Physics of transport in tokamaks
This paper is an overview of recent results related to turbulent particle and heat transport, and triggering of Internal Transport Barriers. Particle transport is characterised by a pinch velocity that is found to be larger than the value predicted by theory of collisional transport (Ware pinch) in L-mode plasmas. Also it increases with magnetic shear. In H-mode, density peaking decreases with collisionality. Pinch velocity reaches the Ware value for large collision frequencies. Heat transport has made progress along two directions: dimensionless scaling laws and analysis of modulation experiments. Dimensionless scaling law of thermal confinement agrees with the prediction for electrostatic turbulence. Dependence with collisionality remains to be understood. Heat modulation experiments have been investigated in several devices using a critical gradient model, micro-stability analysis and predictive modelling. Thresholds and stiffness are correctly reproduced by stability analysis and modelling with Weiland model. Analysis with a critical gradient model leads to a large variability of stiffness. Finally the question of triggering Internal Transport Barriers has been addressed by analysing electron transport barriers. It is confirmed that negative magnetic shear combined with Shafranov shift is a robust stabilising mechanism. However, some well established features of internal barriers are hardly explained by theory, in particular the role of low order rational values of the minimum safety factor, and the existence of multiple barriers.
Bibliographic Reference: An oral paper given at: 31st EPS Conference on Controlled Fusion and Plasma Physics Organised by: CCLRC Rutherford Appleton Laboratory (GB); EURATOM/UKAEA Fusion Association (GB) Held at: Imperial College London(GB)
Availability: Available from Association EURATOM-CEA, Departement de Recherches sur la Fusion Controlee, CEA Cadarache, F-13108 St Paul-Lez-Durance, France Tel: (+33) 4 42 25 70 01; Fax: (+33) 4 42 25 64 21 E-mail: firstname.lastname@example.org
Record Number: 200417719 / Last updated on: 2004-10-14
Original language: en
Available languages: en