Wall conditioning on TEXTOR

Proper wall conditioning has been a major element in the development of fusion energy on the way to achieve high fusion plasma performance. Various of these techniques have been pioneered in the TEXTOR tokamak and later applied successfully in various devices worldwide. The main issues are to clean the surface from surface-bounded impurities, to remove hydrogen, and to coat the entire wall surface with a thin film of a proper first-wall material. The main benefits of wall conditioning are to control the oxygen impurity content of the plasma and to offer a suitable first-wall material. Entire coating of the first wall has allowed one to control to some extent the recycling hydrogenic fluxes but in particular to study the complex coupling between the choice of wall materials and the behavior of the plasma edge. This paper presents a review of the different wall-conditioning methods used in TEXTOR and their effects on the plasma behavior. Also, new wall-conditioning concepts, compatible with steady-state magnetic fields, are outlined briefly.