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Observation of Strong Inward Heat Transport In Tore Supra with Off-Axis ECRH

Observation of Strong Inward Heat Transport In Tore Supra with Off-Axis ECRH. S.D. Song, X.L. ZOU, G. Giruzzi. CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. Motivation. Electron thermal transport: one of the key issues in plasma controlled fusion Empirically divided into two parts:

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Observation of Strong Inward Heat Transport In Tore Supra with Off-Axis ECRH

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  1. Observation of Strong Inward Heat Transport In Tore Supra with Off-Axis ECRH S.D. Song, X.L. ZOU, G. Giruzzi CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France

  2. Motivation • 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?

  3. 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. Methodology (2/2) • 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)

  5. Experimental Layout Ip A1 A2 t • 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 ρdep~0.5, width~3cm - Output Power: A1~300KW; A2~270KW • Diagnostics ECE (32 channels) Reflectometry

  6. Experimental Results 2) Low density : 1) High density:

  7. Experimental Results 2) Low density 1) High density

  8. 2D Image of DTe 1) High density 2) Low density Sawteeth Magnetic Axis Sawteeth Magnetic Axis ECRH Deposition ECRH Deposition Strong inward heat transport

  9. Fourier Analysis 1) High density (40504) 2) Low density (43234)

  10. Density Effect Fundamental harmonic is strongly affected, while higher ones are not affected.

  11. Simulation with Heat Pinch • The electron energy transport equation for plasma electrons with temperature Te and density necan be written in the form • Simplified heat transport equation Source Convection Damping Diffusion • Diffusivity : • Damping time : • Convective velocity:

  12. Sensitivity with k and V 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.

  13. Sensitivity with b (1/tDamp) Minimum of the phase : very sensitive to the damping time, less sensitive to the diffusivity and the pinch.

  14. Pinch Model Simulation Good agreement for all harmonics using pinch model.

  15. 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 Te perturbation transport: Figure from (F. Imbeaux PPCF 2001) 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.

  16. CGM Simulation (1) When simulating the higher harmonic, the lower harmonic disagree. κ=3; λ=2; β=1; α=1.5

  17. CGM Simulation (2) When simulating the lower harmonic, the higher harmonic disagree. κ=3; λ=1; β=1; α=1.5;

  18. Particle Transport Barrier ECRH modulation, TS#40500, density modulation 25 20 15 Amplitude (A.U.) 10 5 0 2 1.5 Phase (rad) 1 0.5 0 2.7 2.8 2.9 3 3.1 3.2 3.3 R (m) • Particle tansport barrier driven by ECRH ? ECRH (rdep=2.82 m) D2=0.3 m2/s V2=-1.2m/s Particle Source pITB (r=2.85 m) D1=0.03 m2/s V1=0

  19. 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 barrierlocated close to the ECRH deposition,

  20. Pinch Model Comparison Without pinch: With pinch:

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