but were afraid to ask

(1)

Everything you always wanted to know about fusion reactors,

but were afraid to ask

Minh Quang Tran

Swiss Plasma Center

Ecole Polytechnique Fédérale de Lausanne-‐

Switzerland

11.10.15 ICFRM 17-‐ Tutorial Session

(2)

Be ware of my plagiarism

•  Everything You Always Wanted to Know About Sex * But Were Afraid to Ask (1972)

•  Director: Woody Allen

(3)

Plan

•  More will come with the talk on DEMO by Dr. R. Wenninger

•  IntroducOon: The energy issue

•  The Physics basis: reacOons and fuels

•  Why fusion is considered as a “disrupOve energy”?

•  Some (not all) issues

•  ITER

•  Technology besides Materials

•  Road map towards a fusion reactor

•  InerOal conﬁnement

•  15 minutes for Q&A: Everything you always wanted to know about fusion reactors, but dare to ask

(4)

Introduction: The energy problem

•  The constraints:

1.  Increase of world population and therefore energy needs: 7.3 billions in 2015 to 8.9 billions by 2050, remaining stable beyond (UN study), coupled with a today inequality in energy access (inverse champagne glass)

2.  Change in energy mix requirement: stronger reliance on electricity for an increasing urban population

3.  Necessity to have “sustainable” energy “Development that meets the needs of the present without compromising the ability of future generations to meet their own needs” ( Brundtland report)

o  Environment aspects: global warming

o  Safety: accidents should not impose population evacuation

o  Legacy towards next generations: depletion of fossil fuels; waste repository on a “human” (not geological) time scale

(5)

Electricity

consumpOon/ capita

•  World bank data (h\p://data.worldbank.org/indicator/

EG.USE.ELEC.KH.PC/countries/all?display=graph)

•  World 3064 kWh/capita

•  EU: 6144 kW/h/ capita; Germany: 7270 kWh/

capita ; Switzerland: 7343 kWh/capita

•  China: 3810 kWh/capita; India: 744 kWh/capita

•  Vietnam: 1273 kWh/capita, HaiO: 50 kWh/

capitaà = 0.007 of Germany

(6)

Fusion reactions

•  Fusion reactions: “Easiest” to achieve reaction:

D + Tà He ( 3.5 MeV) + neutron

(14.1 MeV)

Other reactions

D + D à He³( 0.82 MeV) + neutron

(2.45 MeV

D + D à T ^(1.0MeV)+ H ^{( 3.0MeV)}

D + He³à He⁴ (3.76 MeV) +p ^(14.7MeV)

Energy release E = Δm * c²

2-3

n

Fission products

U

(7)

Fusion cross section

1 keV à T = 10 millions degrees through the relaOon k_BT = E

(8)

Lawson criterion (1)

•  Fusion power release > Power loss

•  Ions have a Maxwellian distribuOon f(E) characterized by a temperature T

•  CalculaOon of the fusion reacOvity <σv> , which is average over the distribuOon funcOon

•  Triple product Density n* Temperature T*Energy conﬁnement Ome τ_E > 5* 10²¹ m^-‐3keV s

(9)

Lawson criterion (1a)

•  Plot of <σv> versus T

(10)

DerivaOon of Lawson

criterion (1)

(11)

DerivaOon of Lawson criterion (2)

(12)

Lawson criterion (2)

•  Q deﬁniOon= Fusion power/ External HeaOng power

•  But the fusion reacOons provide energeOc He ions (3.5 MeV) which can thermalize with the D and T ions (10-‐20 keV): He ions is a source of heaOng

•  Qà inﬁnity (igniOon) if External HeaOng power is null: all needed heaOng is provided by He ions

•  For a reactor, igniOon is not required Q = 30-‐40

(13)

The challenge of fusion

Density n* Temperature T*Energy conﬁnement Ome τ_E > 5*

10²¹ m^-‐3keV s The challenge:

1. To create a plasma with n about 10 ²⁰ m^-‐3 and T about 10⁸K,i.e. 10 keV

2. To conﬁne its energy during τ_E of a few seconds

There are many Ome scale: ParOcle conﬁnement

Ome τ_P, Plasma duraOon, Energy conﬁnement Ome

(14)

Fuel issues

•  D: abundant as natural isotope of H ( 1/7000)

•  T: Short life ( 12.3 years) radioacOve ( β decay at about 5.7 keV)

•  Needs to “ breed” triOum using the neutron from the fusion reacOon D+ T à n + He

6Li + nà T + ⁴He + 4.8 MeV (exothermic)

7Li + nà T + ³He + n – 2.5 MeV (endothermic)

•  Importance for the “Breeding Blanket” in a reactor

(15)

Fuel issues (a)

•  Cross secOon of the fusion reacOon of n and ⁶Li and ^7Li

(16)

Fusion : a

“disruptive” energy

•  Why a “disruptive” energy?

