Characterization and conditioning of SSPX plasma facing surfaces

The Sustained Spheromak Physics Experiment (SSPX) will examine the confinem ent properties of spheromak plasmas sustained by DC helicity injection. Und erstanding the plasma-surface interactions is an important component of the experimental program since the spheromak plasma is in close contact with a stabilizing wall (flux conserver) and is maintained by a high current disc harge in the coaxial injector region. Peak electron temperatures in the ran ge of 400 eV are expected, so the copper plasma facing surfaces in SSPX hav e been coated with tungsten to minimize sputtering and plasma contamination , Here, we report on the characterization and conditioning of these surface s used for the initial studies of spheromak formation in SSPX. The high pre ssure plasma-sprayed tungsten facing the SSPX plasma was characterized in s itu using beta -backscattering and ex situ using laboratory measurements on similarly prepared samples. Measurements showed that water can be desorbed effectively through baking while the removal rates of volatile impurity ga ses during glow discharge and shot conditioning indicated a large source of carbon and oxygen in the porous coating. (C) 2001 Elsevier Science B.V. Al l rights reserved.