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Recent work on impurity transport at JET

Recent work on impurity transport at JET. P.Mantica on behalf of TFT impurity transport group. Two main issues explored - Z dependence of D and v - use of RF to control impurity accumulation. Experimental Z dependence. C.Giroud, IAEA 2006. Z dependence predicted by GS2. C.Giroud, IAEA 2006.

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Recent work on impurity transport at JET

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  1. Recent work on impurity transport at JET P.Mantica on behalf of TFT impurity transport group

  2. Two main issues explored- Z dependence of D and v- use of RF to control impurity accumulation

  3. Experimental Z dependence C.Giroud, IAEA 2006

  4. Z dependence predicted by GS2 C.Giroud, IAEA 2006

  5. 2006 experiments • A wide dataset of He, Ar/Ne, Ni (Mo) injections has been collected throughout campaigns • Main topics: • Collisionality scan 0.03<n*<0.3 • Beta scan 1.2<bN<2 • Comparison H-mode/hybrid • Comparison H-mode/L-mode • Effect of RF • Role of q profile • Impurity accumulation in ITBs Data analysis still largely to be carried out

  6. Effect of RF Past results have clearly shown that RF in electron heating reduces heavy impurity accumulation

  7. Impurity pinches Reduction of impurity accumulation with RF electron heating ascribed to parallel velocity pinch reversal due to R/LTe driven TEM

  8. 2006 experiments Role of RF electron heating in controlling Ni accumulation fully confirmed The effect of electron heating RF power on Ni (A=28) profiles has been studied at ITER like collisionality in JET H-mode and Hybrid discharges via Laser Blow Off Preliminar outcome: • The peaking factor (–v/D ) decreases with RF power (i.e. Ni density profiles change from peaked to hollow) • The effect is similar in Hybrid and H-Mode discharges • Hollow profiles with RF power found also for Mo (A=42) Role of power deposition profile yet to be verified

  9. The method for the analysis • Two codes used at JET for transport analysis : Mattioli’s and UTC/Sanco • Benchmarking of the two for Ni analysis in a L-mode discharge gave comparable results • Both 1-D codes work out D’s and v’ of the selected impurities by iteratively solving the transport equations till general spectroscopic data from the experiment (emission lines , CXRS data and energy integrated SXR lines of sight – 2 cameras) are matched.

  10. Peakingfactor of Ni versus RF power PRELIMINARY 69808 68671 58149 and 59143 (RF in MC on 3He - Rdep ~ 3.2) 68383 RF in MH on H Rdep=0. 66432-34 (RF in MC on 3He - Rdep ~ 3.2)

  11. Ni profiles: STATIONARY CONDITIONS Peaked 68671, H- mode NO RF 66434 Hybrid 2.1 MA/3.34 T 20 MW NBI, 2 MW RF Mode Conversion Flat/hollow 66432 H-mode 2.1 MA/3.34 T 20 MW NBI, 2 MW RF Mode Conversion

  12. The hypothesis for the cause for the metals profile flattening with RF heating is still the parallel compressibility pinch reversal due to R/LTe driven TEM . Modelling with GS2 still to be done.

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