1 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Observation of Strong Inward Heat Transport In Tore Supra with Off-Axis ECRH S.D. Song, X.L. ZOU, G. Giruzzi CEA, IRFM, F Saint-Paul-lez-Durance, France

2 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Electron thermal transport: one of the key issues in plasma controlled fusion Empirically divided into two parts: - Diffusion: proportional to the temperature gradient. - Convection: proportional to the temperature. Heat pinch in tokamaks : a controversy. Actual pinch or ‘pseudo’ pinch? How to separate the convection and the diffusion ? Previous heat pinch experiments with ECRH: DIII-D [T.C. Luce, 1992], RTP [P. Mantica 2000], ASDEX-U [P. Mantica 2006], FTU [A. Jacchia 2002] with different conclusions. On Tore Supra? Motivation

3 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Methodology (1/2)  Power balance method (no separation between diffusion and convection)  Temperature perturbation method (possible separation between diffusion and convection)  Modulation of the heat source Transport coefficients are directly determined from the amplitude and phase of the harmonics of the Fourier transform of the temperature perturbation. In slab geometry, we have:  ECRH modulation Localized and pure electron heating.

4 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou  Previous ECRH modulation experiments Frequency ranging from 30Hz to 300Hz  Tore Supra ECRH modulation experiments Low frequency : 1Hz  Advantages of Low frequency > High amplitude (S/N); > Many harmonics (1st to 11th); > Less affected by sawteeth and other perturbations; > More sensitive to the pinch.  Disadvatages > Transport coefficient varying along with the heat pulse > Additional parameter: Damping time (losses) Methodology (2/2)

5 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Experimental Layout Plasma D plasma; R=2.43m; a=0.7m; Ip=0.7MA; Bt=3.7T. ECRH - Gyrotron frequency: 118GHz - Injection angle Gyrotron A1(high): Φtor=0° Φpol=-7.5° Gyrotron A2(middle): Φtor=0° Φpol=0° - Deposition: off-axis heating with ρ dep ~0.5, width~3cm - Output Power: A1~300KW; A2~270KW Diagnostics ECE (32 channels) Reflectometry A1 A2 Ip t

6 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Experimental Results 1) High density: 2) Low density :

7 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Experimental Results 1) High density 2) Low density

8 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou 2D Image of  T e ECRH Deposition 1) High density 2) Low density Strong inward heat transport Magnetic Axis Sawteeth Magnetic Axis Sawteeth ECRH Deposition

9 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Fourier Analysis 1) High density (40504) 2) Low density (43234)

10 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Density Effect Fundamental harmonic is strongly affected, while higher ones are not affected.

11 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou The electron energy transport equation for plasma electrons with temperature T e and density n e can be written in the form Simplified heat transport equation Simulation with Heat Pinch Diffusion ConvectionDamping Source  Diffusivity :  Damping time :  Convective velocity:

12 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Derivative of the phase : very sensitive to the diffusivity, less sensitive to the pinch and the damping time. Amplitude : sensitive to the diffusivity, very sensitive to the pinch for low harmonics, and not sensitive to the pinch for high harmonics. Sensitivity with  and V

13 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Sensitivity with b (1/  Damp ) Minimum of the phase : very sensitive to the damping time, less sensitive to the diffusivity and the pinch.

14 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Pinch Model Simulation Good agreement for all harmonics using pinch model.

15 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou CGM model CGM (Critical Gradient Model) (F. Imbeaux PPCF 2001,X. Garbet PPCF 2004)  semi-empirical  pure diffusive  threshold  stiffness Effective pinch (or ‘pseudo’ pinch) can be derived for T e perturbation transport: The key point here is whether the pinch observed in the experiments is effective pinch, e.g. CGM derived effective pinch, or a real one. Simulation with CGM have been done to simulate the experimental results. Figure from (F. Imbeaux PPCF 2001)

16 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou CGM Simulation (1) κ=3; λ=2; β=1; α=1.5 When simulating the higher harmonic, the lower harmonic disagree.

17 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou CGM Simulation (2) κ=3; λ=1; β=1; α=1.5; When simulating the lower harmonic, the higher harmonic disagree.

18 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Amplitude (A.U.) ECRH modulation, TS#40500, density modulation R (m) Phase (rad) Particle Transport Barrier ECRH (r dep =2.82 m) D 2 =0.3 m 2 /s V 2 =-1.2m/s D 1 =0.03 m 2 /s V 1 =0 pITB (r=2.85 m)  Particle tansport barrier driven by ECRH ? Particle Source

19 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Conclusions Strong inward heat transport phenomenon has been observed in off-axis ECRH modulation experiments in Tore supra for low density. Simulation using pinch model shows a good agreement for all harmonics. Simulation using CGM cannot fully interpret the experimental results. If higher harmonic agrees, lower ones disagree; and the same for the other way round. Observation of a particle transport barrier located close to the ECRH deposition,

20 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou

21 Association Euratom-CEA TORE SUPRA EAST, China 7 th Jan 2010 X.L. Zou Pinch Model Comparison With pinch: Without pinch: