psfc library - introduction to fusion energy · 2013. 1. 25. · nuclear energy •a huge amount of...

Introduction to Fusion Energy

Jerry Hughes

IAP @ PSFC

January 8, 2013

Acknowledgments: Catherine Fiore, Jeff Freidberg, Martin Greenwald, Zach Hartwig, Alberto Loarte,

Bob Mumgaard, Geoff Olynyk

Presenter’s e-mail: [email protected]

Questions to answer

• What is fusion?

• Why do we need it?

• How do we get it on earth?

• Where do we stand?

• Where are we headed?

What is fusion, anyway?

Fusion is a form of nuclear energy

• A huge amount of energy

is released when isotopes

lighter than iron combine

to form heavier nuclei,

with less final mass

• It is an ubiquitous energy source in the universe

• It is not (yet) a practical energy source on earth

2mcE

//upload.wikimedia.org/wikipedia/commons/a/a0/Einstein_patentoffice.jpg

Terrestrial energy sources have their origin in the nuclear fusion reactions of stars

Supernova produces radioactive elements

Solar heating of the Earth drives atmospheric

circulation, water cycle

Sun illuminates

Earth


Geothermal

Nuclear fission

Decay of radioactive particles generates

heat in Earth’s interior

Supernova produces radioactive elements Splitting radioactive

particles generates heat

Solar heating of the Earth drives atmospheric


Sun illuminates

Earth


Geothermal

Nuclear fission




particles generates heat Wind

Hydroelectric Solar heating of the Earth drives atmospheric


Running water turns

turbines

Atmospheric circulation

turns turbines

Sun illuminates

Earth


Geothermal

Nuclear fission




particles generates heat Wind

Hydroelectric Solar heating of the Earth drives atmospheric


Running water turns

turbines

Atmospheric circulation

turns turbines

Sun illuminates

Earth

Absorption of light for electricity generation

Solar

Photosynthesis generation of biomass

Burn ‘em

Biomass

Fossil fuels

What are the prospects for nuclear fusion on Earth?

• Scientists demonstrated its use as a weapon in 1952

• For 50 years, scientists and engineers have been working create controlled nuclear fusion in the laboratory in order to exploit the fusion reaction as a practical energy source.

BOMB =

What are the prospects for nuclear fusion on Earth?

• Scientists demonstrated its use as a weapon in 1952

• For over 60 years, scientists and engineers have been working create controlled nuclear fusion in the laboratory in order to exploit the fusion reaction as a practical energy source.

BOMB =

REACTOR =

Why do we need fusion?

Earth-dwellers want to consume more energy . . .

. . . a lot more

18

What Are The World’s Energy Options?

Nothing obviously easy

● Burning fossil fuels (currently 80%) even if there was enough,

must contend with climate change + pollution: is large-scale CO2

capture and storage feasible?

● Nuclear fission – safety, proliferation concerns (but cannot avoid if

we are serious about reducing fossil fuel burning; at least until

fusion available)

● Biofuels – can this be made carbon neutral? Land and water use

issues

● Solar - need breakthroughs in production and storage

● Wind, Tidal – storage and land use issues, but could fill niche

19

Pros and Cons of Fusion

Pros

• Abundant, high energy density fuel (D + Li)

• No greenhouse gases (nor NOX, SOX, particulate emission)

• Safe – no chain reaction, ~1 sec worth of fuel in device at any one time

• Minimal “afterheat”, no nuclear meltdown possible

• Residual radioactivity small; products immobile and short-lived

• Minimal proliferation risks

• Minimal land and water use

• No seasonal, diurnal or regional variation – no energy storage issue

Cons

• It doesn’t work yet (turns out to be a really hard problem)

• Capital costs will be high, unit size large (but with low operating costs)

Fusion, like all nuclear energy, produces a tremendous amount of energy from a very small mass of reactants.

