RT Journal Article
T1 Enhanced confinement induced by pellet injection in the stellarator TJ-II
A1 Garcia Cortes, Maria Isabel
A1 Mccarthy, K. J.
A1 Estrada, T.
A1 Tribaldos Macía, Víctor
A1 Medina-Roque, D.
A1 Van Milligen, B.
A1 Ascasibar, E.
A1 Carrasco, R.
A1 Chmyga, A. A.
A1 Garcia, R.
A1 Hernandez Sanchez, J.
A1 Hidalgo, C.
A1 Kozachek, A. S.
A1 Medina, F.
A1 Ochando, M.A.
A1 De Pablos, J.L.
A1 Panadero, N.
A1 Pastor, I.
AB Enhanced confinement is observed in neutral beam injector (NBI)-heated hydrogen discharges made in the stellarator TJ-II after the injection of a single cryogenic fuel pellet into the plasma core. In addition to the expected increase in electron density, ne, in the core after pellet injection (PI), the plasma diamagnetic energy content is seen to rise, with respect to similar discharges without PI, by up to 40%.Furthermore, the energy confinement time, sE diag, as determined using a diamagnetic loop, is enhanced when compared to predictions obtained using the International Stellarator Scaling law [H. Yamada et al., Nucl. Fusion 45, 1684 (2005)] and the triple product, ne _ Ti _ sE diag, exhibits a clear bifurcation point toward an improved confinement branch as compared to the branch product predicted by this scaling law. In general, once such a pellet-induced enhanced confinement (PiEC) phase has been established, it is characterized by steepened radial density gradients, by more negative plasma potential in the core, more negative radial electric fields, Er, across a broad plasma region, as well as by reductions in density and plasma potential fluctuations in the density gradient region. In addition, experimental observations show increased peaking of core radiation losses, this pointing to edge/core plasma decoupling. In parallel, neoclassical simulations of reference and PiEC plasmas predict increased particle and energy confinement times during a PiEC phase together with a more negative Er profile. Qualitative rather than quantitative agreement with experimental parameters is found, indicating that turbulence seems to play a significant role here. In summary, single cryogenic pellet injection facilitates the achievement of an enhanced operational regime that was previously not observed in NBIheated discharges of the TJ-II.
SN 1070-664X
YR 2023
FD 2023-07-01
LK https://hdl.handle.net/10016/39935
UL https://hdl.handle.net/10016/39935
LA eng
NO This work is financed by grants PID2020-116599RB-I00 and PID2021-125607NB-I00, funded by MCIN/AEI/10.13039/501100011033. This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No.101052200 - EUROfusion). Views and opinions expressed are those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. The authors acknowledge the contributions to HIBP data collection, analysis, and interpretation made by A. Melnikov, M. Drabinskiy, L. G. Eliseev, and P. Khabanov as part of the long-term trilateral collaboration between National Research Center ‘Kurchatov Institute,’ Moscow, Russia, led by S. Melnikov, the HIBP group from Kharkov Institute of Physics and Technology, Kharkov, Ukraine, leaded by L.I. Krupnik, and CIEMAT. We also acknowledge the TJ-II Team.
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RD 1 sept. 2024