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# 27th IAEA Fusion Energy Conference - IAEA CN-258

22-27 October 2018
Mahatma Mandir Conference Centre
Asia/Kolkata timezone
CONFERENCE MATERIAL NOW AVAILABLE!

## Role of the pressure position on the pedestal stability in AUG, JET-ILW and TCV in deuterium and hydrogen plasmas and implications for ITER

26 Oct 2018, 14:00
4h 45m
Mahatma Mandir Conference Centre

Poster

### Speaker

Lorenzo Frassinetti (KTH, Royal Institute of Technology)

### Description

The role of the pedestal pressure position ($p_e^{pos}$) in the pedestal stability has been recently highlighted in deuterium (D) plasmas in AUG [1], where it was shown that an outward shift of the pressure can lead to a reduction in pedestal pressure height ($p^{ped}$). The work emphasized the role of scrape-off layer conditions and possibly separatrix density ($n_e^{sep}$) in the global confinement. Instead, the role of $p_e^{pos}$ in JET-ILW has been, so far, elusive [2]. To achieve reliable pedestal predictions for ITER it is necessary to clarify several points: - Do AUG and JET behave in a similar way in terms of the pressure position? - Does the pressure position play a role in the pedestal stability in JET? - Is the variation of $p_e^{pos}$ a general behaviour or is unique to metal wall machines? - What is the role of $n_e^{sep}$? - Does the isotope species influence these mechanisms? These questions are addressed in five steps, by (i) investigating the behavior of the pedestal structure in gas and power scans of unseeded plasmas in AUG, JET-ILW and TCV, (ii) by studying the corresponding physics mechanisms using the P-B model, (iii) by comparing the results with the self-consistent EUROPED code [3]. Further insight into the physics mechanisms are obtained by (iv) non-linear resistive MHD simulations with JOREK and (v) micro-instability analysis with GS2. When the pedestal is P-B limited, similar behaviors are observed in all three devices. The increasing fueling leads to the pedestal degradation. This is explained by the outward shift of the pedestal postion, as verified with EUROPED. A preliminary modelling suggests that the ITER pedestal can be affected by 7-8%. However, this might be an underestimation, as also $n_e^{sep}$ plays an important [1]. EPED overestimates by 25% the experimental $p^{ped}$ in the high $n_e^{sep}$ case. The reason for the discrepancy is investigated with JOREK, to assess the role of resistivity, non-linear MHD and diamagnetic effects and with GS2, to assess the role of micro-instabilities. [1] Dunne M., PPCF 59, 014017 (2017) [2] Stefanikova E., accepted in Nucl. Fusion. [3] Saarelma S., PPCF 60, 014042 (2018)
Country or International Organization Sweden EX/P8-22

### Primary author

Lorenzo Frassinetti (KTH, Royal Institute of Technology)

### Co-authors

Dr Antoine Merle (Ecole Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas (CRPP), CH-1015 Lausanne, Switzerland) Dr BENOIT LABIT (Swiss Plasma Center (SPC) EPFL SWITZERLAND) Colin Roach (Culham Centre for Fusion Energy) Dr Costanza Maggi (CCFE) Dr Elena de la Luna (CIEMAT) Dr Elisabeth Wolfrum (Max Planck Institut fuer Plasmaphysik) Mrs Estera Stefanikova (KTH) Dr Hendrik Meyer (UK Atomic Energy Authority) Dr Jon Hillesheim (Culham Centre for Fusion Energy) Mr Laszlo Horvath (York Plasma Institute, Department of Physics, University of York, York, YO10 5DD, UK) Dr Luis Guimarais (Instituto de Plasmas e Fusão Nuclear, Universidade de Lisboa) Dr Matthias Bernert (Max-Planck-Institut für Plasmaphysik, Garching, Germany) Dr Mike Dunne (IPP-Garching) Dr Patrick Blanchard (Swiss Plasma Center (SPC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne,Switzerland) Dr Samuli Saarelma (CCFE) Dr Stanislas Pamela (CCFE - UKAEA) Dr Stefano Coda (CRPP-EPFL) Dr Umar Sheikh (Swiss Plasma Center (SPC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne,Switzerland)