Speaker
Description
See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.102.pdf
A strong, favourable isotope dependence of the energy confinement (tao E,th ~ A^0.4) has been found in Hydrogen (H) and Deuterium (D) JET-ILW type I ELMy H-modes, originating at the pedestal [1]. Also, the plasma density is systematically lower in H than in D plasmas [1]. This contribution examines the isotopic dependence of the pedestal on linear MHD stability, ELM losses and pedestal structure in low delta type I ELMy H-modes in H and D. The direct isotope effect on pedestal stability is taken into account by including the diamagnetic frequency in the stability criterion with the ideal MHD HELENA/ELITE codes [2, 3, 4] and is found to be small. Interpretative EDGE2D-EIRENE simulations [5, 6] using the so-called 'corner-corner' divertor configuration and simultaneous upstream (ne, Te from Thomson-scattering (TS)) and outer divertor target profile (heat flux deposition from IR camera) constraints indicate higher separatrix temperature (Te,sep) and lower separatrix density in H than in D for a pair of discharges at similar stored energy (which required higher input power in H than in D). As Te,sep is used to position the profiles with respect to the separatrix, higher Te,sep in H translates into significant destabilisation of Peeling-Ballooning modes compared to D, which is consistent with type I ELMs being triggered at lower pedestal pressure in H. The ELM energy losses, evaluated from EFIT stored energies and TS kinetic profiles are found to be dominated by density loss both in H and D. At low ELM frequency (fELM), ELM particle losses (evaluated from interferometry) increase with fELM, in correlation with decreasing pedestal top density (ne,PED). Thus, the observed higher fELM in H than in D at same input power possibly contributes to the lower ne,PED in H. However, ELM particle losses saturate at higher fELM, both in H and in D, implying that other mechanisms may also play a role in the lower ne,PED in H. The pedestal density width is found to be narrower, or at most similar, in H than in D, in contradiction with the neutral penetration model (NPM) [7]. This challenges the validity of the NPM in the analysed pedestals and implying that fuelling inside the separatrix is not the only responsible physics mechanism for the difference between ne,PED in H and D. The EDGE2D-EIRENE simulations indicate that higher edge heat and particle transport in H than in D could be the main reason for the different pedestals.
[1] C.F. Maggi et al., PPCF 60, 014045 (2018)
[2] G.T.A. Huysmans et al., Comp. Phys. Proc. Int. Conf. 371 (1991)
[3] H.R. Wilson et al., PoP 9, 1277 (2002)
[4] P.B. Snyder et al., PoP 9, 2037 (2002)
[5] D. Reiter, JNM 196-198, 80 (1992)
[6] R. Simonini et al., CPP 34, 368 (1994)
[7] R.J. Groebner et al., PoP 9, 2134 (2002)
