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Assessment of ECCD-Assisted Operation in DEMO

Explore achievable ECCD efficiency for DEMO options & power needed for fully non-inductive operation. Evaluate ECCD's role in ensuring continuous Tokamak fusion reactor operation.

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Assessment of ECCD-Assisted Operation in DEMO

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  1. Max-Planck-Insititut für Plasmaphysik Assessment of ECCD-Assisted Operation in DEMO Emanuele Poli1, Emiliano Fable1, Giovanni Tardini1, Hartmut Zohm1, Daniela Farina2, Lorenzo Figini2, Nikolai Marushchenko3, Laurie Porte4 (1) Max-Planck-Institut für Plasmaphysik, EURATOM Association, Garching bei München, Germany (2) Istituto di Fisica del Plasma del CNR, EURATOM-ENEA-CNR Association, Milano, Italy (3) Max-Planck-Institut für Plasmaphysik, EURATOM Association, Teilinstitut Greifswald, Germany (4) Centre de Recherches en Physique des Plasmas, CRPP-EPFL, Lausanne, Switzerland Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  2. Motivations • External current drive essential in a tokamak fusion reactor to ensure (nearly) steady-state operation • ECCD usually considered technologically mature, but not very attractive because of comparatively low CD efficiency (driven current per injected power) • However: • Wall-plug efficiency also important for a power plant (might be higher for ECCD) • Smaller slot in the blanket required for ECCD as compared to NBI • Optimization of ECCD efficiency still possible… • In this talk: • Exploration of the achievable ECCD efficiency for 2 DEMO options • First estimate of the ECCD power required for fully non-inductive operation • (loop voltage → 0) Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  3. Current drive efficiency • “Standard” efficiency used for reactor studies: • Typical values quoted for reactor-grade plasmas: Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  4. DEMO models • Global parameters as originally proposed by D. Ward for H & CD assessment • CHEASE equilibria reprocessed by ASTRA (investigate different density and temperature profiles at same βN) • Steady-state DEMO: R0 = 8.5 m, a = 2.83 m, B0 = 5.84 T, βN = 2.95 Density Temperature Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  5. DEMO models • Global parameters as originally proposed by D. Ward for H & CD assessment • CHEASE equilibria reprocessed by ASTRA (investigate different density and temperature profiles at same βN) • Pulsed (6 hrs) DEMO: R0 = 9.6 m, a = 2.4 m, B0 = 7.45 T, βN = 2.6 Density Temperature Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  6. Current drive scenarios • High magnetic field → ordinary mode, first-harmonic heating envisaged • High temperature → significant parasitic absorption by higher harmonics • Resonance condition implies first-harmonic absorption possible if • ECCD modelling (TORBEAM) including momentum conservation (Marushchenko) First-harmonic accessibility (Steady-State DEMO) Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  7. Mid-plane injection, peaked density • Scan over frequency ω/2πand toroidal angle β (poloidal angle = 0) • ICD first rises as the deposition is pushed towards the plasma centre, then decreases because of too large parasitic absorption • High-field side hardly accessible Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  8. Mid-plane injection, peaked density • Scan over frequency ω/2πand toroidal angle β (poloidal angle = 0) • ICD first rises as the deposition is pushed towards the plasma centre, then decreases because of too large parasitic absorption • High-field side hardly accessible Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  9. Mid-plane injection: example • Near maximum current drive: β = 40°, ω/2π = 215 GHz • Second-harmonic absorption ≈ 8% (34% for ω/2π=225 GHz,28% for β=35°) Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  10. Top injection, peaked density, 230 GHz • Injection from R = 10.5 m, Z = 3.5 m to reduce the path through the 2nd-harmonic absorption region • Allows high-efficiency off-axis current • High N|| needed to move the 1st -harmonic region to larger R; more sensitive to injection angle Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  11. Top injection, peaked density • Optimum efficiency shifts towards larger minor radii for higher antenna location • γCD > 0.35 obtained around ρpol ~ 0.2-0.3 Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  12. Top injection, flat density, 230 GHz • Injection from R = 10.5 m, Z = 3.5 m • Higher ECCD current because of lower density as in the “peaked” case, but lower efficiency Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  13. Large-aspect-ratio, pulsed DEMO • Lower trapped-particle fraction, lower Zeff → higher current drive • High frequencies needed because of high magnetic field (290 GHz in this example) Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  14. Power required for steady state • Vanishing loop voltage achieved for deposition around ρpol = 0.4 with approx. 230 MW of injected power (bootstrap fraction around 0.35) Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  15. Summary • High ECCD efficiency possible with careful optimization (largest values around ρpol ~ 0.3) • High-frequency sources necessary • Investigation of self-consistent ECCD-equilibrium loop under way → optimization of CD position in terms of efficiency and bootstrap fraction Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  16. Current drive efficiencies • CD efficiency defined on each flux surface as ratio between current density and deposited power density • Dimensionless efficiency • In terms of total driven current and total absorbed power (apart from geometric factors) • ζCD intended to describe efficiency variations due to changes of the velocity-space region where the wave-particle interaction takes place Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  17. ECCD Modelling • Beam tracing code TORBEAM, linear absorption (TORAY and GRAY fully-relativistic routines), adjoint method for CD (including momentum conservation) • Extensively benchmarked… • Momentum conservation leads to a CD increase Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

  18. Mid-plane injection, peaked density • Scan over frequency ω/2πand toroidal angle β (poloidal angle = 0) • ICD first rises as the deposition is pushed towards the plasma centre, then decreases because of too large parasitic absorption • ζCD ~ γCD/Teincreases due decreasing trapped-particle fraction Emanuele Poli, 17th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012

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