Scrape-Off Layer Properties of Single-Null and Snowflake Diverted Plasmas in TCV

摘要

The snowflake (SF) divertor [1, 2] is an innovative solution-to reduce plasma-wall interaction by acting on the magnetic field topology to improve the divertor action. In this configuration, both the poloidal magnetic field and its spatial first derivatives vanish at the null point. The separatrix divides the poloidal plane in six regions and, as a consequence, the configuration has four divertor legs. Compared to a Single-Null (SN) configuration, the snowflake configuration is characterized by a larger flux expansion around the null point, a longer connection length in the scrape-off layer (SOL) and a larger magnetic shear close to the separatrix. These properties are expected to affect the local heat load on the divertor plates, in particular during Edge Localized Modes (ELMs). In the first part, we estimate, from Langmuir probe (LP) measurements, the heat loads during ELMy H-mode SN and SF plasmas. In, the secqnd part, we report on, statistical properties of SOL fluctuations measured with LP and a fast imaging camera.