A 2D electron cyclotron emission imaging (ECEI) system has been developed for measurement of electron temperature fluctuations in the HL-2A tokamak. It is comprised of a front-end 24 channel heterodyne imaging array with a tunable RF range spanning 75-110 GHz, and a set of back-end ECEI electronics that together generate 24 × 8 = 192 channel images of the 2nd harmonic X-mode electron cyclotron emission from the HL-2A plasma. The simulated performance of the local oscillator (LO) optics and radio frequency (RF) optics is presented, together with the laboratory characterization results. The Gaussian beams from the LO optics are observed to properly cover the entire detector array. The ECE signals from the plasma are mixed with the LO signal in the array box, then delivered to the electronics system by low-loss microwave cables, and finally to the digitizers. The ECEI system can achieve temporal resolutions of ~μs, and spatial resolutions of 1 cm (radially) and 2 cm (poloidally).

ECE Imaging (ECEI) systems have been installed and are presently operating on the KSTAR, DIII-D, ASDEX-UG, and HT-7 tokamaks. All are inherently 2-D systems, collecting second harmonic ECE radiation to form temporally-resolved localized T e images. System resolutions range from 16 × 8 (HT-7 and ASDEX-UG) to 20 × 16 (DIII-D) to 24 × 16 (KSTAR), with a spatial resolution as low as 1.0 cm (vertical) by 0.9 cm (radial), and with video bandwidths up to 400 kHz. Noise and drift performance of ECEI systems installed on KSTAR and DIII-D were significantly improved in 2011 with new zero bias detectors. This higher level of performance has resulted in new physics advances as ECEI is employed to visualize high temperature plasmas from the plasma edge (pedestal region) through the plasma core, with examples presented herein. In addition to these systems, a new expanded view ECEI system has been developed for the EAST tokamak that produces 24 × 16 T e images from a single imaging array and which is currently being commissioned.

Techniques for visualizing turbulent flow in nature and in the laboratory have evolved over half a millennium from Leonardo da Vinci's sketches of cascading waterfalls to the advanced imaging technologies which are now pervasive in our daily lives. Advancements in millimeter wave imaging have served to usher in a new era in plasma diagnostics, characterized by ever improving 2D, and even 3D, images of complex phenomena in tokamak and stellarator plasmas. Examples at the forefront of this revolution are electron cyclotron emission imaging (ECEI) and microwave imaging reflectometry (MIR). ECEI has proved to be a powerful tool as it has provided immediate physics results following successful diagnostic installations on TEXTOR, ASDEX-U, DIII-D, and KSTAR. Recent results from the MIR system on LHD are demonstrating that this technique has the potential for comparable impact in the diagnosis of electron density fluctuations. This has motivated a recent resurgence in MIR research and development, building on a prototype system demonstrated on TEXTOR, toward the realization of combined ECEI/MIR systems on DIII-D and KSTAR for simultaneous imaging of electron temperature and density fluctuations. The systems discussed raise the standard for fusion plasma diagnostics and present a powerful new capability for the validation of theoretical models and numerical simulations.

Microwave imaging reflectometry provides broad poloidal coverage as a density fluctuation measurement tool. 2D imaging systems are evaluated for DIII-D relevant conditions using a full-wave reflectometer code, FWR2D. Reasonable correlation of the synthetic diagnostic signal with density fluctuations at the plasma cutoff surface for a wide range of fluctuation parameters is evaluated and achieved for coherent oscillations; also the frequency spectra are compared for relevant fluctuations. The consequences of non-idealities inherent to imaging fluctuations away from the plasma midplane, where receiving antennas view the plasma cutoff at oblique angles, are evaluated for the optimization of these systems.

Observation of modes consistent with the trapped-electron mode (TEM) has been made using the electron cyclotron emission imaging (ECEI) diagnostic on the DIII-D tokamak. The new measurements enable the extraction of spectral properties, including poloidal dispersion relations. The spatially correlated radial structure shows qualitative consistency with radially global linear gyrokinetic simulations, using the poloidal wavenumber selected in a narrow frequency band in the ECEI data. Simulations of trapped-electron modes (TEM) driven by the electron temperature gradient yield phase velocities in close agreement with measurements. As found previously in the outer core of DIII-D L-Mode plasmas, the electron temperature fluctuation levels from nonlinear gyrokinetic simulations fall below experiment.