EUROfusion Assessment of Alternative Divertor Solutions for DEMO Holger Reimerdes For the WPDTT1 project In close collaboration with WPPMI, WPPFC and WPDTT2
EUROfusion Assessment of Alternative Divertor Solutions for DEMO H. Reimerdes 1 , L. Aho-Mantila 2 , R. Albanese 3 , R. Ambrosino 3 , W. Arter 4 , S. Brezinsek 5 , H. Bufferand 6 , G. Calabro 7 , G. Ciraolo 6 , D. Coster 8 , H. Fernandes 9 , J. Harrison 4 , I. Kaldre 10 , K. Lackner 8 , O. Lielausis 10 , J. Loureiro 9 , T. Lunt 8 , G. Mazzitelli 7 , S. McIntosh 4 , F. Militello 4 , T. Morgan 11 , N. Pelekasis 12 , G. Pelka 13 , V. Pericoli 7 , V. Philipps 5 , F. Subba 14 , F. Tabares 15 , B. Viola 7 , R. Wenninger 8 , R. Zagorski 13 and H. Zohm 8 1 EPFL-SPC, Lausanne, Switzerland, 2 VTT, Finland, 3 Università di Napoli, Italy, 4 CCFE, Culham, UK, 5 Forschungszentrum Jülich, Germany, 6 CEA, St. Paul-lez-Durance, France, 7 ENEA- Frascati, Italy, 8 Max-Planck-Institut für Plasma Physik, Garching, Germany, 9 Universidade de Lisboa, IST, Portugal, 10 University of Latvia, Latvia, 11 DIFFER, Nieweign, The Netherlands, 12 University of Thessaly, Volos, Greece, 13 IPPLM, Warsaw, Poland, 14 Politecnico di Torino, Italy, 15 Ciemat, Madrid, Spain H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 2
Pursue development of alternative divertor solutions as risk mitigation European roadmap for fusion energy • Identified heat exhaust as the main challenge towards the realisation of magnetic confinement fusion • Assess and develop alternative divertor solutions in case the baseline solution will not extrapolate to DEMO - ITER being the ultimate test of the baseline solution • Extrapolation of alternatives to DEMO based on today’s “proof-of-principle” experiments and modelling considered too large • Consider a dedicated Divertor Tokamak Test (DTT) facility to develop alternative(s) to sufficient maturity for deployment in DEMO H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 3
Outline EUROfusion assessment of alternative divertor solutions for DEMO § Strategy and baseline § Assessment of alternative divertor configurations § Assessment of liquid metal PFCs H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 4
Outline EUROfusion assessment of alternative divertor solutions for DEMO § Strategy and baseline § Assessment of alternative divertor configurations § Assessment of liquid metal PFCs H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 5
Assessment strategy • Focus on solution with high potential to reach sufficient technological maturity in time for a DEMO to start operation in the 2040s • Compare potential “benefits” and “costs” of alternatives with the baseline DEMO solution Ø Produce a short-list of the most promising alternatives H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 6
Compare alternatives with the European baseline divertor solution for DEMO • Conventional DEMO scenario with P elec = 500 MW ( R = 8.8 m, B t = 5.8 T, I P = 20 MA) [Wenninger, Kemp, private communication] - Single null divertor (SND) 2014 DEMO1 (A=3.1) - Tungsten (W) targets P heat,eff ¡= ¡ 300 ¡MW ¡ H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 7
Compare alternatives with the European baseline divertor solution for DEMO • Conventional DEMO scenario with P elec = 500 MW ( R = 8.8 m, B t = 5.8 T, I P = 20 MA) [Wenninger, Kemp, private communication] - Single null divertor (SND) Example.: Water cooled ITER-like - Tungsten (W) targets W monoblock • Target requirements - T e,t < 5 eV to avoid W sputtering - q ⊥ ,t < 5-10 MW/m 2 to avoid target damage [You, et al., EFPW (2014)] H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 8
Compare alternatives with the European baseline divertor solution for DEMO • Conventional DEMO scenario with P elec = 500 MW ( R = 8.8 m, B t = 5.8 T, I P = 20 MA) [Wenninger, Kemp, private communication] - Single null divertor (SND) Example.: Water cooled ITER-like - Tungsten (W) targets W monoblock • Target requirements - T e,t < 5 eV to avoid W sputtering - q ⊥ ,t < 5-10 MW/m 2 to avoid target damage • Assumptions - Power decay length λ q,u ~ ρ pi ~ 3 mm - Min. grazing angle 1.5 Deg ➜ A w = 2 m 2 /target Total radiated Power to outer q ⊥ ,outer,max fraction target (MW) * (MW/m 2 ) P rad /P heat =90% 20 10 P rad /P heat =95% 10 5 [You, et al., EFPW (2014)] *Assume a 1:2 in:out asymmetry H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 9
