Formation, stability and momentum transport characteristics of impurity-induced snakes in Alcator C-Mod

摘要

A small but long-lived helical perturbation dubbed a snake was first found at JET following the injection of a high-speed frozen deuterium pellet [1]. More than two decades have passed since their discovery and observation in every major fusion facility. However, the description of the snake formation, stability criteria as well as its impact on the background plasma has remained elusive. The role of impurity density, resistivity, collisionality and momentum exchange with the background plasma can now be described using an adequate suite of spectroscopic diagnostics that included AXUV bolometers, SXR tomography and a high-resolution x-ray crystal imaging spectrometer [2].