Designing the Optimal Fusion Experiment Sophia A

Designing the optimal fusion experiment Sophia A. Henneberg [email protected] Content

• The Max-Planck-Institute for Plasma Physics (IPP) • Motivation for fusion reactors • Background on fusion reaction • Background on plasma & magnetically confined fusion experiments • Tokamaks (including ITER) & stellarators (including W7-X) • Tokamak-Stellarator-Hybrid • Summary

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 2 Max-Planck-Institut für Plasmaphysik (IPP)

• Institute of the Max-Planck-Gesellschaft (MPG) • National research laboratory (Helmholtz-Gemeinschaft) • Located in Garching and Greifswald • 1994: foundation of the Greifswald branch • 2000: completion of building • Staff: approximately 450 people • construction and operation of the fusion experiment W7-X (one of Germany’s biggest research projects)

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 3 Content

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 4 Worldwide primary energy consumption 1800-2017

https://ourworldindata.org/ 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 5 CO2

http://climate.nasa.gov/vital-signs/carbon- dioxide/ http://www.esrl.noaa.gov/gmd/ccgg/trends/ 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 6 Global temperature development

http://data.giss.nasa.gov/gistemp/

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 7 Years of fossil fuel reserves left

Fossil fuel reserves-to-production (R/P) ratios in years

114

50.7 52.8

BP (2016) BP Statistical Review of World Energy 2016 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 8 Future Energy Production

Challenges: • rising energy consumption • secure energy supply

• curbing of global warming (CO2-reduction) • limitations of fossil energy (possible substitute?)

Strategy for minimizing risk: • parallel development of different concepts as part of a future energy supply concept (solar, wind, storage of energy, nuclear fusion, …)

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 9 Fusion as an energy source

D in 4,5 l of water and lithium (6Li) of an old laptop battery can provide energy for a family for 3 years.

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 10 Content

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 11 Nuclear Energy: Fusion or Fission

fission (chain reaction)

fusion (thermonuclear burning)

Energy can be produced by fusion of light nuclei or by fission of heavy nuclei

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 12 Potential Energy in Nuclear Fusion

• potential well: difficult to overcome

• finite probability for tunneling through 360 keV the barrier classical particle

quantum-mechanical particle

• probability highest for light nuclei with tunnel effect high velocity energy ~ 1/r 0

4 x 10-15 m distance between nuclei r Potential Potential

-17.6 MeV small distances: large distances: attraction by nuclear forces repulsion by Coulomb-force

source: R. Kleiber 2014 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 13 Nuclear Fusion in the Sun pp-cycle in the sun p+p → D+e++

D+p → 3He+

solar core: T = 15∙106 K, n = 1026 cm-3

Every second 600 Mio. t of hydrogen are transformed into 596 Mio. t of 3He+3He → 4He+2p helium according to E = mc2. 17 source: A. Kleiber 2014 This yields a power of 3,610 GW. Important: Gravitational force overcomes repulsive forces 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 14 Controlled Nuclear Fusion on Earth

• low cross-section of pp-cycle Fusions reactor • very slow (t = 3·109 a) • very unlikely • long life-time of the stars • not feasible on earth! • more likely reaction: Deuterium-Tritium (DT) • faster than pp-cycle (t = 100 s) • required temperature: approx. 150 Mio K (15 keV)

Sun Proton

Neutron Hydrogen Deuterium Tritium H D T 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 15 Anticipated Fusion Reaction on Earth

Fuels Deuterium (D) • part of seawater (0,15 ‰) D+T → 4He+n Tritium (T) D 4He • can be “bred” from lithium • radioactive (half-life period 12 a) • only small amount in reactor due to breeding 4 Lithium (Li) T n He • contained in rocks (0,05 ‰) Li → resources (D, Li) available for many millenniums T “Ash“ Helium (He) 6 4 Energy n+ Li → T+ He n+7Li → T+4He+n kinetic energy of neutrons → heat

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 16 Triple Product (Lawson Criterion )

▪ neutrons leave the plasma -> power generation ▪ -particles confined -> heating

▪ heating:

▪ loss due to radiation: ▪ loss due to transport: (diffusion, turbulence)

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 17 Ways to confine a plasma

source: Sfan00_IMG, Layout of the National Ignition Facility. Image taken from a LLNL publication, en.wikipedia, 2010.

source: IPP, 1997

Die Sonne mit Protuberanzen am 12. März 2013 um 13.19 UT; source: SOHO, ESA & NASA (EIT 304).

gravitation (stars)

source: IPP, 1998 source: Damien Jemison/LLNL, 2012 magnetic confinement inertial fusion

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 18 Content

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 19 Plasma

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 20 Magnetic mirror

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 21 From magnetic mirrors towards a torus

• Magnetic mirrors • confinement perpendicular to axis • but: particles lost at the ends • closing the field toroidally • quasi-endless configuration • but: particle losses due to drift motion (reason: inhomogenous field and curvature)

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 22 Particle Trajectories without Rotational Transform

Plasma particles leave the torus.

