ECEI on HL-2A

UC Davis fabricated a 24x8 channel electron cyclotron emission imaging (ECEI) system for the Center for Fusion Science of the Southwestern Institute of Physics (SWIP) for use on the HL-2A tokamak in Chengdu, China.

The system is comprised of a front-end 24 channel imaging array with a tunable RF range spanning 90 to 135 GHz, and a set of back-end ECEI electronics that together generate 24x8 = 192 channel images of the 2nd harmonic X-mode ECE radiation emitted from the HL-2A plasma. Each channel corresponds to the received ECE power at a specific input frequency on a specific imaging array element, with an RF bandwidth of ~600 MHz, and a video bandwidth that can be remotely adjusted between 50 and 400 kHz. RF channel spacing, which determines the radial spacing between channels, is user-selectable between 600 and 900 MHz to match the ECEI radial coverage to particular physics experiments on HL-2A. The result is a time-resolved 2-D image of T_e profiles and T_efluctuations over an extended portion of the target plasma.

ECEI setup on HL-2A

Under the narrow zoom operation, the power spectrum is obtained at (a) in focus (b) out of focus at different focal locations.

The beam waist is (c) 1.3 cm under narrow zoom operation (d) 1.8 cm under wide zoom operation

The benchmark testing has been done with modeling in both narrow zoom and wide zoom condition: the measurements match well with the modeling results; the system's robustness is better under the wide zoom operation.

Physics Results

Evolution of the structure of the sawtooth crash precursor mode

The 2D structure of the sawtooth crash process has also been observed. Figures 7 and 8 illustrate the evolution of the mode structure before and during sawtooth crash phase, using the same color bar as shown in the right of Figure 8. As shown in Figure 7, there is one hot spot and one cold spot precessing near the q = 1 surfaces as marked by the dashed curves, which demonstrates m = 1. The mode precesses in the ion diamagnetic drift direction, and the mode structure takes on a crescent-like shape. During the crash phase, as shown in Figure 8, in the upper five frames, the mode can still be observed to precess near the q = 1 surface, but it seems that the mode structure is highly distorted. In the lower five frames, it can be seen that the hot spot transported outwards rapidly and is followed by the slow recovery of the core electron temperature. The reconnection process is fast and outside the q = 1 surface.

Related Recent Publications：

System:

M. Jiang et al., Rev. Sci. Instrum. 84, 113501 (2013);
Z. B. Shi, et al., Plasma and Fusion Research, 9, 3402123 (2014)
M. Jiang et al., Rev. Sci. Instrum. 86, 076107 (2015)
M. Jiang et al., Plasma Sci. Technol. 19 (2017) 084001

Physics:

L. M. Yu et al 2017 Nucl. Fusion 57 036023 (resonant kink mode)
M. Jiang et al., Phys. Plasmas 24, 022110 (2017) (double e-fishbone)
W. Chen et al 2016 Nucl. Fusion, 56 044001(nonlocal transport and fishbone)
W. Chen, M. Jiang et al., Nucl. Fusion 57 (2017) 114003 (mode coupling)
L. M. Yu et al, Journal of the Physical Society of Japan 86, 024501 (2017) (resonant kink mode)
P. W. Shi et al., PST, 2016 kink mode
M. Jiang et al. 2017 NF (multi-scale interaction between TM and turbulence)

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