IMPURITY TRANSPORT UNDER STEADY-STATE MAGNETIZED PLASMA BOMBARDMENT IN PISCES-B MOD

Erosion and redeposition of materials is a critical issue in determining the lifetime of plasma-facing components as well as the plasma cleanliness in fusion reactors. In this work, both experimental and modeling efforts have been made to understand the fundamental aspects of the materials erosion and redeposition behavior under plasma bombardment, using the PISCES-B Mod facility, the WBC impurity transport code, and the VFTRIM and ITMC surface codes. A small impurity source made of molybdenum or boron embedded in a host surface of graphite is exposed to a steady-state, magnetically confined argon plasma. The plasma density is about 2x10(12) cm(-3), and the electron temperature is about 18 eV. The ion bombarding energy to the surface is set at 100 and 150 eV. The magnetic field is about 500 G. Under these experimental conditions, about 70% of the sputtered impurity atoms are calculated to be redeposited on the graphite surface, resulting in a distribution of impurity atom concentration on the graphite surface. The measured impurity redeposition profile indicates a decay across the magnetic field, and reaches a steady-state profile after a certain plasma exposure time. A good agreement has been found between the experimental data and the results of modeling.