# Sub-microsecond temporal evolution of edge density during edge localized modes in KSTAR tokamak plasmas inferred from ion cyclotron emission

## TL;DR

This paper demonstrates that ion cyclotron emission (ICE) can be used as a high-resolution diagnostic tool to observe the rapid evolution of edge density during ELMs in KSTAR tokamak plasmas, based on kinetic simulations matching observed chirping patterns.

## Contribution

It introduces a novel method to infer edge density evolution during ELMs using ICE signals and kinetic simulations, providing unprecedented temporal resolution.

## Key findings

- ICE chirping correlates with edge density collapse during ELMs
- Kinetic simulations successfully match observed ICE features
- ICE provides a high-resolution diagnostic of edge plasma dynamics

## Abstract

Ion cyclotron emission (ICE) is detected during edge localised modes (ELMs) in the KSTAR tokamak at harmonics of the proton cyclotron frequency in the outer plasma edge. The emission typically chirps downward (occasionally upward) during ELM crashes, and is driven by confined 3MeV fusion-born protons that have large drift excursions from the plasma core. We exploit fully kinetic simulations at multiple plasma densities to match the time-evolving features of the chirping ICE. This yields a unique, very high time resolution diagnostic of the collapsing edge pedestal density.