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Introduction to Fusion

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? What is fusion, anyway? What is fusion, anyway? What is fusion, anyway? Fusion is a form of nuclear energy E  mc2 • A huge amount of energy is released when than combine to form heavier nuclei, with less final • It is an ubiquitous energy source in the • It is not (yet) a practical energy source on earth Fusion is a form of nuclear energy E  mc2 • 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 Terrestrial energy sources have their origin in the reactions of

Supernova produces radioactive elements

Solar heating of the Earth drives atmospheric circulation, water cycle

Sun illuminates Earth Terrestrial energy sources have their origin in the nuclear fusion reactions of stars Geothermal Decay of radioactive particles generates in Earth’s interior

Supernova produces radioactive elements Splitting radioactive particles generates heat

Solar heating of the Earth drives atmospheric circulation, water cycle

Sun illuminates Earth Terrestrial energy sources have their origin in the nuclear fusion reactions of stars Geothermal Decay of radioactive particles generates heat in Earth’s interior Nuclear fission

Supernova produces radioactive elements Splitting radioactive particles Wind Atmospheric generates heat circulation turns Solar heating of the turbines Hydroelectric Earth drives atmospheric circulation, water Running cycle water turns turbines

Sun illuminates Earth Terrestrial energy sources have their origin in the nuclear fusion reactions of stars Geothermal Decay of radioactive particles generates heat in Earth’s interior Nuclear fission

Supernova produces radioactive elements Splitting radioactive particles Wind Atmospheric generates heat circulation turns Solar heating of the turbines Hydroelectric Earth drives atmospheric circulation, water Running cycle water turns turbines Solar Absorption of light for generation Sun illuminates Earth Burn ‘em Photosynthesis  generation of biomass What are the prospects for nuclear fusion on Earth? • Scientists demonstrated BOMB =  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.

What are the prospects for nuclear fusion on Earth? • Scientists demonstrated BOMB =  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.

REACTOR =  Why do we need fusion? Earth-dwellers want to consume more energy ...... a lot more What Are The World’s Energy Options?

Nothing obviously easy

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

must contend with change + : is large-scale CO2 capture and storage feasible? ● Nuclear fission – safety, proliferation concerns (but cannot avoid if we are serious about reducing fossil burning; at least until fusion available) ● – can this be made neutral? Land and water use issues ● Solar - need breakthroughs in production and storage ● Wind, Tidal – storage and land use issues, but could fill niche

18 Pros and Cons of Fusion

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

• No greenhouse (nor NOX, SOX, particulate emission) • Safe – no , ~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 issue Cons • It doesn’t yet (turns out to be a really hard problem) • Capital costs will be high, unit size large (but with low operating costs)

19 Fusion, like all nuclear energy, produces a tremendous amount of 7 energy from a very small mass of reactants.

• Typical energy scales for chemical bonds – -volts (eV) • Typical energy scales for nuclear reactions – millions of electron-volts (MeV) (E=mc2) • This means that a gigawatt-class fusion plant will use about a pickup truck full of fuel ( and ) per year.

• Compare to a 1 GWe plant – nearly 8,000 3 days worth of coal supply tons of coal per day! for a 500 MWe plant Fusion plants would have reduced environmental impact 27 relative to many renewables

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. )

• Fusion – fuse light nuclei

• (e.g. hydrogenic isotopes)

26

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

1 • : 0n 80 % of reaction energy ==> Not Confined ==> Energy output and tritium production

4 • : 2He 20 % of reaction energy ==> Confined ==> Self Heating D + T → He + n + 17.6 MeV

27 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

Fuel for a plant:

30 t/day seawater 350 kg/yr lithium (extract deuterium) (breed to tritium)

28 Problem: Nuclei do not play well together

• Like charges repel (Coulomb force)

+ +

• Throw them at each other and they tend to scatter

• Huge are needed to overcome this repulsive force 29 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 The Probability Of D-T Fusion Is The Greatest When The Nuclei Have About 100 Kev Of

• 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!

