Hacquin, S.

Heuraux, S.

Hornung, G.

Sabot, R.

Sun, Yan

Verdoolaege, Geert

Ghent University Academic Bibliography

 Are spectra evolutions related to a change of turbulence regime? Conclusion Systematic study of broadband turbulence properties in Ohmic, ICRH and LH plasmas Y. Sun1,2,3, R. Sabot1, S. Heuraux2, X. Garbet1, G. Verdoolaege3,4, S. Hacquin1,5, G. Hornung3  1 CEA, IRFM, F-13108 Saint Paul-lez-Durance, France 2 IJL UMR 7198 CNRS, Université de Lorraine, F-54000 Nancy, France  3 Department of Applied Physics, Ghent University, 9000 Gent, Belgium 4 LPP-ERM/KMS, B-1000 Brussels, Belgium 5 EUROfusion Programme Management Unit, Culham Science Centre, Culham, OX14 3DB, UK INTRODUCTION Radial profiles of spectrum characteristics  Modification of the reflectometry spectra is induced by a change of the turbulent regimes.  The spectrum characteristics (magnitude, width, shape) could thus be used as a new tool to determine the dominating micro-instabilities in the transport study. The reflectometry spectra can be decomposed in several components [1]. To perform systematic studies, a parametrization method was developed to fit each component [2]: Spectrum =  Direct current  +  Low frequency  +   Broadband  +    Noise level                                                Two Gaussians             +   Taylor  function  [3]  +  Const.                                                                                   (or generalized Gaussian)  References  For ICRH, 𝐸𝐵𝐵 reaches high level (>0.5) even at low 𝑃𝐼𝐶𝑅𝐻   and the basin disappears at high 𝑃𝐼𝐶𝑅𝐻, whereas the basin remains for LH even at high Power.  The huge differences on BB component (>5 times in the basin) between ICRH and LH are difficult to explain by a different fluctuation level in the two heating methods [1] V.A. Vershkov et al, Nucl. Fusion 45, S203–S226 (2005) [2] Y. Sun, R. Sabot, G. Hornung, S. Heuraux, S. Hacquin, and G. Verdoolaege, Rev. Sci. Instrum. 89, 073504 (2018) [3] P. Hennequin et al., in 26th EPS Conf. on Contr. Fusion and Plasma, Vol. 23J (1999) pp. 977 – 980 [4] R. Sabot et al, Plasma Phys. Control. Fusion 48, B421–B432 (2006) [5] H. Arnichand et al, Nucl. Fusion 54, 123017 (2014)  [6] C. Angioni et al, Phys. Plasmas, Vol. 10, No. 8 (2003) [7] C Bourdelle, Plasma Phys. Control. Fusion 47, A317–A326 (2005) [8] J Citrin et al, Plasma Phys. Control. Fusion 59, 064010 (2017) Explanation One typical density fluctuation spectrum from fixed-frequency reflectometry   A turbulence database contains 350,000 acquisitions from 6,000 Tore Supra shots, excluding the spectra with strong (>50 kHz) Doppler effect or low (<25 dB) SNR.  The spectrum characteristics pave the way to extract general trends from the database.  Arnichand 2016 PPCF  A drop “basin” appears inside the q=1 surface.  The width of this basin scales with the q=1 position  This extends results obtained on dedicated shots in [4]  The radial profiles of the 𝐸𝐵𝐵 median value is obtained  by averaging over d𝜌 = ±0.05. Pure ICRH Pure LH Transition from TEM to ITG has been shown to induce the disappearance of the Quasi-Coherent component in the reflectometry spectra [5].  Could this transition induce a change of the spectra in other components ?  The TEM/ITG stability regime can be related to the effective collisionality 𝜈eff = 𝜈𝑒𝑖/𝜔𝐷𝑒, where 𝜈𝑒𝑖 is the electron-ion collision frequency and  𝜔𝐷𝑒 the curvature drift frequency [6].   For TEM/ITG, a approximation of 𝜈eff is expressed as [6]:  𝜈eff~0.1 R𝑍eff𝑛𝑒𝑇𝑒−2 (𝑛𝑒 in 1019𝑚−3, 𝑇𝑒 in keV)  The similar transition occurs in L-mode with ICRH/LH, reflecting the TEM/ITG transition.   Peaking factor evolution with 𝜈eff supports the interpretation of a fluctuation spectrum evolution related to a transition from TEM to ITG dominated turbulence. Ohmic L-mode  Simulations [8] have shown that density fluctuation spectra are narrower in TEM than in ITG.   Moreover in TEM, the spectra exhibits a LF component  In ITG, this LF component is integrated in the wide BB component.  To systematically investigate the evolution of spectrum characteristics, the normalized broadband contribution is defined as:  EBB = BBdFTotal power of spectrum≈ BBdF BBdF +  LFdF (0 < 𝐸𝐵𝐵<1)  The basin is observed in LOC and SOC regimes in all 𝑞𝜓 range.   In the basin, but also at all positions 𝐸𝐵𝐵𝑆𝑂𝐶 > 𝐸𝐵𝐵𝐿𝑂𝐶  higher fluctuations in SOC than in LOC To study the difference between LOC & SOC regimes, a LOC/SOC empirical threshold was obtained from Tore Supra (𝑁𝑙, tE) database:  𝑵𝑳𝑶𝑺/𝑺𝑶𝑪 𝟏𝟎𝟏𝟗𝐦−𝟐 ≈ 𝟐. 𝟔 × 𝑰𝒑 𝐌𝐀 .   The LOC/SOC transition ( 0.9~1.1 𝑁𝐿𝑂𝑆/𝑆𝑂𝐶 )  occurs when  𝜈eff  ∼ 0.4 for the all 𝑞𝜓.  𝐸𝐵𝐵 is low before the LOC/SOC transition then 𝐸𝐵𝐵 increases with 𝜈eff. Spectrum evolutions seem to be related to TEM/ITG transition The peaking factor has been connected to the TEM/ITG transition through the turbulent pinch velocity. The thermodiffusion term is directed outwards when TEM dominates and inwards when ITG dominates [7]. Ohmic L-mode  Radial profiles of 𝑬𝑩𝑩 in L-mode with additional heating Evolution of spectrum characteristics (𝐸𝐵𝐵, width 𝑊𝐵𝐵 ,shape 𝛽𝐵𝐵) agrees with the change of the spectra observed in the simulation.  Radial profiles of 𝑬𝑩𝑩 in Ohmic 

Systematic study of broadband turbulence properties in Ohmic, ICRH and LH sawteeth plasmas

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Systematic study of broadband turbulence properties in Ohmic, ICRH and LH sawteeth plasmas

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