7

• Typical energy scales for chemical bonds – electron-volts (eV)

• Typical energy scales for nuclear reactions – millions of electron-volts (MeV) (E=mc2)

• This means that a gigawatt-class fusion power plant will use about a pickup truck full of fuel (lithium and deuterium) per year.

• Compare to a 1 GWe coal plant – nearly 8,000 tons of coal per day!

3 days worth of coal supply for a 500 MWe plant

Fusion plants would have reduced environmental impact relative to many renewables

27

Wind, Solar, Hydro: substantial changes to the landscape needed to generate the first gigawatt Wind, Solar: lacking an energy storage solution

How do we get controlled nuclear fusion on Earth?

Back to the Future (“Mr. Fusion”)

We’re not quite to this point yet . . .

Spider-Man II

SPF 35,000,000,000, anyone?

How do we really get controlled nuclear fusion on Earth?

Two types of nuclear reactions:

• Fission – split heavy nuclei

• (e.g. Uranium)

• Fusion – fuse light nuclei

• (e.g. hydrogenic isotopes)

26

The most energetically favorable fusion reaction is between deuterium (D) and tritium (T)

D + T → He + n + 17.6 MeV

27

• Neutron : 0n1

80 % of reaction energy

==> Not Confined

==> Energy output and

tritium production

•Alpha particle : 2He4

20 % of reaction energy

==> Confined

==> Plasma Self Heating

Fuel Supply - Fusion • Plenty of D from the ocean • No natural T – half life = 12 years • Need to breed T in the reactor

Li-6 + n → He + T + 4.8 MeV • Li-6 is 7% of natural lithium • 1000’s of years of natural lithium

28

Fuel for a fusion power plant:

30 t/day seawater (extract deuterium)

350 kg/yr lithium (breed to tritium)

Problem: Nuclei do not play well together

29

+ +

• Like charges repel (Coulomb force)

• Throw them at each other and they tend to scatter

• Huge energies are needed to overcome this repulsive force

Problem: Nuclei do not play well together

• Like charges repel (Coulomb force)

• Throw them at each other and they tend to scatter

• Huge energies are needed to overcome this repulsive force 30

+

+

31

The Probability Of D-T Fusion Is The Greatest When The Nuclei Have About

100 Kev Of Kinetic Energy

• Even at the optimum energy,

the nuclei are much more

likely to scatter elastically

than to fuse!

• Therefore, nuclei must be confined over numerous scattering times this puts the fuel into a thermodynamic equilibrium

• Significant fusion rate requires fuel to be confined at >100 million degrees!

At the high temperatures required for the fusion reaction, the deuterium and tritium are in the plasma state.

10

• When energy is added to matter, phase changes can occur new physical properties.

• When sufficient heat energy is added to matter, bound electrons strip from the nuclei

• Plasma = “soup” of negatively charged electrons and positively charged nuclei.

Add heat


10




Solid / liquid / gas Plasma

Neutron

Proton

Add heat

e– e–

e–

e–


10




Solid / liquid / gas Plasma

Neutron

Proton

Add heat

e– e–

e–

e–

In plasma physics, we measure temperature in eV, where 1 eV = 11,600 K

Typical fusion plasma temp = 10 keV 100 million degrees

35

Most of the visible universe is composed of plasma

. . . not all of it is fusing

36

High confinement is needed for plasma fusion

• Our goal: get the required temperature with the least amount of heating power

• Energy confinement time is the ratio of stored energy to heating rate.

• In a fusion reactor that heat would come from the fast a particles (charged, so they are confined by the magnetic field)

ETotal stored energy Joules

Heating rate Watts(sec)

( )

( )

“Fuse it or lose it.”

Conditions needed for a self-sustaining fusion plasma

• We need enough plasma: (air/100,000)

• At a high enough temperature: (air x million)

• Holding its heat for a long enough time:

• For a sustained fusion plasma – Lawson Criterion

37

20 310n m

15T keV

2 sec

8 secp atmn T τE ≥ 3x1021

[keV s m−3]

38

Lithium

compound

A complete power plant will need to satisfy Lawson criterion, breed tritium and collect heat to drive turbines

to actually make electricity and put it on the grid.