31 At the high required for the fusion reaction, 10 the deuterium and tritium are in the plasma state.

• When energy is added to matter, phase changes can occur  new physical properties. • When sufficient heat energy is Add heat added to matter, bound strip from the nuclei

• Plasma = “soup” of negatively charged electrons and positively charged nuclei. At the high temperatures required for the fusion reaction, 10 the deuterium and tritium are in the plasma state.

• When energy is added to matter, phase changes can occur  new physical properties. • When sufficient heat energy is Add heat added to matter, bound electrons strip from the nuclei / liquid / Plasma e– e– Neutron • Plasma = “soup” of negatively charged electrons and e– e– positively charged nuclei. At the high temperatures required for the fusion reaction, 10 the deuterium and tritium are in the plasma state.

• When energy is added to matter, phase changes can occur  new physical properties. • When sufficient heat energy is Add heat added to matter, bound electrons strip from the nuclei Solid / liquid / gas Plasma e– e– Neutron • Plasma = “soup” of negatively Proton charged electrons and e– e– positively charged nuclei.

In plasma physics, we measure in eV, where 1 eV = 11,600 K Typical fusion plasma temp = 10 keV  100 million degrees Most of the visible universe is composed of plasma

. . . not all of it is fusing 35 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 ) Total stored energy ()  (sec)  E Heating rate (Watts)

“Fuse it or lose it.” 36 Conditions needed for a self-sustaining fusion plasma

20 3 • We need enough plasma: nm  10 (air/100,000)

• At a high enough temperature: T  15 keV (air x million) • Holding its heat for a long enough time:  2sec

• For a sustained fusion plasma –

21 n T τE ≥ 3x10 p 8 atm sec

[keV s m−3]

37 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.

Lithium compound

38 How do we hold together a hot dense plasma? Approaches To Fusion Energy

• Gravitational Confinement (300 W/m3) – In a deep gravitational well, even fast particles are trapped. 6 – Very slow: E ~ 10 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

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

Ionized particles are deflected by the Lorentz force and bent into circular orbits. At B = 5T, T = 10keV mV c mT Gyro-radius   • e = 0.067 mm qB B

• i = 2.9 mm

eB Gyro-frequency • R/ i > 1,000 c  mc 11 • e = 8.8 x 10 rad/sec (mwaves) 8 • i = 4.8 x 10 rad/sec (FM radio) 41 What about the ends?

● At the temperatures involved, are moving at over 1,000 km/s ● For a practical device, the end losses must be eliminated

42 Close the ends, and . . .

. . . toroidal confinement is born

“Donuts. Is there anything they can’t do?” --H. Simpson 43 Magnetic Confinement In Toroidal Devices

• Solution 1: solves the end-loss problem • Problem 2: In a simple toroidal field, B EB t E drift particle drifts to charge separation B B

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

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

B p ● Solution 3: Add vertical field, to counteract hoop stress. J t ● Magnetic confinement experiments are B t variations on this theme. Bz

44 Two Promising Strategies To Create This Configuration

Tokamak

● Poloidal field from current in the ● Poloidal field from external coils plasma itself. ● Intrinsically steady-state ● Axisymmetric – good ● Non-axisymmetric – good confinement confinement hard to achieve ● Current is source of instability ● More difficult to build 45 What makes a ?

Central solenoid

Toroidal magnetic Poloidal magnetic field fields coils to create Poloidal magnetic field coil the primary toroidal confinement field Central solenoid coils to create toroidal plasma current for secondary poloidal confinement field Poloidal magnetic fields coils to create Toroidal magnetic field coil fields for plasma Plasma current control and shaping Toroidal magnetic field 14 What makes a tokamak?

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 14 Plasma Is Confined On Closed Nested 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!

48 How is the tokamak doing? Steady progress has been made towards demonstrating fusion, particularly with

50 Steady progress has been made towards demonstrating fusion, particularly with tokamaks • The ratio of fusion power produced to plasma ITER (2027?) heating power supplied is defined as capital Q: 푃 푄 = fusion 푃heating

Q=1  Breakeven Q=∞  Ignition (no external heating) 51 Turbulence is rampant in high energy plasmas, 15 degrading confinement • Early calculations made overoptimistic predictions of tokamak confinement • Turbulence was not taken into account!

