Speaker
Edoardo Alessi
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1044.pdf
Operational diagrams for MHD instabilities limiting plasma
performances in JET D-T Scenarios with ILW
E. Alessi1, P. Buratti2, E. Giovannozzi2, T. O'Gorman3, G. Pucella2, M.Baruzzo4, E.Joffrin5,
S.Nowak1, F.G. Rimini3 and JET Contributors*
EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK
1
IFP-CNR, via R. Cozzi 53, Milano, Italy
2
ENEA C. R. Frascati, via E. Fermi 45, Frascati (Roma), Italy
3
CCFE, Culham Science Centre, Abingdon, United Kingdom
4
Consorzio RFX, Corso Stati Uniti 4, Padova, Italy
5
CEA, IRFM, Saint Paul Lez Durance, France
(*) See the auhor list of X. Litaudon et al 2017 Nucl. Fusion 57 102001
One of the major aims of nowadays JET experimental campaigns is the execution of D-T
experiments with a metallic tokamak (ILW, ITER-like wall) wall [1-2]. At present,
experiments are devoted to develop scenarios capable of sustaining high performances for
>5s. Two scenarios are considered with this aim: the Baseline H-mode Scenario, and the
Hybrid Scenario.
High performances and duration can be limited by the onset of MHD modes or by the
influx of high Z impurities in the plasma core [3,4,5]. MHD modes can foster the
accumulation of impurities [4] and, on the other hand, an excess of impurities in the core
plasma degrades the current density profile providing the conditions to lower the thresholds
for triggering MHD instabilities. Then, to identify the conditions under which NTMs are
the main cause limiting the plasma performances, the statistical analysis of the MHD onset
conditions has been undertaken distinguishing between the trigger causes (e.g., Sawteeth)
and the presence or not of impurities in the plasma. The latter condition has been found
effective in indicating that cases of n=2 onsets (not Sawtooth triggered) at low ßN in the
Hybrid scenario are mainly due to plasma profiles already degraded by impurity influx.
The analysis here presented takes into account all pulses performed in Hybrid scenario
during the 2015-2016 JET campaign (~250 pulses), and a selected list of ~90 pulses for the
Baseline scenario.
References:
[1] X. Litaudon et al 2017 Nucl. Fusion 57 102001
[2] L. Horton et al 2016 Fusion Eng. Des. 109–11 925
[3] P. Buratti et al 2015 42nd EPS Conf. on Plasma Physics (Lisbon) P2.115
[4] T. Hender et al. 2016 Nucl. Fusion 56 066002
[5] I Nunes and the JET Contributors 2016 Plasma Phys. Control. Fusion 58 014034
