Blobs on the High Field Side of Tokamaks

抄録

Turbulence-induced high density filaments, blobs, might represent the new paradigm for radial convective transport in the Scrape-Off-Layer of magnetic fusion devices. Models for individual blob dynamics, considering their generation on the Low Field Side (LFS) of the torus have been put forward. We investigate the existence of blobs in the peripheral region of the High Field Side (HFS) of the FT-2 tokamak. Langmuir probe measurements are used to detect and characterize blobs. The results were obtained in plasmas with enhanced Lower Hybrid Heating and data was acquired with a new fast data acquisition system with 50 MHz sampling rate. While the majority of the blobs are observed to move towards the wall as expected, some are observed to move inwards towards the core. This effect is not understood in the light of existing models for the LFS where only the outward direction is expected. Further characterization of plasma blobs should therefore involve both HFS and LFS. This could be done at ASDEX Upgrade where reflectometry systems are capable of measuring simultaneously the density turbulence on both HFS and LFS. The dependence between radial velocity, size and density of the blobs is also investigated.