How do we hold together a hot dense plasma?

40

Approaches To Fusion Energy

• Gravitational Confinement (300 W/m3) – In a deep gravitational well, even fast

particles are trapped.

– Very slow: E ~ 106 years, burn-up time = 1010 years

● Inertial Confinement (1028 W/m3)

– Heat and compress plasma to ignite plasma

before constituents fly apart.

– Like a little H-bomb

– Capsules would need to be burned with high

gain, high rep rate for reactor practicality

● Magnetic Confinement (107 W/m3)

– Uses the unique properties of ionized

particles in a magnetic field

41

Gyro-radius

Gyro-frequency

Gyro-motion Of Charged Particles Enables Magnetic Confinement, perpendicular to B-field

At B = 5T, T = 10keV

• e = 0.067 mm

• i = 2.9 mm

• R/ i > 1,000

• e = 8.8 x 1011 rad/sec (mwaves)

• i = 4.8 x 108 rad/sec (FM radio)

Ionized particles are deflected by the Lorentz force and bent into circular orbits.

mV c mT

qB B

c

eB

mc

What about the ends?

42

● At the temperatures involved, ions are moving at over 1,000 km/s

● For a practical device, the end losses must be eliminated

43

Close the ends, and . . .

“Donuts. Is there anything they can’t do?” --H. Simpson

. . . toroidal confinement is born

44

Magnetic Confinement In Toroidal Devices

• Solution 1: Torus solves the end-loss problem

• Problem 2: In a simple toroidal field, particle drifts lead to charge separation

B B

Bt

Bp

Bt

Bp

Jt

Bz

● Solution 2: Add poloidal field, particles sample regions of inward and outward drift.

● Problem 3: Hoop stress from unequal magnetic and kinetic pressures.

● Solution 3: Add vertical field, to counteract hoop stress.

● Magnetic confinement experiments are variations on this theme.

Bt E EB drift

Hoop Stress

45

Two Promising Strategies To Create This Configuration

● Poloidal field from current in the

plasma itself.

● Axisymmetric – good

confinement

● Current is source of instability

● Poloidal field from external coils

● Intrinsically steady-state

● Non-axisymmetric – good

confinement hard to achieve

● More difficult to build

Tokamak Stellarator

Poloidal magnetic field coil

Central solenoid

Toroidal magnetic field coil

Poloidal magnetic field

Plasma current

Toroidal magnetic field

What makes a tokamak?

14

Toroidal magnetic fields coils to create the primary toroidal confinement field

Central solenoid coils to create toroidal plasma current for secondary poloidal confinement field

Poloidal magnetic fields coils to create fields for plasma control and shaping

What makes a tokamak?

14

Toroidal magnetic fields coils to create the primary toroidal confinement field

Central solenoid coils to create toroidal plasma current for secondary poloidal confinement field

Poloidal magnetic fields coils to create fields for plasma control and shaping Helical field lines associated with a tokamak plasma

48

Plasma Is Confined On Closed Nested Flux Surfaces

• Magnetic field lines are helical and lie on closed, nested surfaces – flux surfaces, Y = const.

• To lowest order, particles are “stuck” on flux surfaces

• Confinement should be great!

How is the tokamak doing?

50

Steady progress has been made towards demonstrating fusion, particularly with tokamaks

51

Steady progress has been made towards demonstrating fusion, particularly with tokamaks

ITER (2027?)

• The ratio of fusion power produced to plasma heating power supplied is defined as capital Q: Q=1 Breakeven Q=∞ Ignition (no external heating)

𝑄 =𝑃fusion𝑃heating

Turbulence is rampant in high energy plasmas, degrading confinement

15

• Early calculations made overoptimistic predictions of tokamak confinement

• Turbulence was not taken into account!

