Carine Giroud 1 21st IAEA Fusion Energy, Chengdu Carine Giroud 1 IAEA, Chengdu Progress in understanding impurity transport at JET C. Giroud 1, C. Angioni 2, G. Bonheure 3, I. Coffey 4, N. Dubuit 5, X. Garbet 5, R. Guirlet 5, P. Mantica 6, V. Naulin 7, M.E. Puiatti 8, M. Valisa 8, A.D. Whiteford 9, K-D. Zastrow 1, M.N.A. Beurskens 1, M. Brix 1, E. de la Luna 10, K. Lawson 1, L. Lauro-Taroni 8, A. Meigs 1, M. O’Mullane 9, T. Parisot 5, C. Perez von Thun 1, O. Zimmermann 11 and the JET-EFDA Contributors

Carine Giroud 2 21st IAEA Fusion Energy, Chengdu Within ITB region: Transport can be close to neoclassical predictions Rest plasma region Inward velocity V~Vneo Impurity D >> Dneo Iter physics group NF 99 Inside core region W accumulation observed with peaked density profile without central wave heating in ASDEX Global observation: plasma with peaked density are prone to accumulation of highly charged impurities Picture of impurity transport in present devices

Carine Giroud 3 21st IAEA Fusion Energy, Chengdu Content Observation of anomalous impurity transport at JET – Reduction of Nickel peaking by electron heating Brief description of recent development in the turbulent transport theory Comparison of experiment with theoretical predictions – A transition of the dominant instability driving the transport could explain the difference in Nickel peaking – Experimental test of Z dependence predicted by turbulent transport theory

Carine Giroud 4 21st IAEA Fusion Energy, Chengdu Linear relationship assumed between impurity flux and density gradient In steady-state conditions and with edge source the local impurity density gradient length: Experimental determination of transport coefficients Diffusion coefficient Convection coefficient Vz >0 outwards Peaking factor R major radius device

Carine Giroud 5 21st IAEA Fusion Energy, Chengdu Experimental determination of transport coefficients Intrinsic impurities such as C: direct measurement of density profile – measured density gradient determines –RV/D Extrinsic impurities injected by laser ablation (Ni) or gas injection (Ne, Ar). − D and V determined individually by modelling of time evolution of spectroscopic data − Ni: soft x-ray and VUV − Ne and Ar: soft x-ray and VUV and also from charge exchange spectroscopy

Carine Giroud 6 21st IAEA Fusion Energy, Chengdu Effect of electron heating on Ni transport #58144, dominant ion #58149, dominant electron Two similar ELMy H-modes: Two heating schemes: Different gradient lengths: [M-E. Puiatti PoP ] q 0 >1 0.1 < eff <0.2 (low collisionality) Bt=3.28T, q95=5.9, 3MW ICRH, 12-14MW NBI ICRH dominant ion heating: 8 % 3 He ICRH dominant electron heating: 20% 3 He Density gradient length R/Ln Te gradient length R/LTe Temperature ratio Te/Ti Ti gradient length R/LTi

Carine Giroud 7 21st IAEA Fusion Energy, Chengdu Two very different Ni profiles ICRH dominant ion heating Peaked Ni profile ICRH dominant electron Slightly hollow Ni profile [M-E. Puiatti PoP ] Steady-state profile calculated from D and V

Carine Giroud 8 21st IAEA Fusion Energy, Chengdu Due to change in Ni transport [M-E. Puiatti PoP ] – Diffusion increased in centre – Convection reversed at mid-radius While neoclassical transport unchanged  Reduction in Ni peaking due to anomalous transport Neoclassical x10 ICRH dominant ion heating ICRH dominant electron heating Measurement

Carine Giroud 9 21st IAEA Fusion Energy, Chengdu Recent development in turbulent transport theory Two main electrostatic micro-instability considered ITG/TEM Microinstability Ion temperature gradient ITG Trapped electron mode TEM Direction of propagation Ion diamagnetic Electron diamagnetic Destabilised byR/LTiR/LTe & R/Ln

Carine Giroud 10 21st IAEA Fusion Energy, Chengdu Recent development in turbulent transport theory Three main mechanisms have been identified Curvature pinch 1 Compressibility of ExB drift velocity Independent on Z and A Thermodiffusion pinch 2 Compression of the diamagnetic drift velocity Dependent of 1/Z Pinch connected to the parallel dynamics of the impurity 3 Compression of parallel velocity fluctuations produced along the field line by the fluctuating electrostatic potential Dependent on Z/A 2 [X. Garbet PoP ] 2,3 [C. Angioni C PRL ] 1 [J. Weiland NF ] 1 [X. Garbet PRL ] 1 [M. B. Isichenko PRL 1996] 1 [D.R. Baker PoP ] 1 [V. Naulin Phys Rev. E 2005] 2 [M. Frojdh NF ]

