Glow discharge cleaning of carbon fiber composite and stainless steel A. Airapetov a , L. Begrambekov a,⇑,1 , S. Brémond b , D. Douai b , A. Kuzmin a , Ya. Sadovsky a , P. Shigin a , S. Vergasov a a Moscow Engineering and Physics Institute, 31 Kashirskoe shosse, Moscow 115409, Russian Federation b CEA/IRFM, Association EURATOM-CEA, Centre de Cadarache, 13108 Saint Paul Lez Durance, France article info Article history: Available online 2 November 2010 abstract The paper experimentally investigates and analyses the features and mechanisms of both of oxygen removal by deuterium glow discharge from CFC, pyrolytic graphite and stainless steel subjected to irra- diation in oxygen contaminated plasma. It is shown that oxygen implanted in pyrolytic graphite (PG) per- pendicular to basal plates is removed after sputtering the layer slightly thicker than oxygen stopping zone (2 nm). Fast deuterium ions penetrating into CFC during GDC transfer the trapped oxygen atoms into the bulk. Thus, much thicker surface layer has to be removed (500–1000 nm) for oxygen release. Irradiation of stainless steel in plasma leads to formation of a barrier layer with thickness (2–4 nm) equal, or slightly higher than stopping range of oxygen ions. The layer accumulates the main fraction of implanted oxygen and prevents its penetration into the bulk. After barrier layer sputtering oxygen spreads into the bulk. Parameters and conditions of optimum GDC are discussed. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Oxygen impurity presenting in plasmas of fusion devices leads to a number of negative effects. Among them there are parasitic radiative power, dilution of fuel particles, accelerated erosion rate of plasma facing materials, enhanced trapping and recycling of fuel particles. Various types of discharges providing irradiation of plasma fac- ing materials with weakly ionized plasma (glow discharge, rf-dis- charge, Taylor discharge) are routinely used for removal of oxygen and other impurities from the first walls of today tokam- aks. Nevertheless the mechanisms of oxygen release from the ion irradiated metal and graphite are not understood satisfactory. Its detailed investigation seems to allow optimization of the condi- tioning process. The paper is devoted to the results of experimental investiga- tion of oxygen (O) removal by a deuterium (D) glow discharge (D 2 -GDC) from carbon fiber composite (CFC), pyrolytic graphite (PG) and stainless steel (SS). Parameters, peculiarities and mecha- nisms of O release by D 2 -GDC from CFC, PG and SS irradiated in O contaminated plasmas are presented. The experiments were performed in the electron initiated dis- charges. Parameters of irradiating ion flux were rather close to those of a glow discharge. Thus, we use the term GDC for surface cleaning process realized in this study. 2. Experimental The experiments with CFC samples were performed in the ther- mal desorption device – (TDS-1) presented earlier [1]. The main feature of the TDS-1 is the possibility to irradiate the samples in the gas discharge ignited in the plasma chamber of the stand, and to make a thermal desorptional analysis of the samples in the same plasma chamber. The experiments with SS samples were performed in the ther- mal desorption stand (TDS-2). The main parts of TDS-2 (Fig. 1) are lock chamber (1), ion gun chamber (2), plasma chamber (3), TDS chamber (4), and sample manipulator (5). All vessels are pumped down by turbo molecular pumps through pipe branches (6). The third and fourth vessels are annealed before- and water- cooled during experiments (7). The sample manipulator carries the sample (8), sample heater (9) and thermocouple (not shown in Fig. 1). It passes through the pipe branches (10), gate valves (11), feed through (12), sealing (13). Chamber (2) is intended for sample irradiation with ion beam and is not used in the experiments. Chamber (3) allows sample irradiation in a gas discharge plasma. It contains the electrode sys- tem (14) and (15) for maintaining the gas discharge, Langmuir probe (16) and screen (17). The thermal desorptional investigations are performed in vessel (4) with help of the quadruple mass-spectrometer QMS-200 (19). The vessels are fed with working gas through gas inlets (20). 0022-3115/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2010.10.054 ⇑ Corresponding author. Address: NRNU MEPhI, 31 Kashirskoe shosse, Moscow 115409, Russian Federation. E-mail address: lbb@plasma.mephi.ru (L. Begrambekov). 1 Presenting author. Journal of Nuclear Materials 415 (2011) S1042–S1045 Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat