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

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 1

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 2

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. 3

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 4

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. 5

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

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

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 8

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 9

10. Addenda to the results presented the 6th of July 2009 at the CEA Cadarache

11. Some results of the ray tracing alone (module 1) ITER Sc4equilibrium, trajectories, density and temperature profiles

12. Some results of the ray tracing alone (module 1) ITER Sc4equilibrium, trajectories, density and temperature profiles

13. 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

14. Some non-definitive conclusion from the quasilinear analysis • In the case of nominal spectrum we have that 0.7 MA are generated by 7MW of absorbed power, the peak of the current density profile is around r=0.65. • In the case of large spectrum we have that 1MA is generated by 15MW of absorbed power. The peak of the density profile remains around r=0.65; the width extends up to r=0.9 (where is localized another smaller peak) (to be introduced the calculated broad spectrum by PDI). • In the case of linear deposition profile the peak of the profile is localized at r=0.7. This is consistent within this approximation! • Necessary a deeper analysis of the generated current, the layer of deposition, vs the coupled power and various spectra.

15. Work to be done in next days (after 20-23 oct 2009) • Scenario 4 • Equilibrium, density and temperature profiles as given by the transport code (CRONOS or others ask to FI) at the time of LH injection! (done) • Insert too, the SOL profiles (as the most probable) coming from the edge plasma physics modeling. (to be done) • Insert the spectrum which comes from the coupling code (ask to LP and the POLITO) (to be done) • Insert the spectrum which comes from the PDI detailed analysis (ask to RC, CC and AC) (to be done) • Scenario 2 • Repeat exactly the same procedure as before (to be done) • Other request???

16. Serpilli specialistic PHD thesis on LH for ITER • The PHD thesis should be concern a “Parametric study of the LH applied to ITER by using LH-ray tracing coupled to 1D and 2D FP module”: the parametric study should focus on • Determination of the layer of power deposition • Determination of the power absorbed and current generated • Determination of the CD efficiency • As function of the quasi-linear diffusion coefficient strength (coupled power) with the same nominal spectrum (coming from the coupling code calculation) • As function of the power present, by PDI, in the high n|| tail of the spectrum (coming from PDI analysis) • As function of the extension of the n|| tail with the same level of power present in the n|| tail of the spectrum (coming from PDI analysis) This parametric study must concern the SC4 scenario with fixed profiles of density, temperatures in the bulk and in the SOL.