Overview of impurity control and wall conditioning in NSTX

The national spherical torus experiment (NSTX) started plasma operations in February 1999. In the first extended period of experiments, NSTX achieved high current, inner wall limited, double null, and single null plasma disch arges, initial Coaxial Helicity Injection, and high harmonic fast wave resu lts. As expected, discharge reproducibility and performance were strongly a ffected by wall conditions. In this paper, we describe the internal geometr y, and initial plasma discharge, impurity control, wail conditioning, erosi on, and deposition results. (C) 2001 Elsevier Science B.V. All rights reser ved.