Plasma growth processes inside gaps of the castellated limiter of the Tore Supra tokamak

¹ Aix-Marseille Univ, PIIM; CNRS, UMR 6633, 13397 Marseille Cedex 20, France
² Association Euratom-CEA sur la Fusion Contrôlée, Cadarache, 13108 Saint-Paul-Lez-Durance Cedex, France

^a e-mail: rufferemy@aol.com

Received: 15 April 2011
Revised: 21 July 2011
Accepted: 12 September 2011
Published online: 28 October 2011

Abstract

We performed electron microscopy analysis of carbon tiles dismantled from the toroidal limiter of the Tore Supra tokamak. The tile top surfaces are either eroded, or covered with deposits, depending on ion flux. On the contrary, the tile gap surfaces are covered with deposits whatever the region of the limiter. We analyzed both the topography and the microstructure of gap deposits. Deposits are tip-shaped and deposition is significant only down to ~1 mm, due to the limited penetration of ions. The direction of tips results from the combination of the ion speed along the magnetic lines and the drift associated to the local electric fields. The microstructure of deposits reveals the presence of graphitic species, such as onion-like nanoparticles, and our results therefore show that deposition results from local plasma chemistry similar to what is observed for cold plasmas.