STUDY OF THE PLASMA MATERIAL INTERACTION DURING SIMULATED PLASMA DISRUPTIONS

During disruptions the plasma facing material of a next-generation tokamak will be exposed to very high heat loads under which the material will show severe erosion. Present estimates which are based on simulation experiments by electron beam or laser predict a very limited disruption lifetime of the component due to excessive thermal erosion. In contrast to the laboratory experiments on which these estimates are based, during a tokamak disruption the eroded material enters the incident plasma and interacts with it. Due to this interaction the actual disruption erosion occurring in a tokamak may be considerably different. The aim of the present work is to investigate the interaction of thermally eroded carbon material with a dense hydrogen plasma by means of quantitative emission spectroscopy. Pyrolytic carbon specimens were subjected to plasma discharge pulses with a peak energy deposition of 375 J/cm2. The line emission of the eroded carbon species was observed and analyzed. The density of C+ ions was found to be strongly peaked in the plasma directly in front of the specimen surface whereas the density of C2+ ions increased monotonously over 10-15 mm in front of the specimen. The results indicate that strong radiation is emitted by the eroded material and that a large part of the eroded carbon neutrals is ionized within 10-mu-s duration.