Relationship between density peaking, particle thermodiffusion, Ohmic confinement, and microinstabilities in ASDEX Upgrade L-mode plasmas -: art. no. 040701

New experimental results obtained in ASDEX Upgrade [O. Gruber, H.-S. Bosch, S. Gunter et al., Nucl. Fusion 39, 1321 (1999)] plasmas in low confinement mode with central electron cyclotron heating are presented in which transitions in both the particle and electron heat transport properties have been observed. A comprehensive albeit qualitative explanation for both the transport channels is provided in the framework of the theory of ion temperature gradient and trapped electron mode microinstabilities. The different transport behaviors are related to the dominant instability at play and to the collisionality regime. In particular, central electron heating induces a flattening of the density profile when the dominant instability is a trapped electron mode, and density peaking is observed to increase with decreasing collisionality. (c) 2005 American Institute of Physics.