1. 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

2. 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 , 1982

3. 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 , 1996

4. 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 , 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, , 2010

5. 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

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

7. 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)

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

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

10. 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%: %

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

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

13. Thank you very much for your attention Questions?