• Turbulent eddies carry heat and particles out of the plasma hundreds of times faster than random collisions alone would

One frame of a simulation of turbulence in the DIII-D using GYRO (J. Candy, General Atomics)

53

Go large: ITER

54

Go large: ITER

● Plasma major radius = 6.2m

(twice the size of JET,

currently the world’s largest

tokamak)

● Plasma volume = 840 m3

● Fusion power 500 MWt

(with auxiliary power of

~50MW)

The ITER Mission: Demonstrate the scientific and technological feasibility of fusion energy

20

ITER construction site on Sept. 17, 2012 near Vinon-sur-Verdon, Provence-Alpes-Côte d'Azur, France

Tokamak Assembly Hall

Headquarters (500 staff)

Tokamak Seismic Isolation Pit

Rendering of ITER tokamak plus cryostat

Cadarache

• Joint effort among China, EU, India, Japan, Korea, Russia, US

• Political origin: 1985 Geneva summit • ITER agreement reached in 2006 • Construction began in 2010 in France • Construction cost > €10B • First plasma: 2020 • D-T operations: 2027

Fusion experiments around the world today are conducting research in support of ITER’s mission.

5

Alcator C-Mod Cambridge, MA, USA

DIII-D, San Diego, CA, USA

ASDEX Upgade Garching, Germany

EAST (HT-7) Hefei, Anhui, China

Joint European Torus (JET) Culham, Oxfordshire, UK

JT-60SA (under construction) Naka, Japan

KSTAR, Daejeon, Republic of Korea

SST-1, Gandhinagar, Gujarat, India

Tore Supra, Cadarache, France

Across the street is a real live tokamak

• C-Mod is a compact device with some pretty hefty parameters

– Magnetic field at the plasma

center up to 8T (>100,000 x Earth’s surface magnetic field)

– Plasma densities span the range expected for reactors

– Volume averaged plasma pressure of 2 atmospheres (world record)

– Heat flux exhaust as high as 0.5GW/m2

Alcator C-Mod

Alcator C-Mod Tour: Thursday 1/10 @1:30pm

What you won’t see on the tour Armored Inner Column

RF Wave-Based Heating Sources

(Current Drive Launcher not in view)

Power handling divertor

Molybdenum Protection Tiles (Tmelt = 2623⁰C

Examples of R&D on existing tokamaks like C-Mod

ITER and reactors will have to cope with heat exhaust

• 20% of fusion power is used to re-heat the core (a particles)

• This must either be radiated away or conducted to the divertor plates

• Must observe material limits of 10MW/m2

Radiant power + neutrons

Heat flowing to divertor

The consequences of excessive local heat flux on surfaces can be severe

Tiles removed following high power C-Mod operation

Controlled impurity injection is a way to mitigate heat loads

• Excess thermal radiation in core plasma reduces temperature, fusion performance

• Instead, localize radiation to the edge

No

rmal

ized

co

nfi

nem

ent

Fraction of power reaching outer divertor

Regulation of edge profiles is an important issue

• ITER requires an edge transport barrier to achieve desired performance (Q=10)

• Barrier is self-regulating – Large pressure gradient in

edge drives “bootstrap current”

– Combined, these lead to plasma instabilities that limit the attainable edge pressure

– Result is usually a regular ejection of hot plasma into the periphery

Projections indicate that the ITER edge would be regulated to nearly 100 kPa – likely sufficient for its mission

• Edge-regulating instabilities also help expel unwanted impurities from core

– Helium ash

– Slightly heavier nuclei introduced into the edge for heat load control (neon, argon)

– Even heavier nuclei from the wall (tungsten)

• Core impurities dilute the fuel and lead to increased bremsstrahlung radiation losses

• BUT:

• Each discrete burst in ITER (at about 1Hz) would dump about 1MJ of energy into the divertor

• Need to mitigate these!

• High performance plasma operation possible without density/impurity buildup

• Edge profiles regulated by naturally occurring turbulence

• “I-mode”: A major breakthrough that rivals the discovery of the edge transport barrier in 1982

What lies in fusion’s future?