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 23 Twisted Field Lines (Rotational Transform)

Twisted magnetic fields lead to better confinement of particles.

• two field components

• Bt toroidal field • Bp poloidal field give rotational transform • creation of magnetic flux surfaces source: R. Kleiber, A. Pulss 2008 • rotational transform varies over radius

two possible concepts to generate rotational transform: Tokamak & Stellarator

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 24 Particle Trajectories with Rotational Transform

Plasma particles are confined to the torus.

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 25 Tokamak (тороидальная камера с магнитными катушками)

developed around 1950 by Artsimovich and Sacharov in Moscow: + intrinsic heating + most advanced fusion concept – no stationary operation (works like a transformer) current drive – current quench possible (disruption)

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 26 Tokamak experiments world-wide

KSTAR Daejon (KR) ASDEX Upgrade Garching (D) JET Culham (GB)

ITER Cadarache (F) EAST Chengdu (C) DIIID JT-60SA San Diego (USA) Naka (JA)

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 27 ASDEX-Upgrade

R = 1.65 m a = 0.5 m  = 1.6

Bt  3.5 T Ip  1.4 MA PH  28 MW

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 28 Joint European Torus (JET), Culham, Great Britain

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 29 ITER

• final report: 2001 • site: CEA Cadarache • start of construction: 2009 • first plasma: 2025 • first fusion: 2035 • The purpose of ITER is to show the scientific and technological feasibility of fusion power. basic specifications R [m] 6.2 a [m] 2.0

TPuls [s] 300 PFusion [MW] 500 power gain (Q) 10 cost [G€] 20 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 30 Stellarators

Figure 8-stellarator: first Stellarator designed by Lyman Spitzer at Princeton Plasma Physics Laboratory (PPPL)

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 31 Classical Stellarator

+ external currents only − complex three-dimensional geometry + good controllability − reflected particles not confined + stationary operation  need and potential for optimization

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 32 Why we can optimize stellarators

• 3D shapes open up very large design space: ~ 40 independent parameters (A. Boozer, L. P Ku, 2010) based on SVD analysis • Axisymmetric tokamak shape parameters: e, k, d • Thought experiment: quantize shape parameters into 10 levels • 103 2D configurations vs. 1040 3D configurations => “combinatorial explosion” • Other large numbers: 7x1022 visible stars, 6x1030 prokaryotes (bacteria) on earth’s surface

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 33 Stellarator optimization

criteria met? coil coil system ▪ magnetic surfaces ▪ small Shafranov-shift Yes ▪ MHD-stability ▪ small neoclassical transport ▪ small bootstrap current ▪ confinement of α-particles ▪ technically feasible coils

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 34 Stellarator optimization

• Simons Foundation grant (2019) • "Hidden Symmetries" • New designs and/or methods to be expected very shortly

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 35 Optimized stellarators confine the particles well

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 36 Wendelstein 7-X: optimized stellarator

plasma cross section

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 37 Wendelstein 7-X: optimized stellarator

plasma cross section

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 38 Nine years in three minutes

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 39 Goals of the Wendelstein 7-X Project

• confirm: • feasibility (coil system) • successful optimization • long-pulse operation (suitability for power plant) • extensive research programme: • transport of plasma and impurities • efficiency of non-ohmic heating (ECRH, ICRH, NBI) • control of boundary layer plasmas (divertor) • verification of numerical models W7-X is an experiment and will not produce any energy (HH and HD plasmas only) Do stellarators play a role for future power plants?

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 40 Comparison Tokamaks vs Stellarators

Tokamaks (2D, with plasma current) Stellarators (3D, no plasma current)

+ good insulation/confinement - Bad insulation/confinement (not exact + toroidal symmetry symmetry only quasi-symmetry) - Pulsed operation (transformer!) - More complex coils - current-driven instabilities + continuous operation + no current-driven instabilities

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 41 Tokamak-Stellarator-Hybrid: Quasi-axisymmetry (QA)

• The magnetic field strength is nearly independent of the toroidal coordinate: B≈퐵(푠,휃). This reduces the radial drift of particles. • Because of the toroidal symmetry of the magnetic field strength, QA-configurations share many properties of tokamaks, such as high intrinsic current.

