Automatic Analysis of Edge Pedestal Gradient Degradation during ELMs S. González, J. Vega, A. Murari, A. Pereira and JET-EFDA contributors 7th Workshop on Fusion Data Processing, Validation and Analysis, March 2012

Introduction (I) H-mode features [1]: Improved particle confinement Existence of an External Transport Barrier (ETB) Existence of Edge Localised Modes (ELMs) [1] F. Wagner et al., Regime of improved confinement and high beta in neutral-beam-heated divertor discharges of the ASDEX tokamak, Physical Review Letters 49 (19), pages 1408-1412, 1982

Introduction (II) ELMs [2]: Instabilities at the plasma edge H-mode plasmas At each burst: The ETB is reduced The plasma confinement degrades Quantify the edge pedestal gradient degradation during ELMs [2] H. Zohm, Edge localized modes (ELMs), Plasma Physics and Controlled Fusion 38, pages 105-128, 1996

Edge Pedestal Gradient (I): ELMs location UMEL [4] Dα peaks Diamagnetic energy drops Automatic [3] S. González, J. Vega, A. Murari, A. Pereira, M. Beurskens and JET-EDA contributors, Automatic ELM location in JET using a Universal Multi-Event Locator, Fusion Science and Technology 58 (3), pages 755-762, 2010 [4] J. Vega, A. Murari, S. González and JET-EFDA contributors, A universal supprt vector machines based method for automatic event location in waveforms and video-movies: applications to massive nuclear fusion databases, Review of Scientific Instruments 81, 023505, 2010

Edge Pedestal Gradient (II): ET, SGT and SGB At each instant, two signals are considered: Electron Temperature (ET) profile Steep Gradient Temperature (SGT): difference of temperature between two consecutive radial points of ET Steep Gradient Baseline (SGB): mean value of the SGT between the plasma core and the ETB

Edge Pedestal Gradient (III): ET, SGT and SGB JET pulse 78072: L & H temperature profiles comparison a) b)

Edge Pedestal Gradient (IV): ELMs analysis SGTETB For each ELM burst: SGT is compared at two different times: At the ELM time (ELM) 2 ms before (ELM-0.002) SGT is measure at the ETB At the ELM time (SGTETBELM ) 2 ms before ( SGTETBELM-0.002)

Edge pedestal gradient (V): degradation ELM-0.002 ELM SGTETBELM-0.002 SGTETBELM

Edge Pedestal Gradient (VI): example ELM-0.002 ELM SGTETBELM-0.002 SGTETBELM

Edge Pedestal Gradient degradation results: Results (I) Edge Pedestal Gradient degradation results: # pulses analysed: 409 # ELMs analysed: 22486 Edge pedestal gradient degradation mean value: 33.98% # ELMs, degradation higher than 80%: 924, 4.11% # ELMs, degradation higher than 90%: 291 1.29%

Edge Pedestal Gradient (VII): evolution Edge Pedestal Gradient 2ms after the ELM Pulse 789072, time = 8.9951 s Mean degradation: 17.34 %

(degradation = 0 not shown, 6380 ELMs) Results (II) Distribution of the edge pedestal gradient degradation of analysed ELMs Degradation between ELM time -0.002 and ELM time+0.002 Mean Value: 17.34% (degradation = 0 not shown, 6380 ELMs) Degradation between ELM time -0.002 and ELM time Mean Value: 33.98%

Thank you very much for your attention Questions?