CNR ExploRA

Contributo in atti di convegno, 2021, ENG

Termination of discharges in high performance scenarios in JET

Sozzi C.; Alessi E.; Lomas P.J.; Rimini F.; Stuart C.; Challis C.; Garzotti L.; Lemmholm M.; Gerasinov S.; Maggi C.; Valcarcel D.; Hobirk J.; Kappatou A.; Pau A.; Sauter O.; Fontana M.; Marceca G.; Ferreira D.R.; Carvalho I.S.; Aleiferis A.; Cannas B.; Fanni A.; Sias G.; De La Luna E.; Frigione D.; Pucella G.; Giovannozzi E.; Joffrin E.; Lerche E.; Van Eester D.; Piron L.; JET Contributors

Istituto per la Scienza e Tecnologia dei Plasmi-Consiglio Nazionale delle Ricerche, Milano, Italia; United Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, Culham Science Centre Abingdon, United Kingdom; Max Planck Institute for Plasma Physics Garching, Germany; Swiss Plasma Centre - École Polytechnique Federale de Lausanne, Switzerland; Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal; Institute for Nuclear and Radiological Science and Technology, Safety and Energy, Athens, Greece; Electrical and Electronic Engineering Department, University of Cagliari, Italy. Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain; ENEA, Fusion and Nuclear Safety Department, C.R. Frascati, Roma, Italy; CEA, IRFM, St Paul Les Durance, France; Laboratory for Plasma Physics, École Royale Militaire, Brussel, Belgium; Dipartimento di Fisica "G. Galilei", Universita' degli Studi di Padova and Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA), Padova, Italy.

The termination of high performance plasmas in tokamak devices with high Z metal plasma facing components presents challenges related to the influx of heavy impurities which, if not kept under control, cause an increase of the radiative losses, radiative cooling and high probability of disruption. A number of key players in these dynamics have been identified by intensive research performed after the first years of operation in achines as AUG and JET in preparation of ITER operation. Inward neoclassical convection related to the peaking of the density profile, poloidal asymmetries, plasma rotation and centrifugal effects, temperature screening, pedestal temperature, pedestal density and ELMs control are among them. The objective of D-T fuelled plasmas with high neutron yield in stationary conditions, foreseen in the near future at JET, focuses the perations towards high performance in terms of thermal energy content and plasma current and consequently with higher disruption risk. The reduction of such risks is being pursued for the specific features of the two plasma scenarios being developed, baseline (?N ~1.8, q95 ~ 3) and hybrid (?N ~2-3, q95~4). The analysis of the previous experimental campaign and the data so far collected in the present campaign indicate that the combination of edge and core W control is needed to obtain a safe plasma termination, with the optimized use of the available actuators: gas and pellet for ELMs control, ramp-down waveform of the NBI heating power while maintaining a relevant ICRH additional power, sweeping of the separatrix hitting point on the divertor to reduce the heat load and to decrease the W source.

28th IAEA Fusion Energy Conference (FEC 2020), pp. 1–8, Virtual Event, 10-15 maggio 2021