Surface impurities studies during the start-up and early operations of ISX-A using a surface analysis station with sample transfer

A surface analysis station was installed on ISX-A before start-up which provided data on samples of wall material and a variety of other materials exposed at positions between the first wall and the limiter inner radius. Samples were introduced, from air, into an ultra-high vacuum transport system without disturbing the vacuum in ISX-A or the analysis station. An Auger electron spectrometer in the analysis station along with other diagnostics provided information on the initial “clean up” as well as the subsequent routine operation of ISX-A. During the start-up period substantial sulfur contamination was evident but this was greatly reduced as hydrogen discharge cleaning proceeded. Samples of oxidized stainless steel were not cleaned to an oxygen-free status but the surface was reduced to a thin substoichiometric oxide. Carbon was significantly removed but not eliminated entirely. Routine tokamak operations were monitored by a means of a special composite sample which made possible estimates of both the state of cleanliness of the system and its rate of clean-up.