THEORETICAL TRANSPORT MODELING OF OHMIC COLD PULSE EXPERIMENTS

The response of several theory-based transport models in Ohmically hea ted tokamak discharges to rapid edge cooling due to trace impurity inj ection is studied. Results are presented for the Institute for Fusion Studies-Princeton Plasma Physics Laboratory (IFS/PPPL), gyro-Landau-fl uid (GLF23), Multi-mode (MM), and the Itoh-Itoh-Fukuyama (IIF) transpo rt models with an emphasis on results from the Texas Experimental Toka mak (TEXT) [K. W. Gentle, Nucl. Technol./Fusion 1, 479 (1981)]. It is found that critical gradient models containing a strong ion and electr on temperature ratio dependence can exhibit behavior that is qualitati vely consistent with experimental observation while depending solely o n local parameters. The IFS/PPPL model yields the strongest response a nd demonstrates both rapid radial pulse propagation and a noticeable i ncrease in the central electron temperature following a cold edge temp erature pulse (amplitude reversal). Furthermore, the amplitude reversa l effect is predicted to diminish with increasing electron density and auxiliary heating in agreement with experimental data. An Ohmic pulse heating effect due to rearrangement of the current profile is shown t o contribute to the rise in the core electron temperature in TEXT, but not in the Joint European Tokamak (JET) [A. Tanga and the JET Team, i n Plasma Physics and Controlled Nuclear Fusion Research 1986 (Internat ional Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 65] and the Toka mak Fusion Test Reactor (TFTR) [R. J. Hawryluk, V. Arunsalam, M. G. . Bell et al., in Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 51 ]. While this phenomenon is not necessarily a unique signature of a cr itical gradient, there is sufficient evidence suggesting that the appa rent plasma response to edge cooling may not require any underlying no nlocal mechanism and may be explained within the context of the intrin sic properties of electrostatic drift wave-based models. (C) 1998 Amer ican Institute of Physics. [S1070-664X(98)01811-4].