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(CDP/03) Core and Edge Electron Dynamics during Lower Hybrid Current Drive Experiments

   
Y. Peysson , M. Goniche , R. Arslanbekov , A. Bécoulet , P. Bibet , A. Côté ¹, C. Côté ¹, Y. Demers ¹, P. Froissard , V. Fuchs ¹, Ph. Ghendrih , A. Grosman , J. Gunn ², D. Guilhem , J. H. Harris ³, J. Hogan ⁴, F. Imbeaux , P. Jacquet ¹, F. Kazarian , X. Litaudon , J. Mailloux , D. Moreau , V. Petrzìlka ⁵, R. Pugno ⁶, K. M. Rantamäki ⁷, G. Rey , N. Richard ¹, E. Sébelin , M. Shoucri ¹
 
Association EURATOM-CEA CEA/Cadarache, 13108 Saint Paul-lez-Durance Cédex France
¹ Centre Canadien de Fusion Magnétique, Varennes, Québec, J3X 1S1, Canada
² MPB Technologies inc. Pointe-Claire, Québec, Canada
³ Australian National University, Canberra, ACT0200, Australia
⁴ Oak Ridge National laboratory, Oak Ridge, Tenessee, USA
⁵ Institut of Plasma Physics, 182 21 Praha 8, Czech Republic
⁶ Consorzio RFX, IGI Padova, 4 Corsi Stati Uniti, Padova, Italy
⁷ Association EURATOM-TEKES, Espoo, Finland

Abstract
Characterisation of the core and edge fast electron dynamics during lower hybrid (LH) current drive experiments is a critical issue in view to achieve improved plasma performances by tailoring the current density profile  in a steady state manner. At low power input ( $\rm P_{LH} \le 2MW$), the localisation of the LH wave absorption exhibits a correlation with the radial position of the $q = 1$ surface in the plasma, as deduced from magnetic measurements and equilibrium code predictions. Such an effect is observed either in stationary or transient conditions during LH assisted ramp-up experiments . The lack of LH power deposition in the core of the plasma is also confirmed by analysis of giant sawteeth  in combined ICRH-LH scenarios. The implications of these results for theories of the LH wave dynamics in the plasma and current density profile control are discussed. LH power dissipation at the plasma edge, which may lead to anomalous heat loads on components magnetically connected to the radiating waveguide array is investigated theoretically and experimental data are compared to calculations. The key role played by the fraction of high-n$_{//}$ values of the LH wave power spectrum as well as the edge plasma density in the acceleration of thermal electrons is identified, and the possibility of an additional driving force is also discussed. The effect of the shape of the LH waveguide septa is analysed both theoretically and experimentally.

lower hybrid current drive 

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