(OV/4-2) Overview of TJ-II experiments

J. Sanchez1), M. Acedo1), A. Alonso1), J. Alonso1), P. Alvarez1), F. de Aragón1), E. Ascasíbar1), A. Baciero1), R. Balbín1), L. Barrera1), E. Blanco1), J. Botija1), B. Brañas1), E. de la Cal1), E. Calderón1), I. Calvo1), A. Cappa1), J. M. Carmona1), R. Carrasco1), B. A. Carreras2), F. Castejón1), G. Catalán1), M. Chamorro1), A. A. Chmyga3), N. B Dreval3), S. Eguilior1), L. Eliseev4), J. Encabo1), T. Estrada1), A. Fernández1), R. Fernández1), J. A. Ferreira1), J. M. Fontdecaba1), C. Fuentes1), J. de la Gama1), A. García1), L. García6), I. García-Cortés1), J. M. García-Regaña1), B. Gonçalves7), J. Guasp1), J. Herranz1), A. Hidalgo1), C. Hidalgo1), J. A. Jiménez1), D. Jiménez1), R. Jiménez-Gómez1), I. Kirpitchev1), A. D. Komarov3), A. S. Kozachok3), L. Krupnik3), F. Lapayese1), M. Liniers1), D. López-Bruna1), A. López-Fraguas1), J. López-Rázola1), A. López-Sánchez1), E. de la Luna1), G. Marcon1), F. Martín1), L. Martínez-Fresno1), K. J. McCarthy1), F. Medina1), M. Medrano1), A. V. Melnikov4), P. Méndez1), B. van Milligen1), E. Mirones1), I. S. Nedzelskiy7), M. Ochando1), J. Olivares1), R. Orozco1), P. Ortiz1), J. L. de Pablos1), L. Pacios1), I. Pastor1), M. A. Pedrosa1), A. de la Peña1), A. Pereira1), D. Pérez-Risco1), A. Petrov5), S. Petrov8), A. Portas1), D. Rapisarda1), L. Ríos1), C. Rodríguez1), L. Rodríguez-Rodrigo1), E. Rodríguez-Solano1), J. Romero1), A. Ros1), A. Salas1), E. Sánchez1), M. Sánchez1), E. Sánchez-Sarabia1), X. Sarasola1), K. Sarksian5), S. Schchepetov5), C. Silva7), N. Skvortsova5), A. Soleto1), F. Tabarés1), D. Tafalla1), J. Tera1), A. Tolkachev1), V. Tribaldos1), I. Vargas1), J. Vega1), G. Velasco1), M. Weber1), G. Wolfers1), B. Zurro1)
1) CIEMAT, Madrid, Spain
2) Oak Ridge National Laboratory Oak Ridge TN 37831 USA
3) Institute of Plasma Physics, NSC KIPT, 310108 Kharkov, Ukraine
4) Institute of Nuclear Fusion, RNC Kurchatov Institute, Moscow, Russia
5) General Physics Institute, Russian Academy of Sciences, Moscow, Russia
6) Carlos III University, Madrid, Spain
7) Associação EURATOM/IST, Centro de Fusão Nuclear, 1049-001 Lisboa, Portugal
8) A.F. Ioffe Physical Technical Institute, 194021 St. Petersburg, Russia

Abstract.  This paper presents an overview of the experimental progress made in TJ-II. Confinement and electric fields: Energy confinement time follows the ISS04 scaling. Local electron heat diffusion decreases in regions close to low order rationals and increase with heating power. A direct link between electric fields, density and plasma confinement has been found. Positive radial electric fields are measured in ECRH plasmas; and negative plasma potentials with NBI. Transitions and magnetic topology: The threshold density needed to trigger e-ITBs depends on the order of the rational magnetic surface. Quasi-coherent modes, found close to the radial location of the internal barrier foot vanish once the internal barrier is fully developed. Electrode biasing experiments show that it is possible to modify the edge radial electric field and the particle confinement for both polarities Plasma rotation and momentum re-distribution: Impurity poloidal rotation measurements show a link between plasma density and rotation. The generation of spontaneous perpendicular edge sheared flows requires a minimum plasma density. It has been recently 2-D visualized by means of fast cameras. As sheared flows develop turbulence structures become stretched indicating a modification in the perpendicular degree of turbulence anisotropy. Experimental results show significant turbulent parallel forces at plasma density rises above the threshold value. Shear flow physics involves 3-D phenomena in which both perpendicular and parallel dynamics play a role. MHD and plasma stability: Although magnetic well is the main stabilizing mechanism, plasma profiles are not dramatically affected when magnetic well is removed in the plasma edge. This result, consistent with recent findings in LHD, calls into question stability calculations (Mercier, Ballooning) based on assuming smooth pressure profiles. Analysis of ELM like events based on the coupling of ion-temperature-gradient modes to Alfvén and acoustic modes will be reported. The impact of magnetic topology (ripple) on the appearance of ELMs is under investigation. Plasma-wall studies: Configurations having rational numbers resulting in island chains at the edge have been explored for possible application in ``divertor-type” plasmas. Experiments aimed at characterizing the fuelling efficiency of plasma particles and injected impurities will be reported.

Full paper and slides available (PDF)