(1)

Li is abundant in the crust and in the sea water ( WEC 2013)

2) No chain reactions; no severe accidents: fuel inside the reactor sufficient only for a few

minutes (no “Tchernobyl” type accident);

(17)

Fusion : a

“disruptive” energy

•  (3) Environmental friendly

(2)

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(18)

Fusion : a

“disruptive” energy

4.  Development of low activation materials ( Cf.

(3)

Talk by A Moeslang and A. Kimura)à no need of geological repository

5.  This contributes as well to the safety aspect by reducing the “after heat”

(19)

11.10.15 ICFRM 17- Tutorial Session

Market penetration

•  Economics studies confirm the possibility for fusion to penetrate the market

0 5 10 15 20 25

base 750 650 550 450

CO2 target (ppm)

Electricity Production (EJe) solar

wind biomass fusion fission gas coal hydro

0 105 1520 2530 35 4045

Coal Gas Nuclear fission Biomass Photovoltaics Wind Fusion

External Costs [mEuro/kWh]

Global Warming Other

Sum

(20)

State of ma\er at T>

10

⁵

K , about 10 eV

•  Binding energy e-‐ion: about 10 eV

•  At fusion temperature, the state of ma\er is

plasma, i.e. a “gas” formed by electrons and ions , globally neutral and dominated by “collecOve”

eﬀect

•  Debye shielding: a charge is surrounded by a cloud of opposite charges which “shield” its Coulombian potenOal V_c. Beyond a few Debye lengths λ_D, V_c is no longer felt. λ_D = (ε₀k_BT/n₀e²)^1/2

(21)

Conﬁnement

•  Due to the Debye screening, electrostaOc conﬁnement is not possible: electric ﬁeld is shielded aqer a few Debye length

•  Two possibiliOes:

u No conﬁnementà InerKal conﬁnement and

realisaOon of the triple product through very high density n ( very short τ_E and τ_P )

u By magneOc ﬁeld à MagneOc conﬁnement

(22)

MagneOc conﬁnement (1)

•  Through the Lorentz force F_lorentz = q(v x B )

•  B is generated either or both current by external coils or by the plasma it self

∇ × B = µ_o ^j

f = Force density in fluid description =ρ_el

(

^j × B

)

(23)

MagneOc conﬁnement (2)

•  Simple toroidal magneOc field (closed field lines) created by a a wire is not sufficient : parOcles

“driq” across magneOc ﬁeld due to curvature and spaOal variaOon (1/r) of B: the driq direcOon

(verOcal) depends on the charge, leading to charge separaOon and hence a verOcal electric ﬁeld E.

This E combined with the B leads to a global driq of both charge species according to (E x B),

leading to loss of conﬁnement

(24)

Tokamak

•  Conﬁnement is provided by a toroidal magneOc ﬁeld B_T provided by external toroidal coils( TF

coils) and by a current carried by the plasma itself I_P.

(25)

Tokamak

(26)

Tokamak ﬁeld lines and

aspect raOo

(27)

T3 (USSR)

1968: 1 keV conﬁrmed by a team of scienOsts from UKAEA ( cold war). It

opens the era of tokamak

(28)

Conﬁnement modes

H mode: High energy

conﬁnement mode

(29)

H à L mode transiOon

(30)

Divertor

Divertor: Where parOcle and energy from the

plasma are removed.

Divertor plate: W

High heat ﬂux material Cf. Talk by Dr. S. Lisgo

(31)

Divertor:

•  54 Divertor cassettes

•  High heat flux components capable of 10MWm^-2 in stationary operation and 20MWm^-2 transiently

CFC

W – ^“reflector plates” DIVERTOR

Divertor (ITER)

Heat load up to 20 MW m^-‐2

(32)

Divertor:

•  54 Divertor cassettes

•  High heat flux components capable of 10MWm^-2 in stationary operation and 20MWm^-2 transiently

CFC

W – ^“reflector plates”

Divertor (ITER)

(33)

Stellarator

•  3D magneOc conﬁnement created exclusively by external magneOc coils. No plasma current: no disrupOon

W7 X stellarator

(34)

HeaOng (1)

•  In the case of a tokamak where we have a plasma current I_P, what is the heaOng by this current?

