Author/Authors :
M. Richou، نويسنده , , C. Martin، نويسنده , , P. Delhaès، نويسنده , , M. Couzi، نويسنده , , W. Saikaly، نويسنده , , C. Brosset، نويسنده , , B. Pégourié، نويسنده , , A. Litnovsky، نويسنده , , V. Philipps، نويسنده , , P. Wienhold، نويسنده , , J. Dentzer، نويسنده , , C. Vix-Guterl، نويسنده , , P. Roubin، نويسنده ,
Abstract :
For safety reasons, the formation of carbon deposits in tokamaks must be limited. To understand how these deposits are formed, a comparative study of the characteristics of carbon deposits collected in TEXTOR and Tore Supra tokamaks has been performed. Both deposits exhibit self-similar morphologies like asparagus tips. Transmission electron microscopy performed on thin foils also reveals structure and texture similarities, with the existence of a regular network of parallel mesopores. Besides, methane adsorption isotherm measurements give evidence for microporosity (0.01 cm3 g−1 for TEXTOR and 0.06 cm3 g−1 for Tore Supra). Raman microspectrometry as well as temperature programmed desorption experiments demonstrate the presence of polyaromatic species, at the origin of the disordered graphitic nature of these carbons. The analysis of samples heat-treated at 2500 °C indicates that they graphitize only to a limited extent due to the existence of nanoparticles. Metallic and ferromagnetic inclusions are also evident inside the deposits. These results therefore suggest complex growth processes, mixing homogeneous nucleation and vapor deposition, similar to what can be observed for catalytic chemical vapor deposition processes.
