1. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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 Max-Planck-Insititut für Plasmaphysik

2. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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)

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

4. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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 β N )  Steady-state DEMO: R 0 = 8.5 m, a = 2.83 m, B 0 = 5.84 T, β N = 2.95 DensityTemperature

5. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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 β N )  Pulsed (6 hrs) DEMO: R 0 = 9.6 m, a = 2.4 m, B 0 = 7.45 T, β N = 2.6 DensityTemperature

6. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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)

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

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

9. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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°)

10. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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

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

12. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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

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

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

15. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 Summary  High ECCD efficiency possible with careful optimization (largest values around ρ pol ~ 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

16. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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)  ζ CD intended to describe efficiency variations due to changes of the velocity- space region where the wave-particle interaction takes place

17. Emanuele Poli, 17 th Joint Workshop on ECE and ECRH Deurne, May 7-10, 2012 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

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