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Moving fast in fusion reactors: ASCOT – race track for fast ions

Moving fast in fusion reactors: ASCOT – race track for fast ions. T. Kurki-Suonio, Aalto University for the ASCOT team O. Asunta, E. Hirvijoki, T. Koskela, J. Miettunen S. Sipilä, A. Snicker and S. Äkäslompolo. MeV–range ions in reactors  MW/m2 on the wall?. Today’s tokamaks

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Moving fast in fusion reactors: ASCOT – race track for fast ions

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  1. Moving fast in fusion reactors: ASCOT – race track for fast ions T. Kurki-Suonio, Aalto University for the ASCOT team O. Asunta, E. Hirvijoki, T. Koskela, J. Miettunen S. Sipilä, A. Snicker and S. Äkäslompolo

  2. MeV–range ions in reactors MW/m2 on the wall? Today’s tokamaks • only mock-fuel: pure D  ”no” fusion reactions Tomorrow’s reactors: • Fusion reactions  3.5 MeV alphas • Neutral beams  1 MeV deuterons and/or tritons • ICRH heating  ions with several MeV

  3. How to confine hot ions so that― they heat the plasma― they do not destroy the wall? In principle, charged particles are glued to the magnetic field lines

  4. But life is never so simple... Fast ions can have large gyro radii and ENORMOUS banana widths

  5. Engineering reality: no axisymmetry An almost ideal situation: JET w/ 32 coils Reactor reality: ITER w/ 18 coils Only finite # of TF coils  B-field becomes a ”toroidal sausage” = Toroidal Field Ripple

  6. ITER reality:There is more to life than the TF ripple... Even the harmonic ripple structure is destroyed by things like • Presence of ferritic material in the walls • Ferritic inserts (FI) reduce the TF ripple • Ferritic structures can introduce strong local perturbations. Prime example: TBMs in ITER • Also by lack of FIs (around NBI ports) • External coils can generate their own ’ripples’ at their will. • Prime example: ELM-mitigation coils in ITER (and, today, at AUG, DIII-D, JET)

  7. Example: BT (φ) at the edge of ITER Toroidal ripple 0.25%, Field bump due to NBI ports 0.57% Field bump due to TBMs 1,1%

  8. How to study fast ions today: DT-experiments to produce 3.5MeV alphas? • few and far apart: • TFTR (1993): Pfus = 10.6 MW • JET (1997): Pfus = 16.1 MW (Q ~ 0.7) Externally produced fast ions? • Neutral beam injection: only up to about 100keV • ICRH: MeV range ions but only few  We are left at the mercy of simulations • Multitude of codes, but one appears quite far ahead of the others...

  9. ASCOT Fully 3D • 3D magnetic field • 3D Wall Realistic orbit tracing • Guiding center (fast) • gyro orbit (accurate) Comprehensive interactions • Coulomb collisions • Turbulent transport • Models for relevant MHD: • NTM-type magnetic islands • Alfven Eigenmodes

  10. Some examples: 3D effects on fast ions a la ASCOT • TBM mock-up experiments at DIII-D • Effect on NBI-ions • Effect on neutrons from DD -> DT -fusion reactions • The effect of ELM-mitigation coils on wall loads: • NBI-ions in ASDEX Upgrade • ITER wall power loads due to fusion alphas: • The effect of ripple & Co • The effect of wall structure

  11. The effect of ferritic structures Case Study: TBM mock-up experiments @ DIII-D

  12. NBI-generated deuterons in DIII-D discharges w/ TBM mock-up limiters TBM mock-up coils

  13. DD  DT  14 MeV n M. Schaffer & al, Nucl. Fusion 51 (2011) 103028 Experimental neutron flux in the TBM mock-up exp’t Fraction of confined tritium in the plasma as calculated by ASCOT

  14. The effect of ELM-mitigation Coils Case study: B-coils in ASDEX Upgrade

  15. Losses of 60keV NBI deuterons Direct ripple well losses Additional spot next to the coil

  16. Fusion alphas in ITER Advanced Scenario-4 Ip = 9MA ’only’  Confined fast ions vulnerable

  17. Axisymmetry vs ripple vs FI2-limiter case Axisymmetric B-field With ’nude’ ripple Ripple w/ FI’s

  18. Original wall w/ 2 limiters Present wall design w/ poloidally extended ’continuous’ limiters Also wall shape matters...

  19. Future of fast stuff: full of work! • F4E task approved: • GRT-379: “Calculation of the TBM-induced ripple in ITER, wall loads, impact on plasma and optimization”, 2012 – 2014; 777 500 € • ITPA-EP activity: expert group twice a year • Tritium experiments at JET (2015?)

  20. Thank you for your attention!

  21. Acknowledgements • For input data: • ITER Organization, IPP Garching, General Atomics • For computing resources: • The supercomputing resources of CSC – IT center for science • HPC-FF • For funding: • This work was partially funded by the Academy of Finland Projects No. 121371 and No. 134924 • This work, supported by the European Communities under the contract of Association between Euratom/Tekes, was carried out within the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

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