Scrape-off layer ion temperature measurements at the divertor target during type III and type I ELMs in MAST measured by RFEA

TL;DR

This paper presents a new fast measurement technique using RFEA to determine ion temperatures during ELMs in MAST, aiding understanding of heat loads on divertor materials in fusion reactors.

Contribution

Introduction of the fast swept technique (FST) for rapid Ti measurements during ELMs in MAST, improving temporal resolution of ion temperature data.

Findings

FST enables faster Ti measurements during ELMs.

Ion temperatures during type I ELMs are characterized.

Implications for divertor material erosion are discussed.

Abstract

In future nuclear fusion reactors high heat load events, such as edge-localised modes (ELMs), can potentially damage divertor materials and release impurities into the main plasma, limiting plasma performance. The most difficult to handle are type I ELMs since they carry the largest fraction of energy from the plasma and therefore deposit the largest heat flux at the target and on first wall materials. Knowing the temperature of the ions released from ELM events is important since it determines the potential sputtering they would cause from plasma facing materials. To make measurements of Ti by retarding field energy analyser (RFEA) during type I ELMs a new operational technique has been used to allow faster measurements to be made; this is called the fast swept technique (FST).