•  What is the resisOvity of a plasma? In the keV regime, it is like Cu, but it decreases as T^-‐3/2.

•  Ohmic heaOng , taking into account

phenomenological loss rate, cannot bring a

tokamak plasma to the 10-‐20 keV regime. The temperature will be about 4 keV ( Freiberg)

(35)

Heating (2)

•  Heating by absorption RF waves or by injection of fast neutral particles, which thermalize with the plasma particles

RF waves at ion cyclotron frequency( about 50 MHz) or electron cyclotron frequency ( about 150-200 GHz)

Injection of fas t neutral partciles (1 MeV)

(36)

Current drive (1)

•  What is current drive? The toroidal plasma I_P is an essenOal component of a tokamak

I_P is induced as the current in a transformer. So it cannot be

sustained in steady state

(37)

Current drive (2)

•  Non inducOve current drive can be achieved by

injecOon of parOcle momentum ( neutral beam) or by preferenOally injecOng EM waves using

Doppler shiqed resonance e.g. For electron cyclotron wave: ω = Ω_ce +/-‐ k_//v_// or by

manipulaOng the pressure

•  Example of full non inducOve current drive in a medium size tokamak

EX/W-5

2

analysis is performed with eight energy bins available for each chord, with adjustable thresholds within the 10-200 keV range.

The second harmonic X-mode ECE radiometer observes the plasma along one of three possible horizontal viewlines, two on the high field side and one on the low field side, and operates in the 78-114 GHz range with 24 channels of 0.75 GHz bandwidth [6]. The EC radiation observed on the high field side is dominated by relativistically downshifted emission by the high energy end of the electron distribution function and can thus be employed to diagnose the suprathermal population.

The quasilinear Fokker-Planck code CQL3D [7] is employed to model the dynamics of the electron distribution function. The code is coupled to the TORAY-GA ray-tracing module [8] and solves the Fokker-Planck equation in two velocity and one spatial dimensions. The equation in- cludes a quasilinear EC wave damping term, a relativistic collision operator and a model for ra- dial diffusion, with an optional linear dependence on the parallel velocity and a particle- conserving advection term.

2. ECCD and suprathermal electrons

The ability to control the deposition location and toroidal injection angle accurately is instru- mental in the application of ECCD to current profile tailoring. This high degree of control was clearly demonstrated in TCV by sustaining the non-inductive plasma current with two X2 gyrotrons at the time, and firing two sets of two gyrotrons in succession for their maximum pulse durations (2 s). As shown in Fig. 1, the TCV discharge length was thus extended to a record 4.3 s, well beyond the maximum length achievable in Ohmic conditions. Matching the powers, deposition locations and parallel wave numbers of the two sets of beams is essential for a smooth switch-over. This external control was further demonstrated by an interlaced square-wave modulation of the two clusters (180 degrees out of phase), with no visible resulting modulation of the plasma parameters.

500 100

Plasma current (kA)

0 0.5 1 ECRH power cluster A (MW)

0 0.5 1

ECRH power cluster B (MW)

−1 0 Loop voltage (V) 1

6

7 Ohmic transformer current (kA)

1 1.5 Edge elongation

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

1.5

2.5 Internal inductance

Time (s)

FIG. 1. TCV discharge 20881 of record length (4.3 s), sustained by 0.9 MW ECCD.

!

(38)

Physics issues (1)

•  A magneOcally conﬁned plasma contains free energy which can be released as instabiliOes

•  Example: Consider a tokamak as a levitated ringin a magneOc ﬁeld topology. Eanrshaw theorem

indicates that the equilibrium is not stable. One degree of freedom is unstable: in a tokamak it is called the VerOcal Displacement Event VDE,

leading , if uncontrolled to disrupOon

(39)

Physics issues (2)

•  Another example: The conﬁnement of the 3.5 MeV He ions produced by the fusion reacOons

•  These energeOc ions may be lost by interacOon

with waves ( Alfven waves) excited in the plasma, before thermalizing with the D and T ions.

