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Analysis and preliminary results about the propagation and QL absorption of LH in ITER Sc4

Analysis and preliminary results about the propagation and QL absorption of LH in ITER Sc4. Alessandro Cardinali Associazione Euratom-ENEA sulla Fusione, C.P. 65 - I-00044 - Frascati, Rome, Italy. Main characteristics of the LH applied on the ITER plasma scenarii.

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Analysis and preliminary results about the propagation and QL absorption of LH in ITER Sc4

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  1. Analysis and preliminary results about the propagation and QL absorption of LH in ITER Sc4 Alessandro Cardinali Associazione Euratom-ENEA sulla Fusione, C.P. 65 - I-00044 - Frascati, Rome, Italy

  2. Main characteristics of the LH applied on the ITER plasma scenarii • In ITER plasmas, the application of the Lower Hybrid presents some new features with respect to the previous, which makes the experiment challenging. This, essentially because the plasma parameters and configurations are atypical for this kind of experiment. In particular the ITER plasma are characterized by • High and flat density >1020 m-3 • High temperatures >>10 keV • The presence of non-Maxwellian ion distribution functions (alpha and NBI ions) • Steep density gradients near the separatrix • Very high coupled LH power

  3. Need of a careful analysis of the coupling, propagation and absorption of the LH • In particular we are aware of the following problematic • The possibility that a so high density at the plasma edge, and a so high delivered power level can be responsible of some non-linear phenomena at the plasma periphery that leads to a modification of the LH coupled power spectrum calculated with the Brambilla’s linear theory. • The possibility that at the plasma separatrix where the density gradient is so high, the LH propagation based on the WKB expansions of the Maxwell equations breaks down. • The possibility that owing to the presence of the non-Maxwellian ion components the power will be coupled and dispersed on the ions species instead of electrons.

  4. ITER plasma Sc4 • The goal of the application of the LH to the Sc4 (Steady State Operation) at the ITER plasma is: • Fully non inductive current drive in combination with • Bootstrap current • NBI • Localized off-axis current generation for controlling • Saw-teeth • Neoclassical tearing mode • Optimizing reversed shear for improved access to advanced tokamak regimes. • Previous estimate (Progress in the ITER Physics Basis) • h=0.24-0.30X1020 AW-1 m-2 • r=0.6-0.7 • ILHCD=1.6-2 MA • Rtoplasma=20-30MW

  5. The ENEA-Frascati’s simulation tools • Our simulation tool consists of three modules • PDI-star code • To study the effect of the edge density and power level on the nominal LH spectrum broadening. • RAY-star code§ • To study the propagation of the spectrum from the edge to the plasma core (based on the ray-tracing technique). • FPQL-star code§ • To study the quasi-linear absorption of the spectrum (based on the numerical solution in 2D velocity space of the Fokker-Planck equation). • With the addition of a Full-Wave(1D) module to study the local violation of the WKB approximation. • FULLH-star code • The modules are able to read (and eventually interpolate) externally furnished profiles of magnetic field structure (Grad-Shafranov solver), density and temperature in the bulk and in the SOL. § Note that the last two modules can work also as a single module, and the calculation of the propagation and quasi-linear absorption is iteratively obtained.

  6. Some results of the ray tracing alone (module 1) ITER Sc4trajectories and profiles

  7. Some results of the ray tracing alone (module 1) ITER Sc4damping rate; Linear Power Deposition Profiles & n|| variation

  8. Some results of the ray tracing + Fokker-Planck (module 1&2) ITER Sc4current density profiles with broadened spectrum and nominal spectrum, with LH rays starting from equatorial and off equatorial position

  9. Parametric studies to be performed • Accurate model of the scrape-off plasma to establish the validity of the WKB assumption, in the pedestal zone (module RAY-star). Eventually study of the density transition by the full wave code (module FULLH-star). • On this basis, scan on the density at the edge to establish the possible broadening of the spectrum (module PDI-star). • Study of the quasi-linear absorption, current drive and deposition layer on the basis of the points established before (RAY-star + FPQL-star modules). In particular as function of the • Coupled power (quasi-linear diffusion coefficient Dql) • Width of the spectrum

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