Optimization of pellet scenarios for long pulse fuelling to high densities at JET

• Published in: Nuclear fusion 2002-04, Vol.42 (4), p.388-402
• Main Authors: Lang, P.T, Alper, B, Baylor, L.R, Beurskens, M, Cordey, J.G, Dux, R, Felton, R, Garzotti, L, Haas, G, Horton, L.D, Jachmich, S, Jones, T.T.C, Lomas, P.J, Lorenz, A, Maraschek, M, Müller, H.W, Ongena, J, Rapp, J, Reich, M, Renk, K.F, Sartori, R, Schmidt, G, Stamp, M, Suttrop, W, Villedieu, E, Collaborators, EFDA-JET Work Programme
• Format: Article
• Language: English
• Subjects: Applied sciences; Computer simulation; Controled nuclear fusion plants; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fuel injection; Fueling, heating and ignition; Installations for energy generation and conversion: thermal and electrical energy; Optimization; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma production and heating; Plasmas; Tokamak devices
• ISSN: 0029-5515; 1741-4326
• DOI: 10.1088/0029-5515/42/4/303

Pellet injection was investigated for its fuelling capability to high densities in ELMy H mode discharges at JET. Applying the high field side launch system, optimized refuelling scenarios were developed on the basis of conventional discharge configurations with I p = 2.5 MA, B t = 2.4 T, averaged triangularity ⟨δ⟩≈0.34 and mainly neutral beam heating at a level of approximately 17 MW. The accessible operational range was extended with respect to gas puff refuelling by the use of pellet injection. For example, H mode conditions could be maintained at densities beyond the Greenwald level. Plasma energy confinement was observed to become density independent at high densities. Deep pellet particle deposition made possible the uncoupling of edge and core density, allowing more peaked density profiles. When confinement deterioration due to pellet triggered MHD activity or parasitic pellet borne gas was avoided in appropriate pulse schedules, an enhanced particle inventory was achieved while maintaining the plasma pressure profile. In a technical assessment it was found that there is still room for further enhancement of the injection scenario by improved adaptation to high density plasma operation.