•  Heat removal in divertor

•  …. And many more

(40)

Material science issues

•  A very exciOng ﬁeld to deliver materials which ü  Have the necessary thermo-‐mechanical

properOes under irradiaOon

ü Are compaOble with the operaOon of magneOcally conﬁned plasma

ü Fulﬁl the promises of waste disposal

•  In itself it is an exciOng ﬁeld

(41)

Space

Time

1-30 nm, 1-10 ps

1-5 nm, 2 ps - s 1 nm - 1 µm, 10 ps - s

10 nm - µm, ns - s

10 nm - 10 µm, µs - hours

DDD

kRT

0.1 nm - 1 m, 1 ps - years

MD

Formation energies

of point defects 0.1 nm

Ab Initio

kMC FEM

0 50 100 150

-250 -200 -150 -100 -50 0 50 100

K (MPa m1/2)

T(˚C)

6 2 1

3

4 5

1. RT, unirradiated 2. RT, 0.37 dpa 3. RT, 0.93 dpa 4. 523 K, unirradiated 5. 523 K, 0.30 dpa 6. 523 K, 0.75 dpa 800

700 600 500 400 300 200 100 0

σ [MPa]

10 9 8 7 6 5 4 3 2 1 0

ε[%]

Ttest = Tirrad.

1 µm - 1 cm Kinetic rate

theory

Discrete dislocation dynamics

Finite element modelling

Kinetic Monte Carlo Molecular dynamics

Atomic displacement cascade

Stacking fault

tetrahedron Interaction edge dislocation- void

Nanocrystal

TEM simulated image TEM image

TEM image

TEM image

kRT equations Interaction

dislocations- defects

Tensile tests

Creep tests Fracture toughness versus temperature Bend bar with

FEM mesh

(42)

ITER objectives (1)

•  ITER objectives:

1. Produce P _fusion = 500 (360) MW_th of during 400

(3000) s with an external additional heating P_heating 50 MW (Power gain Q =P _fusion /P_heating = 10)

2. Study physics of a “burning” plasma, i.e. when the energetic 3.5 MeV He nuclei from fusion reactions are confined and provide a dominant heating power (100 MW compared to the 50 MW of external

heating)

(43)

ITER objectives (1)

3.  Integrate in a single device the different

technologies (e.g. superconductivity SC, heating methods and all associated power electronics) and the physics constraints

4. Prove the safety aspects of a fusion reactor: ITER is the first fusion reactor to be licenced as a nuclear

reactor

(44)

Extrapolation for

ITER

(45)

The ITER tokamak

Plasma

Current I_P :15 MA Major radius R= 6.2 m

Plasma radius a = 2m

R/a= 3.1

Fusion power: 500 MW

Pulse : 400s SC Poloidal

field (PF) coils

SC Toroidal field (TF) coils B_T= 5.3 T

SC Central solenoid (CS)

Generates I_P

Ports for Heating &

Current Drive and Diagnostics

R

(46)

ITER safety

•  Aqer the Fukishima accident, ITER also went through the so called “stress test” as any other nuclear reactor

ITER was licenced as “réacteur nucléaire de base”

according to the French nuclear legislaOon in2012, becoming the ﬁrst fusion reactor to be licenced

(47)

Superconductors

•  Coils to create the magneOc conﬁguraOon of ITER are superconducOng (either Nb₃Sn or NbTi)

NB₃Sn condcutors for CS ( leq) and TF (right) coils

(48)

Toroidal field coils (

^ITER)

(49)

Some features of ITER

•  ITER will include Test Blanket Modules TBMs, which are mock-‐ups of Breeding Blanket for a reactor

EU HCLL and HCPB TBM

(50)

TBM

He-Cooled Ceramic Breeder concepts F  proposal to install a specific-design TBM (China, EU, India)

F proposal to contribute with a specific- design sub-module in other Parties TBM (Korea, Japan, RF, USA)

Lithium-Lead concepts

F Helium-Cooled design (EU)

F Dual-Coolant (He+LiPb) design (US, India) F Dual-Functional design, which is initially a HCLL evolving later to DCLL (China)

Water-Cooled Ceramic Breeder concept F specific-design TBM (Japan)

Molten Lithium concepts

F Self-Cooled design (SCLi) (RF)

F He-Cooled design type (HCLi) (Korea)

Solid Breeders Designs Liquid Breeders Designs

TBM

TBMs tests need a whole TBM system

T B M P O R T

(51)

PFC (ITER)

•  CFC divertor targets (~50m²):

−  high thermal conductivity and good

thermal shock resistance (doesn’t melt)

−  but combines chemically with hydrogen (ie tritium)

•  Be first wall (~700m²):

−  good thermal conductivity

−  low-Z_i – low core radiation

−  melting during VDEs

•  W-clad divertor elements (~100m²):

−  high melting point and sputtering resistance

−  but might still melt during thermal transients

−  will eventually replace CFC

(52)

HeaOng and Current Drive in ITER

•  ITER will have 3 methods to heat and perform non inducOve current:

•  Electron cyclotron wave at 170 GHz and 20 MW power deposited to plasma

•  Ion cyclotron wave in the frequency range of 55 MW and 20MW at plasma

•  Neutral beam injecOon at 1 MeV and about 30 A

(53)

Where are we?

