A SELF-CONSISTENT MODEL FOR LOW-HIGH TRANSITIONS IN TOKAMAKS

A system of equations that couples the rapidly varying fluctuations of resistive ballooning modes to the slowly varying transport of the den sity, vorticity and parallel momentum have been derived and solved num erically. Only a single toroidal mode number is retained in the presen t work. The low-mode (L-mode) phase consists of strong poloidally asym metric particle transport driven by resistive ballooning modes, with l arger flux on The outboard side compared to the inboard side. With the onset of shear flow driven by a combination of toroidal drive mechani sms as well as the Reynolds stress, the fluctuations associated with t he resistive ballooning modes are attenuated leading to a strong reduc tion in the particle transport. The drop in the particle transport res ults in steepening of the density profile leading to the high-mode (H- mode). (C) 1996 American Institute of Physics.