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

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

Assessment of ECCD-Assisted Operation Assessment of ECCD-Assisted Operation in DEMOin 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

Max-Planck-Insititut für Plasmaphysik

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)

Current drive efficiency “Standard” efficiency used for reactor studies:

Typical values quoted for reactor-grade plasmas:

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

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

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)

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

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°)

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

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

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

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)

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)

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

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

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

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, 2012 Assessment of...

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