PLASMA SPUTTERED MO IMPURITY TRANSPORT EXPERIMENT IN PISCES-B MOD - ASSESSMENT OF ATOMIC PROCESS RATE COEFFICIENTS AND REDEPOSITION CHARACTERISTICS

In this experiment, a molybdenum marker embedded at the center of a gr aphite substrate is used to study the transport of Mo over the surface under redeposition conditions. The sputtered Mo atoms undergo a numbe r of events (excitation, ionization, de-excitation) in front of the sa mple before being redeposited. These events can be linked to observabl e quantities measured by plasma diagnostics. Plasma density and electr on temperature are measured by Langmuir probes. Optical emission spect roscopy is used to obtain neutral and ionized Mo and Ar emission profi les in the plasma column. New techniques are introduced to evaluate bo th excitation and ionization rate coefficients from the measured Mo I line intensity profiles. The measured coefficients are compared to the oretical calculations and a good agreement is found. After plasma expo sure, 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 c ode.