Compare alternatives with the European baseline divertor solution for DEMO • Conventional DEMO scenario with P elec = 500 MW ( R = 8.8 m, B t = 5.8 T, I P = 20 MA) [Wenninger, Kemp, private communication] - Single null divertor (SND) - Tungsten (W) targets • Target requirements - T e,t < 5 eV to avoid W sputtering - q ⊥ ,t < 5-10 MW/m 2 to avoid target damage Ø Radiate 90-95% of the • Assumptions heating power - Power decay length λ q,u ~ ρ pi ~ 3 mm Ø Reduce SOL pressure to - Min. grazing angle 1.5 Deg ➜ reduce power deposition A w = 2 m 2 /target due to recombination Total radiated Power to outer q ⊥ ,outer,max processes ➜ (partial) fraction target (MW) * (MW/m 2 ) particle detachment P rad /P heat =90% 20 10 P rad /P heat =95% 10 5 *Assume a 1:2 in:out asymmetry H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 10
Extrapolation of baseline solution to DEMO is uncertain Main sources of uncertainty are • Power decay length λ q and wetted area A w • Confinement and its compatibility with high core radiation • Stability of detachment under high heat fluxes • Ability to sufficiently suppress transients H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 11
Alternative divertor concepts can help in two ways Decrease peak heat and particle Increase exhaust capabilities and/or flux onto the divertor target of divertor targets Alternative magnetic divertor Liquid metal target armour configurations Increase divertor energy and In-situ repair of damaged surface momentum losses Easier access to detachment/ Greater tolerance for transients wider operating regime Thinner armour/convection/ More robust/stable detachment evaporation for higher heat handling capability Distribute power over a greater surface H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 12
Outline EUROfusion assessment of alternative divertor solutions for DEMO § Strategy and baseline § Assessment of alternative divertor configurations § Assessment of liquid metal PFCs H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 13
Considered alternative configurations • X divertor (XD) [M. Kotschenreuther, et al., Phys. Plasmas 14 (2007) 72502] - Increase pol. flux expansion to flare flux surfaces towards target • Super-X divertor (SXD) [P.M. Valanju, et al., Phys. Plasmas 16 (2009) 056110] - Increase major radius of target (only way to increase A w at constant γ without invoking plasma physics) - Combine with XD and flare flux surfaces • Snowflake divertor (SFD) [D.D. Ryutov, Phys. Plasmas 14 (2007) 064502] - Second order null point expands flux near null point - In practice always two nearby x-points with SF+ or SF- topology H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 14
Considered alternative configurations Divertor concept* Key characteristic Geometry Effect on power exhaust X divertor (XD) Increase pol. flux Flaring • Stabilise location of detachment front (?) [Kotschenreuther, expansion to flare et al., Phys. flux surfaces Longer connection length/ • Cooler targets ease access to detachment Plasmas 14 (2007) towards target larger SOL volume • Higher volumetric losses ease access to 72502] detachment Lower target tilt • Recycling neutrals reflect upstream for easier detachment (?) Super-X divertor Increase major Increase wetted area • Lower peak heat flux (SXD) [Valanju, et radius of target(s) al., Phys. Plasmas Decrease q || • Cooler targets ease access to detachment 16 (2009) 056110] Introduce gradient in q || • Stabilise location of radiation front (?) Can be combined See XD with an increase of pol. flux expansion Snowflake Second order null Converging flux surfaces • Stabilise location of detachment front (?), divertor (SFD) point - in practice towards target albeit close/within confined plasma [Ryutov, Phys. always two nearby (distinguish SF+ and SF-) Plasmas 14 (2007) x-points with SF+ or Longer connection length/ • Cooler targets ease access to detachment 064502] SF- topology larger SOL volume • Higher volumetric losses ease access to detachment Large low field region and • May affect turbulent transport (?) larger shear • May broaden/narrow the SOL (?) *Not necessarily first incarnation H. Reimerdes | 1 st IAEA TM on Divertor Concepts | Vienna | October 1, 2015 | Page 15
Recommend
More recommend