•  How far are we from the goal, regarding nTτ_E?

(54)

Another way to ask the quesOon

(courtesy of IO)

•  Electrical power consumpOon to answer the quesOon: Steady state:120 MW conOnuous power consumpOon,180 MVA connected loads (mainly motors), During plasma pulse: 500 MW peak pulse consumpOon, 2.2 GVA connected power converters

(55)

The roadmap towards fusion

•  The roadmap is NOT a single machine but rather a programme:

1.  Build and exploit ITER

2.  A programme on material based on an Early Neutron Source /IFMIF

3.  PreparaOon of DEMO to be operaOonal by 2050 (Cf Talk by Dr. R. Wenninger)

(56)

The Roadmap

Present

experiments +

JET 15 MW_th

ITER

In construction 500 MW_th

DEMO

Preconceptual design

500 MW_e

Fusion

Power Plant

1.5 GW_e

2025-20 30

2050

2015

Man

From Chinese Road map:

DEMO: 2030 FPP: 2050

JET

ENS/IFMIF

(57)

Why do we need a dedicated n source?

•  The fusion reacOons produces neutron with a well deﬁned energy of 14 MeV and hence to test

material one needs a high ﬂux and ﬂuence source close to this energy ( Cf. Dr. J. Knaster talk P9)

§  TransmutaOon; Frenkel pair formaOon; He and H embri\lement (⁵⁶Fe(n,α)⁵³Cr (incident n threshold at 2.9 MeV) and ⁵⁶Fe(n, p)⁵⁶Mn (incident n threshold at 0.9 MeV)

§  InteracOon of the 14 MeV with material (Cf. Dr. A.

Kimura presentaOon)

(58)

InerOal fusion

•  The plasma is NOT conﬁned. Its expansion rate is given by the ion acousOc speed c_s = (k_BT/ Ion

mass)^0.5

(59)

EM wave interacOon with plasma

Interaction zone

InteracOon zone

(60)

The prospect of inertial fusion energy derives from scientific advancements in different arenas

Fast Ignition/Shock Ignition Indirect Drive Laser Fusion:

Central Hot Spot Ignition

Direct Drive Laser Fusion:

Central Hot Spot Ignition

Heavy Ion Fusion

(61)

How ICF could be achieved

(62)

The National Ignition Facility (NIF) provides the

opportunity for ignition physics research at full scale

° ° ° °

Laser Beams (enter through

laser entrance

hole (LEH)

Hohlraum (laser target) Coupling: laser energy couples to

hohlraum and converts to x-rays Drive: x-rays bathe capsule,

heating it up -- it expands

•  conservation of momentum: ablated shell expands outward, rest of shell (frozen DT) is

forced inward

Fusion initiates in a central hot spot and a burn front propagates outward

Fuel DT

Tr (eV)

Symmetry: radiation compresses capsule and it implodes

Time (ns)

(63)

(64)

(65)

NIF laser ampliﬁers

(66)

(67)

The hohlraum

(68)

(69)

(70)

Conclusion (1)

•  Fusion is a mulO generaOon endeavour.

•  To the quesOon : is this worth devoOng your career as a material scienOst?

•  From a personal perspecOve, at the end of my

career , without any regret, I would join again this quest

•  The only thing I would do diﬀerently is to study material sciences, to be able to solve the most challenging ﬁeld of fusion research: a no –no go.

(71)

Conclusion (2)

22^nd World Energy Congress, Daegu 2013

Capturing the Moments

20 November 2013

“The fusion challenge is much bigger than Apollo … It’s like a mission to Mars or jumping from the Wright brothers airplane to the jet engine.” It is generally agreed that the middle of this century is a realisOc Omeline for commercial scale fusion energy, though some it can happen faster.

-‐ Nebojsa Nakicenovic, Deputy Director

& Deputy CEO of IIASA

(72)

but were afraid to ask

Everything you always wanted to know about fusion reactors,