Open AccessDevelopment of NSTX Particle Control Techniques
Author(s) -
H. Kugel,
R. Maingi,
M.G. Bell,
D. Gates,
K. W. Hill,
B. LeBlanc,
D. Mueller,
R. Kaita,
S. Paul,
S.A. Sabbagh,
C.H. Skinner,
Vlad Soukhanovskii,
B. Stratton,
R. Raman
Publication year - 2004
Language(s) - English
Resource type - Reports
DOI - 10.2172/828583
Subject(s) - helium , materials science , plasma , glow discharge , atomic physics , nuclear engineering , cryopump , ohmic contact , impurity , chemistry , physics , nuclear physics , nanotechnology , organic chemistry , layer (electronics) , engineering
The National Spherical Torus Experiment (NSTX) High Harmonic Fast Wave (HHFW) current-drive discharges will require density control for acceptable efficiency. In NSTX, this involves primarily controlling impurity influxes and recycling. We have compared boronization on hot and cold surfaces, varying helium glow discharge conditioning (HeGDC) durations, helium discharge cleaning, brief daily boronization, and between discharge boronization to reduce and control spontaneous density rises. Access to Ohmic H-modes was enabled by boronization on hot surfaces, however, the duration of the effectiveness of hot and cold boronization was comparable. A 15 minute HeGDC between discharges was needed for reproducible L-H transitions. Helium discharge conditioning yielded slower density rises than 15 minutes of HeGDC. Brief daily boronization followed by a comparable duration of applied HeGDC restored and enhanced good conditions. Additional brief boronizations between discharges did not improve plasma performance (reduced recycling, reduced impurity luminosities, earlier L-H transitions, longer plasma current flattops, higher stored energies) if conditions were already good. Between discharge boronization required increases in the NSTX duty cycle due to the need for additional HeGDC to remove codeposited D