MaxPlanckInsititut fr Plasmaphysik Assessment of ECCDAssisted Operation in

Max-Planck-Insititut für Plasmaphysik Assessment of ECCD-Assisted Operation in DEMO Emanuele Poli 1, Emiliano Fable 1, Giovanni Tardini 1, Hartmut Zohm 1, Daniela Farina 2, Lorenzo Figini 2, Nikolai Marushchenko 3, Laurie Porte 4 (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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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

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: R 0 = 8. 5 m, a = 2. 83 m, B 0 = 5. 84 T, βN = 2. 95 Density Temperature Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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: R 0 = 9. 6 m, a = 2. 4 m, B 0 = 7. 45 T, βN = 2. 6 Density Temperature Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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

Mid-plane injection, peaked density § Scan over frequency ω/2π and 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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

Mid-plane injection, peaked density § Scan over frequency ω/2π and 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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

Top injection, peaked density, 230 GHz § Injection from R = 10. 5 m, Z = 3. 5 m to reduce the path through the 2 nd-harmonic absorption region § Allows high-efficiency off-axis current § High N|| needed to move the 1 st -harmonic region to larger R; more sensitive to injection angle Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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 velocityspace region where the wave-particle interaction takes place Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,

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

Mid-plane injection, peaked density § Scan over frequency ω/2π and 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/Te increases due decreasing trapped-particle fraction Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7 -10,