Plasma sputtered Mo impurity transport experiment in PISCES-B Mod; assessment of atomic process rate coefficients and redeposition characteristics

Abstract

In this experiment, a molybdenum marker embedded at the center of a graphite substrate is used to study the transport of Mo over the surface under redeposition conditions. The sputtered Mo atoms undergo a number of events (excitation, ionization, de-excitation) in front of the sample before being redeposited. These events can be linked to observable quantities measured by plasma diagnostics. Plasma density and electron temperature are measured by Langmuir probes. Optical emission spectroscopy is used to obtain neutral and ionized Mo and Ar emission profiles in the plasma column. New techniques are introduced to evaluate both excitation and ionization rate coefficients from the measured Mo I line intensity profiles. The measured coefficients are compared to theoretical calculations and a good agreement is found. After plasma exposure, energy dispersive X-ray analysis (EDX) is used to measure the Mo impurity concentration on the graphite surface. These concentrations are then compared to simulated redeposition flux obtained by the WBC code.