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

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

53 ●GoPlasma large: major radius = 6.2m (twice the size of JET, currentlyITER the world’s largest tokamak) ● Plasma = 840 m3 ● Fusion power 500 MWt (with auxiliary power of ~50MW)

54 The ITER Mission: Demonstrate the scientific and 20 technological feasibility of fusion energy • 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 Cadarache • D-T operations: 2027

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

Headquarters (500 staff) Tokamak Seismic Isolation Pit Tokamak Assembly Hall

Rendering of ITER tokamak plus cryostat Fusion experiments around the world today are conducting research 5 in support of ITER’s mission. Alcator C-Mod Cambridge, MA, USA EAST (HT-7) Hefei, Anhui, China KSTAR, Daejeon, Republic of Korea

ASDEX Upgade (JET) Garching, Germany Culham, Oxfordshire, UK SST-1, Gandhinagar, Gujarat, India

JT-60SA (under construction) Naka, Japan Tore Supra, Cadarache, France DIII-D, San Diego, CA, USA Across the street is a Alcator C-Mod 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 span the range expected for reactors

– Volume averaged plasma of 2 atmospheres (world record)

– Heat flux exhaust as high as 0.5GW/m2 Alcator C-Mod Tour: Thursday 1/10 @1:30pm What you won’t see on the tour

RF Wave-Based Armored Inner Heating Sources Column

(Current Drive Launcher not in view)

Molybdenum Protection Tiles Power handling (Tmelt = 2623⁰C Examples of R&D on existing tokamaks like C-Mod ITER and reactors Radiant power + 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 Heat flowing • Must observe material to divertor limits of 10MW/m2 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 in core plasma reduces temperature,

fusion performance • Instead, localize

radiation to the edge

Normalized Normalized confinement

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 – ash – Slightly heavier nuclei introduced into the edge for heat load control (neon, argon) – Even heavier nuclei from the wall () • Core impurities dilute the fuel and lead to increased radiation losses • BUT: • Each discrete burst in ITER (at about 1Hz) would dump about 1MJ of energy into the divertor • Need to mitigate these!

• 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 ● 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 19 the grid during the 21st century

Demonstrate the scientific and technological basis of magnetic fusion energy JT-60SA JET C-Mod ITER “DEMO” EAST Tore Supra DIII-D online 2020’s 2045? KSTAR SST-1 ASDEX-U Existing tokamak experiments in USA, EU, Japan, China, India, Korea, etc. work on technical challenges.

IFMIF (Europe) Commercial FNSF/FDF/Pilot (USA) plants Parallel facilities to research 2060? wall materials for 14.1 MeV fusion neutron environment Stellerator research also remains active

LHD

W7-X 72 Recent developments in superconductor technology mean that the 22 path to a reactor could be faster than originally envisioned. Engineering critical current-density at 4.2K 10000

YBCO B Tape Plane

YBCO B|| Tape Plane

Nb-Ti RRP Nb3Sn 1000 ITER

2212

(A/mm²)

E

J

Nb Sn (ITER) is brittle, so 100 3 Bronze coils are baked after MgB2 winding Nb3Sn YBCO and Nb-Ti just need

to be wound Figure courtesy of National High Magnetic Field Laboratory Field Magnetic High of National courtesy Figure 10 0 5 10 15 20 25 30 35 40 45 The “Vulcan” concept – Applied Field (T) developed by 22.63 class at MIT in 2010, published as 5 papers New developments in superconductor technology mean a smaller, more Demountable high-temperature superconducting coils maintainable fusion Double-walled replaceable vacuum vessel reactor than the High-field-side high-efficiency current drive ITER-like reactor that was previously envisioned. There are many uncertainties, but projections show fusion 23 can be cost competitive with other sources of electricity

• 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.)

Summary

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

● 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

75 Conclusion: Fusion energy is critical research that will help 29 humanity meet its energy needs in the future.

“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