Influence ofm / n= 2/1 magnetic islands on perpendicular flows and turbulence in HL-2A Ohmic plasmas

Abstract

The radial profiles of perpendicular flows in the presence of the magnetic island were firstly measured in the HL-2A tokamak by hopping the work frequency of the Doppler backward scattering reflectometer system along with a two-dimensional electron cyclotron emission imaging diagnostic identifying the island locations. It has been observed that across the O-point cut the perpendicular flow is quite small at the center of the island and strongly enhanced around the boundary of the island, resulting in a large increase of the flow shear in the outer half island, while across the X-point cut the flow is almost flat in the whole island region. Meanwhile it was found that the density fluctuations are generally weakened inside the island. The results indicate that both the perpendicular flow and the density fluctuation level are modulated by the naturally rotating tearing mode near the island boundary. The cross-correlation between the perpendicular flows and the oscillating electron temperature further reveals that the modulation of the perpendicular flow occurs mainly inside and in the vicinity of the island.

Development of ECE/ECEI diagnostics and MHD-related studies on HL-2A tokamak

“…ECEI is an advanced extension of the traditional ECE radiometry with the same basic principle; however, it can image the plasma onto a vertically aligned antenna array by using a set of quasi-optical lenses with the heterodyne frequency capability yielding 2D images. The ECEI diagnostic has been proven to be a powerful tool for MHD physics through electron temperature fluctuation measurements, providing invaluable images on core/edge physics [6][7][8][9][10][11]. The ECEI instrument includes four subsystems, i.e., quasi-optical system, antenna array, microwave receivers and digitizers.…”

“…In HL-2A, the ECEI diagnostic has been extensively used to detect the 2D structure of large scale MHD modes [10,11,15,16], such as tearing mode, fishbone, and sawtooth crash. Figure 7 shows the mode structure of the m/n=2/1 tearing mode.…”

Progress of microwave diagnostics development on the HL-2A tokamak

“…Three microwave interferometer systems are developed to measure the plasma line-averaged density and density fluctuations in the main plasma and divertor regions [22,23]. The multi-channel ECE and ECEI are developed to measure the electron temperature profiles and fluctuations [24][25][26][27][28][29][30]. Three frequency modulation continuous wave (FMCW) reflectometers and two amplitude modulation (AM) reflectometers are developed to measure the density profiles from low field side in the horizontal plane [31][32][33][34].…”

“…The features of electron heat transport in H-mode pedestal and long-range correlation of turbulence during nonlocal transport have been studied for the first time by using the new ECE system [8,[40][41][42][43]. Due to its high spatial resolution and local measurement, the locations of the MHD modes such as fishbone, tearing mode, and neoclassical tearing mode (NTM), and the turbulence transport inside the magnetic island, have been observed [27,44,45].…”

“…Microwave imaging diagnostic systems have made important contributions to plasma physics study and have been adopted at major fusion facilities worldwide [7,19]. The ECEI and MIR systems have been developed to visualize the two/threedimensional (2D/3D) density and temperature fluctuations on the HL-2A tokamak [12,[27][28][29][30]. The ECEI system is developed in collaboration with UC Davis [19,27,28].…”