ECEI on DIII-D

System Overview

Fig 1: ECEI setup in DIII-D

The Electron Cyclotron Emission Imaging diagnostic had been commissioned on the DIII-D tokamak (San Diego, CA) since 2010. Dual detector arrays provide simultaneous two-dimensional images of Te fluctuations over radially distinct and reconfigurable regions, each with both vertical and radial zoom capability. A total of 320=20 vertical x 16 radial channels (range from 75 -140 GHz) are available. The experimental results show that the acquisition of coherent electron temperature fluctuations can be as low as 0.1% with excellent clarity and spatial resolution.

Fig 2: Imaging of Alfvén eigenmodes on DIII-D illustrates significant improvements in the ECEI diagnostic technique

Fig 3: A sawtooth crash exhibiting complete reconnection is imaged on DIII-D with unprecedented clarity.

Physics Results:

Since the commissioning of ECE-Imaging instrument on the DIII-D tokamak in 2010, many exciting physics results have been obtained, from identity of sawtooth precursor oscillations (Fig 4), to good match between observed Alfven instabilities eigenmode on DIII-D with modeling in numerical (Fig 5-6), to the identification of phase locking of magnetic islands (Fig 7), to the study of edge harmonic osillations (Fig 8-9), etc.

Fig 4: Two distinct m/n = 1/1 electron temperature perturbations are identified during the sawtooth ramp. The normalized electron temperature of each poloidal mode is reconstructed under an approximation rigid-body rotation in (a) and (b). When the contribution of slow (∼15-Hz) electron temperature profile evolution is removed, as in the corresponding plots in (c) and (d), the 2-D temperature fluctuations are found to be indistinguishable. The complete instantaneous view of an ECEI array is overlaid in (d) for reference.

Fig 5: A reversed shear induced Alfven eigenmode (RSAE) observed on DIII-D is compared to modeling in numerical eigenmode solvers. (a) In an ideal-MHD approximation, the n = 4 RSAE is predicted at 65 kHz for the experimentally obtained thermal plasma equilibrium. (b) A non-perturbative hybrid gyrofluid-MHD model implemented by TAEFL reproduces the same mode, but includes a distortion also observed by ECEI (c).

Fig 6: Eigenmode structures for three RSAEs excited near t = 550 ms are captured with ECEI and compared to simulated mode structures obtained with NOVA. The color bar given is applicable to the measured data from ECEI, while simulated modes are plotted on a normalized scale. The modes in (a) and (c) show a ‘‘fundamental’’ radial mode structure with a single maximum in the radial mode envelope. The mode shown in (b) exhibits a radial null in the fluctuation amplitude and is identified as the first radial harmonic of the n = 3 mode shown in (a).

Fig 7: (a) A spectrogram of magnetic fluctuations. Coalescence of 3/2 and 4/2 island frequencies occurs near t = 2580 ms. (b) and (c) Bicoherence estimates before and after phase-locking. (d) and (e) Local phase velocities near ρ = 0.4, measured by ECE-imaging.

Fig 8:Real (a) and imaginary (b) components of an n = 1 EHO, imaged by Fourier filtering techniques, from shot #145049, t = 2.708 s. Optically thick channels are mapped to the mean position of origin of the emission, as calculated using the synthetic diagnostic, while other data remains mapped to cold resonances. The solid contour marks ρ = 0.95, the outer boundary of the optically thick region for this case.

Fig 9: Comparison between M3D-C1 simulation (a), synthetic ECEI response (b), and ECEI measurement (c) of electron temperature fluctuations of an EHO (DIII-D, shot #157102 at 2420 ms).

Highlighted Innovations:

Recently new horn array with System-on-Chip solution for ECEI diagnostic has developed and fabricated for DIII-D. The upgraded system is designed for improved sensitivity and enhanced EMI shielding to improve SNR for ELM imaging and thus has better shielding against RF heating and noise, greatly reduced noise temperature and compact system size. More details on System-on-Chip (SoC) solution can be found here.

Fig 10: System-on-Chip Based Horn Array for DIII-D

Selected Publications

Zhu, Yilun, et al. "New Trends in Microwave Imaging Diagnostics and Application to Burning Plasma." IEEE Transactions on Plasma Science 47.5 (2019): 2110-2130.
Chen, Ming, et al. "Experimental characterization of the effect of E× B shear on edge-harmonic oscillation mode structure." Plasma Physics and Controlled Fusion 61.8 (2019): 085003.
Taimourzadeh, S., et al. "Verification and validation of integrated simulation of energetic particles in fusion plasmas." Nuclear Fusion 59.6 (2019): 066006.
Zhu, Y., et al. "Liquid crystal polymer receiver modules for electron cyclotron emission imaging on the DIII-D tokamak." Review of Scientific Instruments 89.10 (2018): 10H120.
Y. Wang et al., "Millimeter-wave imaging of magnetic fusion plasmas: technology innovations advancing physics understanding", Nuclear Fusion, Volume 57, Number 7
B. Tobias, M.Chen et al., "Rotation profile flattening and toroidal flow shear reversal due to the coupling of magnetic islands in tokamaks", Physics of Plasmas 23, 056107 (2016)
L. Shi et al., "Synthetic diagnostics platform for fusion plasmas (invited)",Review of Scientific Instruments 87, 11D303 (2016)
B. Tobias et al., "Phase-locking of magnetic islands diagnosed by ECE-imaging", Review of Scientific Instruments 85, 11D847 (2014)
B. Tobias et al., "ECE-imaging of the H-mode pedestal (invited)", Review of Scientific Instruments 83, 10E329 (2012)
B. Tobias et al., "Sawtooth precursor oscillations on DIII-D", IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 11, NOVEMBER 2011
B. Tobias et al., "Commissioning of electron cyclotron emission imaging instrument on the DIII-D tokamak and first data", Review of Scientific Instruments 81, 10D928 (2010)

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