Acoustic mode driven by fast electrons in TJ-II Electron Cyclotron Resonance plasmas
Laboratorio Nacional de Fusión, Ciemat - 28040-Madrid, Spain
Received: 9 May 2016
Accepted: 9 August 2016
Intense harmonic oscillations in radiation signals are commonly observed during Electron Cyclotron Resonance (ECR) heating in TJ-II stellarator plasmas at low line-averaged electron density, . The frequency agrees with acoustic modes. The poloidal modal structure is compatible with Geodesic Acoustic Modes (GAM) but an toroidal structure is detected. The modes are found in the proximity of low-order rationals of the rotational transform ( in this work) and are excited by fast-electron populations, but they disappear at the onset of -islands rotation.
PACS: 52.35.Fp – Electrostatic waves and oscillations (e.g., ion-acoustic waves) / 52.55.Hc – Stellarators, torsatrons, heliacs, bumpy tori, and other toroidal confinement devices / 52.35.Py – Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
© EPLA, 2016