Results from the Alfv\'{e}n Eigenmode Active Diagnostic during the 2019-2020 JET deuterium campaign

TL;DR

This paper analyzes the excitation and damping of Alfvén Eigenmodes in JET during 2019-2020, providing detailed measurements and trends that inform future plasma experiments and understanding of mode physics.

Contribution

It presents a comprehensive analysis of Alfvén Eigenmode excitation, damping, and mode characteristics during the JET deuterium campaign, including new empirical data and observed trends.

Findings

Resonant frequencies range from 30 to 250 kHz.

Good agreement between observed and calculated mode numbers.

Resonance detection probability decreases with plasma current.

Abstract

This paper presents results of extensive analysis of mode excitation observed during the operation of the Alfv\'{e}n Eigenmode Active Diagnostic (AEAD) in the JET tokamak during the 2019-2020 deuterium campaign. Six of eight toroidally spaced antennas, each with independent power and phasing, were successful in actively exciting stable MHD modes in 479 plasmas. In total, 4768 magnetic resonances were detected with up to fourteen fast magnetic probes. In this work, we present the calculations of resonant frequencies $f_0$, damping rates $\gamma < 0$, and toroidal mode numbers $n$, spanning the parameter range $f_0 \approx$ 30 - 250 kHz, $-\gamma \approx$ 0 - 13 kHz, and $\vert n \vert \leq 30$. In general, good agreement is seen between the resonant and the calculated toroidal Alfv\'{e}n Eigenmode frequencies, and between the toroidal mode numbers applied by the AEAD and estimated of the excited resonances. We note several trends in the database: the probability of resonance detection decreases with plasma current and external heating power; the normalized damping rate increases with edge safety factor but decreases with external heating. These results provide key information to prepare future experimental campaigns and to better understand the physics of excitation and damping of Alfv\'{e}n Eigenmodes in the presence of alpha particles during the upcoming DT campaign, thereby extrapolating with confidence to future tokamaks.