Impurity enrichment and radiative enhancement using induced SOL flow in DIII-D

Experiments on DIII-D have demonstrated the efficacy of using induced scrape-off-layer (SOL) flow to preferentially enrich impurities in the divertor plasma. This SOL flow is produced through simultaneous deuterium gas injection at the midplane and divertor exhaust. Using this SOL dow, an improvement in enrichment (defined as the ratio of impurity fraction in the divertor to that in the plasma core) has been observed for all impurities in trace-level experiments (i.e., impurity level is non-perturbative), with the degree of improvement increasing with impurity atomic number. In the case of argon, exhaust gas enrichment using modest SOL flow is as high as 17. Using this induced SOL flow technique and argon injection, radiative plasmas have been produced that combine high radiation losses (P-rad/P-input > 70%), low core fuel dilution (Z(eff) < 1.9), and good core confinement (tau(E) > 1.0 tau(E,ITER93H)) (C) 1999 Elsevier Science B.V. All rights reserved.