Plasma-surface interaction studies in the HL-1 tokamak

The plasma-surface interaction (PSI) studies in HL-1 were carried out under the condition of an all metal wall, typically at an ohmic heating plasma current of 100 kA, a pulse duration of 0.6 s and a toroidal magnetic field of 2 T. Two mass spectrometers, a Langmuir probe and surface probes were developed to study particle flux arriving at and leaving the surface. From the time evolution of the pumped rate for the major gaseous impurities of H2O, CH4 and CO after an ohmic heating discharge, it is shown that the formations of H2O, CH4 and CO are due to, respectively, different types of surface chemical reactions. (orig.)