(EX/P3-16) Overview of Poloidal and Toroidal Momentum Transport Studies in JET

T. Tala1), Y. Andrew2), K. Crombé3), P.C. de Vries2), X. Garbet4), N. Hawkes2), H. Nordman5), K. Rantamäki1), P. Strand5), A. Thyagaraja2), J. Weiland5), E. Asp5), Y. Baranov2), C. Challis2), G. Corrigan2), A. Eriksson5), C. Giroud2), M.-D. Hua2), I. Jenkins2), H.C.M. Knoops6), X. Litaudon4), P. Mantica7), V. Naulin8), V. Parail2), K.-D. Zastrow2), JET-EFDA Contributors*
1) Association EURATOM-Tekes, VTT, P.O. Box 1000, FIN-02044 VTT, Finland
2) EURATOM/UKAEA Fusion Association, Culham Science Centre, Oxon. OX14 3DB, UK
3) Department of Applied Physics, Ghent University, Belgium
4) Association EURATOM-CEA, CEA/DSM/DRFC Cadarache, St Paul-Lez-Durance, France
5) Association EURATOM-VR, Chalmers University of Technology, Göteborg, Sweden
6) Eindhoven University of Technology, Dept. of Applied Physics, The Netherlands
7) Istituto di Fisica del Plasma CNR-EURATOM, via Cozzi 53, 20125 Milano, Italy
8) Association Euratom-Riso National Laboratory, DK-4000 Roskilde, Denmark
*See Appendix of M.L. Watkins et al., Fusion Energy 2006 (Proc. 21st Int. Conf. Chnegdu 2006), IAEA Vienna (2006)

Abstract.  It is well known that the ExB shear flow is one of the major players in quenching turbulence. As E×B shear flow is closely related to poloidal and toroidal rotation, understanding of momentum transport is one of the key elements to achieve high fusion performance, good confinement and access to regimes with transport barriers. This paper reports on the recent studies of poloidal and toroidal momentum transport in JET. The experimental results show that the carbon poloidal rotation of an order of magnitude above the neo-classical estimate within the ITB. The main candidate to explain the large measured poloidal rotation is thought to be the turbulence driven poloidal velocity through the Reynolds stress. Simulation results with both TRB and CUTIE turbulence codes indicate that the turbulent driven poloidal velocity can well be of the order a few 10 km/s and thus, could explain the difference between meas-ured and neo-classical values. Concerning the toroidal momentum transport, the analysis of high density ELMy H-mode discharges with ITG dominated turbulence shows that the ratio of the effective momentum and ion heat diffusivity is in the range 0.1-0.4. This ratio seems to be lower on JET than on other tokamaks, and lower than the commonly assumed ratio of 1. While the ion temperature profiles are stiff, the rotation profiles are not, as increasing torque does not increase the momentum diffusion coefficient. A deeper theoretical understanding of this is in progress. The torque profiles in these high density plasmas are hollow while rotation profiles are peaked. Thus, an inward momentum pinch might be needed, and this is also predicted by the new version of the Weiland model with self-consistent calculation of toroidal rotation. The existence of the pinch combined with low momentum diffusion coefficient gives rise to the possibility to have non-flat and possibly larger than expected toroidal rotation profiles in ITER.

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