ISX: a tokamak for surface and impurities studies

The ISX (Impurity Study Experiment) is a moderate size tokamak slightly larger than the ORMAK tokamak. ISX is being built explicitly for the study of impurities and plasma-wall interactions. It is scheduled to begin experiments in the spring of 1977. Several features have been deliberately designed into the ISX which make it particularly adaptable to surface studies. The first is a welded stainless steel vacuum system, bakeable to 4000C, with a projected base pressure greater than or equal to 2 x 10-9 torr. Another feature is that of ''easy'' demountability of the vacuum system. Replacement of the entire vacuum system should take about two weeks. A third feature is diagnostic access to the edges of the plasma. The initial surface physics question to be answered is how best to keep surfaces clean: by baking, by direct or indirect wall bombardment discharges, or by gettering. Later experiments will involve using wall materials other than stainless steel to determine their effects on the plasma