The path to an economic tokamak fusion reactor requires solving several remaining physics and technology problems.

● Very large, high-field, superconducting magnets needed

– Mechanical and thermal stresses

– Proximity to high neutron flux

● First wall material Issues

▫ Power handling

▫ Erosion – high energy and particle fluxes

▫ No tritium retention

● Must close fuel cycle by keeping tritium breeding ratio above 1

● Steady state operation means we need non-inductive sources of current

● Auxiliary heating

● Disruption prediction and mitigation

● Ease of maintenance – high availability required

The current path to a reactor could put fusion energy on the grid during the 21st century

19

ITER online 2020’s

“DEMO” 2045?

Commercial plants 2060?

Existing tokamak experiments in USA, EU, Japan, China, India, Korea, etc. work on technical challenges.

JET

EAST

ASDEX-U

DIII-D

C-Mod JT-60SA

Tore Supra

SST-1 KSTAR

IFMIF (Europe)

FNSF/FDF/Pilot (USA)

Demonstrate the scientific and technological basis of magnetic fusion energy

Parallel facilities to research wall materials for 14.1 MeV fusion neutron environment

72

Stellerator research also remains active

W7-X

LHD

Recent developments in superconductor technology mean that the path to a reactor could be faster than originally envisioned.

22

The “Vulcan” concept – developed by 22.63 class at MIT in 2010, published as 5 papers

Double-walled replaceable vacuum vessel

Demountable high-temperature superconducting coils

High-field-side high-efficiency current drive

10

100

1000

10000

0 5 10 15 20 25 30 35 40 45

Applied Field (T)

JE

(A/m

m²)

YBCO B|| Tape Plane

YBCO B Tape Plane

2212

RRP Nb3Sn

Bronze Nb3Sn

MgB2

Nb-Ti

Figu

re c

ou

rtes

y o

f N

atio

nal

Hig

h M

agn

etic

Fie

ld L

abo

rato

ry

Engineering critical current-density at 4.2K

ITER

Nb3Sn (ITER) is brittle, so

coils are baked after

winding

YBCO and Nb-Ti just need

to be wound

New developments in superconductor technology mean a

smaller, more maintainable fusion

reactor than the ITER-like reactor

that was previously envisioned.

There are many uncertainties, but projections show fusion can be cost competitive with other sources of electricity

23

• A number of studies using systems codes have been carried out to assess the cost of electricity (CoE) with magnetic fusion

• While CoE from the first demonstration power plant (known as “DEMO”) are high, estimates for a mature fusion power plant come in at 6.6 ¢/kWh, comparable to competing technologies.

• Factored in engineering, safety, operating costs, maintenance, dismantle/disposal, etc.

• Economic case for fusion becomes stronger if carbon emission becomes more expensive. Fusion makes no direct emissions of any kind. (CO2, SOX, NOX, etc.)

75

Summary

● Fusion holds out the possibility of a safe, environmentally benign

power source

● The science and technology are extremely challenging

● But… steady progress has been made

● We’re poised to take a major step, an experiment to demonstrate

the scientific and technological feasibility of fusion energy

● A path forward to fusion exists, and there will be plenty of

scientific and engineering opportunities along the way

Conclusion: Fusion energy is critical research that will help humanity meet its energy needs in the future.

29

“The days of inexpensive, convenient, abundant energy sources are quickly drawing to a close … We must act now to develop the technology and infrastructure necessary to transition to other energy sources. Policy changes, leap-ahead technology breakthroughs, cultural changes, and significant investment are requisite for this new energy future. Time is essential to enact these changes. The process should begin now.”

— U.S. Army Corp of Engineers, 2006.

Fusion energy was selected by the National Academy of Engineering as one of the 14 Grand Engineering Challenges to improve humanity’s lot in the 21st century.

— See http://www.engineeringchallenges.org

psfc library - introduction to fusion energy · 2013. 1. 25. · nuclear energy •a huge amount of...

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