BORONIZATION OF THE TJ-I TOKAMAK BY TRIMETHYLBORON AND DECABORANE

The small TJ-I Tokamak (R = 0.3 m, a = 0.095 m) has been boronized by GD of trimethylboron (TMB) and decaborane in their admixtures with H-2 and He at room temperature. A strong reduction in metal, C and O flux es, followed by a significant reduction in the total radiated power an d a moderate decrease in plasma resistivity was observed, together wit h a broadening in the radial profile of plasma emissivity. The results , that represent the first successful operation of a small (a < 10 cm) tokamak under boronized conditions to our knowledge, are analyzed in terms of impurity production mechanisms and they are compared to those from bigger machines under similar wall conditions and to other plasm as of similar size under oxygen-free conditions. A similar beneficial effect with respect to plasma contamination in the TJ-I compared to bi gger devices is deduced, if allowance for the presence of partially io nized light impurities in the plasma center is made.