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ITPA – CDBM – Pedestal H-mode t hreshold database status October 2007 - Naka

ITPA – CDBM – Pedestal H-mode t hreshold database status October 2007 - Naka. Yves Martin Centre de Recherches en Physique des Plasmas Association Euratom - Confédération Suisse Ecole Polytechnique Fédérale de Lausanne (EPFL) CH - 1015 Lausanne, S witzerland. Outline. Background

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ITPA – CDBM – Pedestal H-mode t hreshold database status October 2007 - Naka

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  1. ITPA – CDBM – Pedestal H-mode threshold database statusOctober 2007 - Naka Yves Martin Centre de Recherches en Physique des Plasmas Association Euratom - Confédération Suisse Ecole Polytechnique Fédérale de Lausanne (EPFL) CH - 1015 Lausanne, Switzerland

  2. Outline • Background • Research axes • Current status • Current development • Future work

  3. Threshold DB • Threshold DB initiated in 1992 • 5 tokamaks (ASDEX, DIII-D, JET, JFT-2M, PBX-M) • 2200 time slices in L-mode, at the LH transition, in H-mode • 124 variables • Threshold DB in 2007 • 14 tokamaks (Alcator C-Mod, ASDEX, ASDEX Upgrade, CHS, Compass-D, DIII-D, JET, JFT-2M, JT-60U, MAST, NSTX, PBX-M, TCV, TUMAN-3M) • 7700 time slices in L-mode, at the LH transition, in H-mode • ~200 variables

  4. Research axes • Threshold power: estimation of global power law scaling • Variables • In terms of ne, BT, a, R or ne, BT, S • In terms of additional parameters (k, d, e, gaps, Zeff, ...) • Data selection • On large dataset (encompassing all devices, relaxed selection criteria) • On ITER like plasmas dataset • Statistical tools • with Ordinary Least Square log-lin regression fits • with Error in Variable Othogonal Regression, ... • Discriminant analysis (all global DBs) • Other features in the DB • Threshold density, hysteresis, ELM type transitions, ... • Off DB work • Joint experiments (CDB-10, ...)

  5. Current status • Recommended scaling: • Pthresh = 0.049 n0.717+/-0.035 B0.803+/-0.032 S0.941+/-0.019 • Prediction for ITER: • At low density (0.5 x 1020m-3), in DD plasmas: • 52MW (28-96MW) • At high density (1.0 x 1020m-3), in DD plasmas: • 86MW (46-160MW) • Conclusion • Access to H-mode at low density is highly probable at low density with the available 73MW. • At high density more marginal. • Scenario should rely on hysteresis to maintain the plasma in H-mode during density ramp

  6. Current development • Density dependence • Analysis of DB for individual devices at well populated magnetic field values • Conclusion • On might see a small increase in the density dependence with plasma size and magnetic field • Other effects much stronger, such as divertor geometry

  7. Current development • Density of minimum threshold power • relaxed selected data • Find minimum threshold • Take average density • Increases with plasma size. Not an issue for ITER.

  8. Under development – future work • Effect of aspect ratio on threshold power • Including MAST, NSTX, CHS • Hysteresis • At what extent can we rely on hysteresis? • Generally, not 'used' so far (Except in Alcator C-Mod) • Experiments keeping additional power close to the threshold after the L-H transition • Access to good confinement regime (H~1) • Required power above threshold (power ratio) • Most devices show power ratio>1.5 • Few discharges close to threshold in H-mode confinement DB • Scenario ?

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