Power Exhaust – Walls – Materials for Tokamaks Marco Wischmeier Max-Planck-Institut für Plasmaphysik 85748 Garching marco.wischmeier at ipp.mpg.de Joint ICTP-IAEA College on Advanced Plasma Physics, Triest, Italy, 2016 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 1
ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 2
Goal of magnetic confinement research Goal of magnetic confinement research Neutrons leave plasma into power conversion system è will be used for net energy production D + T → He + n + 17.6 MeV 14.1MeV ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 3
Goal of magnetic confinement research He heats plasma è needs to be exhausted D + T → He + n + 17.6 MeV 3.5MeV 14.1MeV Used for net energy production ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 4
Losses perpendicular to magnetic field Losses perpendicular to magnetic field Turbulent transport dominates Device of R>7m should ignite Turbulence From DIII-D Gene code www.ipp.mpg.de Device of R>7m should ignite /~fsj/gene/ ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 5
Fusion exhaust must… Fusion exhaust must… v Maximize pumping of He ash v Provide sufficient pumping of hydrogen fuel v Minimize damages to the wall (erosion, melting) ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 6
Divertor concept Divertor concept Maximize pumping of He ash and minimize erosion Confined plasma Scrape-Off Layer plasma ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 7
Divertor concept Divertor concept Confined plasma Scrape-Off Layer plasma UPSTREAM TARGET ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 8
Divertor & Plasma Divertor & Plasma P heat in centre From JET ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 9
Divertor & Plasma Divertor & Plasma Distributed Recycling particles From JET ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 10
Divertor & Plasma Divertor & Plasma 10 8 K 10keV From JET ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 11
Divertor & Plasma Divertor & Plasma 10 8 K 10 keV Thin Scrape Off Layer 10000 K 1 eV From JET ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 12
Width of Scrape-Off Layer? What is the power flux? ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 13
Measuring power deposition profile Measuring power deposition profile Infrared image of target T. Eich PSI 2012 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 14
The power decay length The power decay length λ q H-mode (reduced turbulent transport ) T. Eich PRL (2011), T. Eich IAEA FEC 2012, A. Scarabosio PSI 2012 No dependence on machine size R ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 15
What is the power flux density in the SOL? ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 16
Importance of Importance of tokamak tokamak size R size R DEMO ASDEX JET (EU) ITER Upgrade (IPP) 6.2 m >7 m 3 m Major Radius 1.65 m ~ 100 MW ~ 600 MW ~ 38 MW P heat 23 MW Good energy confinement è large R (P fus ~R 3 – see yesterday) ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 17
P/R as figure of merit P/R as figure of merit A measure of the severity of the heat flux is M. Kotschenreuter et al. NF 50 2010 • P heat /R K. Lackner Comm. PPCFusion 15 1994 Device P heat /R q || upstream JET 7 20 GW/m 2 ASDEX 14 35 GW/m 2 Upgrade ITER 20 50 GW/m 2 DEMO 80-100 >300 GW/m 2 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 18
What are the limitations imposed by wall materials? ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 19
Erosion limits maximum Temperature Erosion limits maximum Temperature Ions accelerated to energies ~ Z x 3.5 x T e in electrical field by sheath potential Erosion yields W has low Yield ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 20
Tritium retention Tritium retention J. Roth, K. Schmid, Phys Scripta 2011 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 21
All tungsten plasma facing components All tungsten plasma facing components in ASDEX Upgrade in ASDEX Upgrade 2012 R. Neu PSI 2012 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 22
Technological limits under neutron Technological limits under neutron irradiation irradiation Integrated approach: Combination of coolant, structural material of coolant pipe and armour material? Water cooled divertor segment E.U. protoype monoblock 10MW/m 2 to 5MW/m 2 is the technological limit ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 23
ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 24
ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 25
Liquid metals as Plasma Facing Risk mitigation: Liquid metals as PFC Components D. N. Ruzic et al. NF 2011 V. A. Evtikhin et al. PPCF 2002 NSTX H. W. Kugel et al. Fusion Eng. and Des. 2012 A. G. McLean et al. JNM 2013 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 26
Liquid metals as Plasma Facing Risk mitigation: Liquid metals as PFC Components D. N. Ruzic et al. NF 2011 V. A. Evtikhin et al. PPCF 2002 NSTX H. W. Kugel et al. Fusion Eng. and Des. 2012 A. G. McLean et al. JNM 2013 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 27
How can we reduce the power load onto the divertor target plates to match the technological limit? ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 28
How can we reduce the power load onto the divertor target plates to match the technological limit? 1. GEOMETRY ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 29
Magnetic Flux Expansion Magnetic Flux Expansion R. Pitts et al., TCV, (CH), PSI 2000 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 30
Target inclination Target inclination R. Chodura 1984 Impact angles of 1.5 – 3.5 degrees Courtesy H. Meyer, MAST ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 31
Power load reduced by geometry Power load reduced by geometry Device P heat /R q || upstream q target (geometry) JET 7 20 GW/m 2 20 MW/m 2 ASDEX Upgrade 14 35 GW/m 2 35 MW/m 2 ITER 20 50 GW/m 2 50 MW/m 2 DEMO 80-100 >300 GW/m 2 300 MW/m 2 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 32
Increase of divertor major R Numerical simulations of DEMO device : SONIC Ø With long leg – Target at larger R: Ø Lower q || and larger A wet (here compensated by lower f) N. Asakura et al. NF 2014 Ø Lower core radiation required Ø Lower core dilution N. Asakura et al. P1-103 at PSI2014 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 33
Risk mitigation: Risk mitigation: Advanced divertor configurations (I) Advanced divertor configurations (I) TCV (CH): Snowflake NSTX (USA): Snowflake ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 34
Risk mitigation (II): a (Super-) X divertor M. Kotschenreuther et al. arXiv:1309.5289 Second X-point è low poloidal B Caveat of high flux expansion and thus potentially too low impact angles on target plate à but Super-X may reduce issue Super-X concept: Valanju et al. Phys. Plasmas 16, 056110 (2009) ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 35
Advanced divertor configurations (III) Advanced divertor configurations (III) MAST Super-X (UK) E. Havlickova et al., JNM 2013 E. Havlickova et al., PET 2013 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 36
How can we reduce the power load onto the divertor target plates to match the technological limit? 2. Basic SOL Physics ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 37
Divertor Regimes: high recycling Divertor Regimes: high recycling Total plasma pressure is constant along magnetic field line P e + P i + dynamic pressure = constant Temperature gradient P SOL ≈ conducted Γ SOL upstream target è High recycling regime: low T e (< 5eV), high n e è Satisfactory for existing tokamaks è VERY HIGH PARTICLE FLUXES ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 38
Do we need to limit the particle flux? Do we need to limit the particle flux? Neglecting power loads on PFCs from radiation è Total power = (8T + 15.8 ) 1.602 10 -19 Γ [W] ; T e = T i = T [eV] Power across sheath Surface recombination of D + to D 2 ICTP Trieste College on Advanced Plasma Physics M. Wischmeier 39
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