IN-SITU, REAL-TIME ELLIPSOMETRY OF EROSION IN PISCES-B MOD

A fixed angle, single wavelength laser ellipsometer was tested in PISC ES-B Mod as a real-time diagnostic for making in situ erosion rate mea surements. Film thickness measurements were made using a wavelength of 632.8 nm and an angle of incidence of 47.5 degrees at better than 1 n m resolution over a pathlength of several meters. Measurements were ma de through a deuterium plasma, which produced an ion flux to test samp les of about 2 x 10(17) D/cm(2)s. Erosion rates of < 1 nm/s were readi ly detected and the measured rate for 100 eV D+ at normal incidence on SiO2 was found to be about 0.04 nm/s, in reasonable agreement with th e calculated physical sputtering yield.