NCSX ESTELL 휃

푁휑 Beidler et al Nucl. Fusion 51 076001 (2011) Drevlak et al. Contrib. Plasma Phys., 53, (2013) 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 42 Tokamak-Stellarator-Hybrid : Quasi-axisymmetry (QA) What are potential benefits of a quasi-axisymmetric configuration? • Avoidance of disruptions: There is experimental evidence that compared to vacuum rotational transform stabilizes certain types of disruptions (CTH, W7-A: [2] Bartlett et al., Nuclear Fusion, 20, (1980)). tokamaks

NCSX ESTELL 휃

푁휑 Beidler et al Nucl. Fusion 51 076001 (2011) Drevlak et al. Contrib. Plasma Phys., 53, (2013) 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 43 Disruption avoidance – e.g. CTH CTH: Compact Toroidal Hybrid

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment CTH: Maurer, ISHW Greifswald 2015 44 Tokamak-Stellarator-Hybrid : Quasi-axisymmetry (QA) What are potential benefits of a quasi-axisymmetric configuration? • Avoidance of disruptions: There is experimental evidence that compared to vacuum rotational transform stabilizes certain types of disruptions tokamaks (CTH, W7-A: [2] Bartlett et al., Nuclear Fusion, 20, (1980)). • Steady state: Since it potentially does not need much externally driven current. compared to • Reduced transport other stellarators • Compact: High intrinsic current fraction could potentially simplify coil design and make a more compact device possible.

NCSX ESTELL 휃

푁휑 Beidler et al Nucl. Fusion 51 076001 (2011) Drevlak et al. Contrib. Plasma Phys., 53, (2013) 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 45 Quasi-axisymmetric designs

• First quasi-axisymmetric equilibria were presented in 1994 by Nührenberg, Lotz and Gori (Theory of Fusion Plasmas Varenna, page 3, (1994)) and then in 1996 by Garabedian (Physics of Plasmas, 3, 2483 (1996))

• Several others have followed, e.g. o CHS-qa (Okamura et al., Nuclear Fusion (2001)) o Which led to CFQS (Shimizu A et al, Plasma Fusion Res. (2018)) o ESTELL (Drevlak et al. Contribu. Plasma Phys., (2013)) o NCSX (Neilson et al., Fusion Engineering and Design, (2003); Neilson et al., IAEA-CN-94/IC1) • R/a=4.4, R=1.4m, N=3, B=1.2-1.7T, Rotational transform=0.39…0.65, 훽 < 4%

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 46 Finding more advanced quasi-axisymmetric designs

Can we find configurations which improve on these previous studies?:

❑ Compact design (aspect ratio R/a of 3 to 4)

❑ Small fast-particle loss rates to provide fusion-relevant knowledge

❑ MHD stable

Henneberg, et al., Nucl. Fusion, 59, (2019) 026014 Henneberg et al., submitted to PPCF, 2019

29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 47 Open problems

Tokamaks Materials and Technology • Advanced operational scenarios, i.e. • divertor materials: high heat fluxes (>10 current drive MW/m2) • Suppression of disruptions • wall materials: fatigue caused by strong • Control of edge localized plasma bursts neutron flux (ELMs): 10 GW/ m2 for ITER • robotic maintenance technology Stellarators (remote handling) • Suitability of stellarators for power Fuel Cycle generation • development of blanket technology • Impurtiy transport and confinement of • breeding ratio of 1.1 -1.15 required α-particles • implementation of Tritium cycle Tokamak-Stellarator Hybrids • exhaust of helium ash • Can we really combine advantages? 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 48 Summary

• Nuclear fusion is a virtually inexhaustible source of energy. • Nuclear fusion is achieved in sufficiently hot and dense plasmas. • Magnetic confinement is an approach to utilise fusion energy. • Experiments explore the potential of both tokamaks and stellarators. • W7-X is an optimized stellarator designed for operation with long pulses. • ITER is expected to be the first machine generating excess power • Stellarator design space is huge so improved designs can be found, i.e. quasi- axisymmetric designs

Knotatron 29th Oct. 2019 -- MPP S. Henneberg -- Designing the optimal fusion experiment 49