Characterizations of Low-Frequency Zonal Flow in the Edge Plasma of the HL-2A Tokamak

TLDR

A low‑frequency (<4 kHz) axisymmetric potential structure with a radial coherence length below 1 cm is observed in the HL‑2A tokamak edge plasma. These observations match the predicted low‑frequency zonal flows, which propagate both inward and outward, coexist with the geodesic acoustic mode, and modulate GAM and turbulence in‑phase and antiphase, respectively.

Abstract

A low-frequency (<4 kHz), poloidally and toroidally symmetrical potential structure that peaks near zero frequency is observed in the edge plasma of the HL-2A tokamak. The axisymmetry structure exhibits a radial coherence length less than 1 cm. These characteristics are consistent with the theoretically predicted low-frequency zonal flows (LFZF). The radial wave-number frequency spectra of the LFZF show that the LFZF packets propagate both outwards and inwards. The geodesic acoustic mode (GAM) is found to coexist with the LFZF, and the LFZF is found to modulate the GAM and ambient turbulence with in-phase and antiphase relations, respectively, through an envelope analysis.