Carine Giroud 11 21st IAEA Fusion Energy, Chengdu Pinch mechanisms in theory of turbulent impurity transport All contribute to the total turbulent pinch propagation: ITG ion diamagnetic direction TEM electron diamagnetic direction

Carine Giroud 12 21st IAEA Fusion Energy, Chengdu Illustration of complex Z dependence of turbulent transport D and V calculated with the linear version of the gyrokinetic code GS2: - trace impurity considered. - only the fastest growing mode is taken in the quasi–linear model - no neoclassical transport included. Complex trend in Z of turbulent transport  specific calculation needed for studied discharge GS2 [R/LTi=7, R/LTe=6, Te/Ti=0.88] [C. Angioni]

Carine Giroud 13 21st IAEA Fusion Energy, Chengdu Peaked Ni profile ICRH dominant ion Slightly hollow Ni profile ICRH dominant electron [M-E. Puiatti PoP ] R/Ln=3.9 R/LTe=4 Te/Ti=0.95 R/LTi=6.6 R/Ln=5.2 R/LTe=6. Te/Ti=1. R/LTi=6.6 Different dominant instability for peaked and flat Ni density ITG dominatedTEM dominated GS2 Steady-state profile calculated from D and V

Carine Giroud 14 21st IAEA Fusion Energy, Chengdu Ni pinch reversal found for a ITG to R/L Te driven TEM transition [C. Angioni PRL ] [M-E. Puiatti PoP ] Investigate transition from ITG to R/LTe driven TEM – Stabilised R/Ln driven TEM: R/Ln=2. – gradually decreasing R/L Ti towards stabilisation of ITG modes. Reproduce a pinch reversal as observed experimentally Real frequency of most unstable mode (c s /R) ITG TEM V<0 V>0 Te/Ti=0.95, R/Ln=2

Carine Giroud 15 21st IAEA Fusion Energy, Chengdu First results on measured Z dependence of impurity peaking #66134 Neoclassic measure- ment measure- ment Neoclassic r/a =0.15 r/a =0.55 Negative C peaking Hollow profile Peaking lower than neoclassical Stronger Z dependence of peaking in core than at mid-radius Ne, Ar and Ni injected in ELMy H-mode q0>1, 0.1 < eff <0.2 Bt=2.9T, q95=7, 2MW ICRH, 8.6MW NBI

Carine Giroud 16 21st IAEA Fusion Energy, Chengdu GS2 peaking in same range as measurements GS2 Anomalous part: -R(V-Vneo)/(D-Dneo) GS2 w/o Thermodiffusion Discharge ITG dominated R/LTi~5.8, R/LTe~6.3, R/Ln~0.3 and Te/Ti~1.1, *~0.10 GS2 Measurement Neoclassic

Carine Giroud 17 21st IAEA Fusion Energy, Chengdu Summary JET experiments confirm earlier observations that neoclassical transport is not sufficient to describe impurity transport in bulk plasma First comparison between turbulent impurity transport theory and experiments show encouraging results: − A transition in the dominant instability driving the transport could explain the observed reversal of Ni convection − Same range of peaking as calculated by linear gyrokinetic calculation are measured : no strong increase of V/D as a function of Z.  Turbulent transport could give the means for controlling heavy impurity peaking in ITER JET is set out to systematically compare theoretical predictions with experiment in coming campaign using JET upgraded CXRS capability..

Carine Giroud 18 21st IAEA Fusion Energy, Chengdu Spare slides

Carine Giroud 19 21st IAEA Fusion Energy, Chengdu Reduction of Ni peaking calculated with linear GS2 Condition for discharge with peaked Ni densities For increasing R/Ln and R/LTe – reduction of peaking calculated Condition for discharge with flat Ni densities Transition from ITG to R/Ln driven TEM Reduction of the pinch predicted but no reversal of the pinch [M-E. Puiatti PoP 2006]

Carine Giroud 20 21st IAEA Fusion Energy, Chengdu LBO Data : inverted SXR emissivity profiles. slower penetration and more peaked profiles MC MH time [s]  

Carine Giroud 21 21st IAEA Fusion Energy, Chengdu Simulation: line & SXR brightnessess MH MC norm. brightness Solid: experimental; dashed:simulation (core) (edge ) (core) (edge )

Carine Giroud 22 21st IAEA Fusion Energy, Chengdu Effect of electron heating on Ni transport Pions (MW.m-3) #58144 #58149 two similar discharges – q0>1 – low collisionality 0.1 < eff <0.2 – 2 ICRH heating schemes were applied dominant ion heating: 8 % 3 He conc. dominant electron heating: 20% 3 He Bt=3.28T, q95=?, 3MW ICRH, 12-14MW NBI Ni transport probed