Predict-first experiments and modeling of perturbative cold pulses in the DIII-D tokamak

Cold pulses are introduced in Ohmic DIII-D tokamak plasmas via injection of impurities with a laser blow-off system, revealing for the first time in this machine a quick increase in core electron temperature shortly after the edge cold-pulse injection at low collisionality. The experi- mental results are consistent with predict-first simulations of heat transport enabled by the Trapped Gyro-Landau-Fluid transport model. Measurements of electron density evolution during the cold-pulse propagation are enabled by a high time resolution density profile reflec- tometer. The density evolution reveals the quick propagation of a pulse from edge to core, which is a mechanism to transiently increase core temperature in low-collisionality plasmas. Local transport simulations with measured density evolution demonstrate that the core tempera- ture response can indeed be explained by the stabilization of Trapped Electron Mode turbulence at low collisionality, thus providing confi- dence that local transport modeling is enough to explain cold-pulse propagation and associated phenomenology.