Alfvénic high-frequency oscillations at the pedestal of JET plasmas
Abstract
Long-lived (∼ 10 s) high-frequency oscillations (HFOs, 50−450 kHz) near the plasma edge have been reported and experimentally described in L-H transition studies at JET and AUG. In this work, we show that these HFOs are a general phenomenon observed in various plasma scenarios and compositions (H1, D, D-He3, D-T) under different heating schemes, including pure Ohmic, ICRH and NBI. We demonstrate that dominant axisymmetric (n=0) HFOs are Global Alfvén eigenmodes (GAEs) tied to the shear-Alfvén continuum (SAC) minima arising at the plasma edge due to the sharp decrease of the density and increase of the safety factor. This hypothesis is corroborated by the remarkable agreement found between the measured frequencies of HFOs and the SAC minima computed by the ideal MHD code CSMISH for a comprehensive set of JET pulses. This result, along with the fact that HFOs are observed over long time windows and across a variety of plasma scenarios, makes them convenient MHD constraints for accurate equilibrium reconstruction near the edge. In view of this pragmatic application, we derive a first-order analytic expression for the two lowest coupled branches of the n=0 SAC, disclosing their dependence (and, consequently, that of the HFOs) on the plasma density, safety factor, and elongation profiles. In addition, we discuss the nature of n≠ 0 HFOs observed along with the dominant n=0 HFOs.
Related
- Electrostatic high-frequency oscillations in partially ionized two-fluid plasmas
- Testing charged bumblebee black holes through high-frequency quasi-periodic oscillations in X-ray binaries
- Joint Constraints on Quantum Oppenheimer--Snyder Black Holes from High-Frequency Quasi-Periodic Oscillations in X-ray Binary Systems and the S2 Star Orbit
- One Component Plasmas Frequency Moments from the ISF
- A Minimal Self-Consistent Model for the Nonlinear Dynamics of Asymmetric Capacitively Coupled Radio-Frequency Plasmas
BibTeX
@misc{roque2026alfvénic,
title = {{Alfvénic high-frequency oscillations at the pedestal of JET plasmas}},
author = {Leonor Roque and Paulo Rodrigues and Emilia R. Solano and JET contributors and The Eurofusion Tokamak Exploitation Team},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.28193},
eprint = {2609.28193},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.28193},
}
RIS
TY - UNPB
TI - Alfvénic high-frequency oscillations at the pedestal of JET plasmas
AU - Leonor Roque
AU - Paulo Rodrigues
AU - Emilia R. Solano
AU - JET contributors
AU - The Eurofusion Tokamak Exploitation Team
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.28193
UR - https://arxiv.org/abs/2609.28193
AB - Long-lived (∼ 10 s) high-frequency oscillations (HFOs, 50−450 kHz) near the plasma edge have been reported and experimentally described in L-H transition studies at JET and AUG. In this work, we show that these HFOs are a general phenomenon observed in various plasma scenarios and compositions (H^1, D, D-He^3, D-T) under different heating schemes, including pure Ohmic, ICRH and NBI. We demonstrate that dominant axisymmetric (n=0) HFOs are Global Alfvén eigenmodes (GAEs) tied to the shear-Alfvén continuum (SAC) minima arising at the plasma edge due to the sharp decrease of the density and increase of the safety factor. This hypothesis is corroborated by the remarkable agreement found between the measured frequencies of HFOs and the SAC minima computed by the ideal MHD code CSMISH for a comprehensive set of JET pulses. This result, along with the fact that HFOs are observed over long time windows and across a variety of plasma scenarios, makes them convenient MHD constraints for accurate equilibrium reconstruction near the edge. In view of this pragmatic application, we derive a first-order analytic expression for the two lowest coupled branches of the n=0 SAC, disclosing their dependence (and, consequently, that of the HFOs) on the plasma density, safety factor, and elongation profiles. In addition, we discuss the nature of n≠ 0 HFOs observed along with the dominant n=0 HFOs.
ER -