Existence of discrete modes in an unstable shear Alfvén continuous spectrum

Abstract

In this letter, we demonstrate the existence of unstable ion temperature gradient driven Alfvén eigenmodes in tokamak plasmas, which are ideally stable with respect to magnetohydrodynamics (MHD). Conditions for the destabilization of such modes are quantitatively discussed on the basis of theoretical analyses of the mode dispersion relation, which is given in a compact analytical form. It is emphasized that instability requires both sufficiently strong thermal ion temperature gradients and that the plasma be sufficiently close to ideal MHD marginal stability.

Observation of Low Frequency MHD Mode Driven by Energetic Particles in Large Helical Device Plasmas with Strong Interchange Mode Activities

“…The BAEs occur in the low-frequency kinetic thermal ion (KTI) gap in the shear Alfvén wave (SAW) continuous spectrum [11]. The stability mechanism of BAE is more complex than toroidal Alfvén eigenmodes (TAE) because the many kinetic effects play crucial roles in the mode excitation, saturation or damping [12][13][14]. The effects include the ion diamagnetic drift, thermal ion compression, finite Larmor radius (FLR), finite orbit width (FOW), and energetic-particle effects, and so on.…”

“…The BAE excitation can be described using the generalized fishbone-like dispersion relation (GFLDR) [13,14,16]. The GFLDR developed by L. Chen & F. Zonca is used to study plasma dynamics with the frequency range from kinetic ballooning mode (KBM)/BAE to TAE.…”

Linear dispersion relation of beta-induced Alfvén eigenmodes in presence of anisotropic energetic ions

“…Significant efforts, both experimental and theoretical, has been dedicted to this topic [2,[6][7][8][9][10][11]. Beta-induced Alfvén eigenmodes (BAEs) are particularly important since they can strongly interact with both thermal ions and EPs [5,[12][13][14][15][16].…”

Drift-sound and drift-Alfvén eigenmodes in toroidal plasmas

“…[20] for the case of ω > ω * and ω > c ei /R; a more general expression for α can be found in ref. [21]). …”