Particle flow during sawtooth reconnection. Numerical simulations of experimental observations

The core plasma density in ohmic, sawtoothing regime in Tore Supra and JET tokamaks measured by fast-sweeping reflectometry develops a central peak. This peak is surrounded by a density plateau, which extends up to the q = 1 reconnection surface. Such mexican hat like profiles differ from the smooth dome of the temperature profile. Detailed tomographic reconstructions of the density in the poloidal plane show the development of crescent and ring structures during the sawtooth cycle. 3D full MHD nonlinear simulations with the XTOR-2F code recover these structures and show that they can be explained by the MHD activity related to the sawtooth instability. They show also that the electron density evolution is dominated by the perpendicular MHD flows, while the temperature, obtained with ECE measurements is dominated by parallel diffusion. (author)