organic conductors exhibit virtually all known electronic states of matter, states of matter, e.ge.g: :

Metal, insulator, magnetism, quantum Hall effect, Metal, insulator, magnetism, quantum Hall effect, superconductivity (conventional and exotic forms). superconductivity (conventional and exotic forms).

SummarySummary

• History of magnetism and research at high magnetic History of magnetism and research at high magnetic fieldsfields

• Overview of different ways to generate high magnetic Overview of different ways to generate high magnetic fieldsfields

–SuperconductingSuperconducting

–Resistive and hybridResistive and hybrid

–Long & short pulse (non destructive and destructive)Long & short pulse (non destructive and destructive)

• Overview of worldwide user facilitiesOverview of worldwide user facilities

• Fun experiments - diamagnetic levitationFun experiments - diamagnetic levitation

• Examples of what we doExamples of what we do