Sensitivity of alpha-particle-driven Alfven eigenmodes to q-profile variation in ITER scenarios

TL;DR

This paper investigates how small variations in the magnetic q-profile in ITER scenarios significantly affect the stability and characteristics of alpha-particle-driven Alfven eigenmodes, highlighting challenges in predicting plasma behavior.

Contribution

It introduces a perturbative hybrid ideal-MHD/drift-kinetic approach to analyze the sensitivity of Alfven eigenmodes to q-profile changes in ITER scenarios.

Findings

Small (1%) changes in q-profile cause large shifts in eigenmode growth rates and locations.

Low magnetic shear in ITER scenarios increases sensitivity of eigenmodes to equilibrium variations.

Predicting alpha-particle transport is complicated by this high sensitivity.

Abstract

A perturbative hybrid ideal-MHD/drift-kinetic approach to assess the stability of alpha-particle-driven Alfven eigenmodes in burning plasmas is used to show that certain foreseen ITER scenarios, namely the Ip = 15 MA baseline scenario with very low and broad core magnetic shear, are sensitive to small changes in the background magnetic equilibrium. Slight variations (of the order of 1%) of the safety-factor value on axis are seen to cause large changes in the growth rate, toroidal mode number, and radial location of the most unstable eigenmodes found. The observed sensitivity is shown to proceed from the very low magnetic shear values attained throughout the plasma core, raising issues about reliable predictions of alpha-particle transport in burning plasmas.