Mesoscale electric fluctuations interacting with zonal flows, magnetic fluctuations and turbulence

Abstract

New mesoscale electric fluctuations (MSEFs) are identified in the edge plasmas of the HL-2A tokamak using multiple Langmuir probe arrays. The MSEFs, resulting from the synchronization and having components of dominant GAM and m/n=6/2 potential fluctuations, are found at the same frequency as that of the magnetic fluctuations of m/n=6/2 (m and n are poloidal and toroidal mode numbers, respectively). The temporal evolutions of the MSEFs and the magnetic fluctuations clearly show the frequency entrainment and the phase lock between the GAM and the m/n=6/2 magnetic fluctuations. The results indicate that GAMs and magnetic fluctuations can transfer energy through nonlinear synchronization. The nonlinear coupling analyses show that the MSEFs couple to turbulence and low frequency zonal flows (LFZFs). This suggests that the MSEFs may contribute to the LFZF formation, reduction of turbulence level, and thus confinement regime transitions. The analysis 2 of the envelope modulation demonstrates that both the MSEFs and the LFZFs modulate the turbulence while the MSEFs are modulated by the LFZFs.

Geodesic acoustic modes in magnetic confinement devices

“…This is discussed later in section 15.2. Other work from the Hefei/SWIP groups includes radial profiles of b 2 Σ ( f GAM ) [354], I-phase and bispectrum [356,533], as well as many papers by Zhao [345,353,476,534,535] and others [346].…”

“…The entrainment of an edge (m/n = 0/0) natural GAM with an applied (m/n = 6/2) static RMP magnetic field has been studied in HL-2A ECR heated L-mode plasmas. Using multiple arrays of multi-pin LPs and magnetic Mirnov coils, a strong f ≈ 10.5 kHz GAM in V f fluctuations was observed, together with an (m/n = 6/2) potential mode, (so-called meso-scale electric field fluctuations (MSEFs)), plus an (m/n = 6/2) magnetic perturbation, all oscillating at the same 'GAM' frequency [352,353]. Toroidally separated LPs confirm the GAM n = 0 ± 0.2 and finite k r = 3.5 ± 0.2 cm −1 zonal structure (poloidal m number not given), while cross correlation of probe V f (close to the GAM spatial peak) and magnetic signals from a toroidal array of 10 Mirnov coils show a clear m/n = 6/2 structure at the q = 3 surface.…”

Temporal-spatial structures of plasmas flows and turbulence around tearing mode islands in the edge tokamak plasmas

“…The NTMinduced islands modulate den sity fluctuations in the core plasmas [22]. Synchronization of magnetic islands and geodesic acoustic modes (GAMs), a new mechanism of coherent structure formation is found in the edge tokamak plasmas [23,24]. Although the importance of mutual interaction between turbulent fluctuations and magn etic islands has been widely recognized, quadrupole structures of the flows and the radially elongated flow formation in the vicinity of magnetic islands have not been reported.…”

A brief review: experimental investigation of zonal flows and geodesic acoustic modes in fusion plasmas

“…The LFZF driven possibly from quasi-coherent structures is suggested by the observation of the LFZF modulation on GAMs in the HL-2A tokamak [32]. Recently, the coupling of the mesoscale electric fluctuations (MSEFs) and LFZFs was detected with ECRH heating in HL-2A [81,82]. The applied ECRH power is up to 500 kW and the probe is in the radial position of Δr∼−4.2 cm inward from the LCFS.…”