Modification of the internal electric field by biasing of the divertor plates in the Tokamak de Varennes (TdeV)

The radial electric field inside the separatrix has been deduced from spectroscopic measurements of impurities on Tde V (Tokamak de Varennes), using the reduced radial momentum balance and two neoclassical models [R. D. Hazeltine, Phys. Fluids 17, 961 (1974) and Y. B. Kim, P. H. Diamond, and R. J. Groebner, Phys. Fluids B 3, 2050 (1991)]. The results from all three models are in fair agreement. Furthermore, the electric field has been deduced using the same models both with and without biasing the divertor plates relative to the machine wall, showing an inward propagation of the effect of the biasing created in the scrape-off layer (SOL). Undeniably, the electric field has been modified well inside the separatrix (0.6 less than or similar to r/a less than or similar to 0.9), revealing the possibility of modifying the internal electric field by external means. (C) 1997 American Institute of Physics.