Modeling of DIII-D Discharges With Feedback Control of the Safety Factor Profile Evolution
J.R. Ferron, P. Gohil, C.M. Greenfield, T.C. Luce, C.C. Petty, P.A. Politzer, M.R. Wade, V. Basiuk, F. Imbeaux, T.A. Casper, M. Murakami, Y. Ou, E. Schuster, Q. Gao, A. Wang,
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Philadelphia, Pennsylvania, October 30-November 3, 2006
Abstract
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Closed loop control of the q evolution is implemented by modifying the
rate of relaxation of the current density through changes in the
conductivity using neutral beam or electron cyclotron power for
electron heating. Comparisons between the experimental q evolution and
transport code (ONETWO, TRANSP, CRONOS, CORSICA) modeling are being
used to develop the physics model of the control process. We find that
the neutral beam current drive profile in the simulation must peak near
the mid-radius, instead of near the axis as predicted by NBCD theory,
in order for the predicted q evolution to match the experiment. Alfven
eigenmode type fluctuations observed in the experiment could have
provided a mechanism for fast ion transport. A simplified physics model
is being developed for use in design of a model-based q evolution
controller which will be tested in CRONOS simulations and in the
experiment.