Electron Cyclotron Emission Imaging on the EAST Tokamak

An upgraded electron cyclotron emission imaging （ECEI） system consisting of new optics lenses with necessary electronics for receiving and processing signals for two dimension （2D） ECEI diagnostics was installed on EAST. Hyperboloid lens were adopted in the new system to optimize the spatial resolutions. The mixers array of sixteen elements measured the plasma electron cyclotron emission at eight frequencies simultaneously, and the profiles of the electron temperature and its fluctuation in an area of 20 cm （vertical） × 6 cm （horizontal） could then be analyzed. Evolution of sawtooth precursor and crash in EAST was observed.

Electron temperature fluctuation in the HT-7 tokamak plasma observed by electron cyclotron emission imaging

The fluctuation of the electron temperature has been measured by using the electron cyclotron emission imaging in the Hefei Tokamak-7 （HT-7） plasma. The electron temperature fluctuation with a broadband spectrum shows that it propagates in the electron diamagnetic drift direction, and the mean poloidal wave-number kθ is calculated to be about 1.58cm^-1, or k^-θρs ≈ 0.34. It indicates that the fluctuation should come from the electron drift wave turbulence. The linear global scaling of the electron temperature fluctuation with the gradient of electron temperature is consistent with the mixing length scale qualitatively. Evolution of spectrum of the fluctuation during the sawtooth oscillation phases is investigated, and the fluctuation is found to increase with the gradient of electron temperature increasing during most phases of the sawtooth oscillation. The results indicate that the electron temperature gradient is probably the driver of the fluctuation enhancement. The steady heat flux driven by electron temperature fluctuation is estimated and compared with the results from power balance estimation.

One-Dimensional Vertical Electron Cyclotron Emission Imaging Diagnostic for HT-7 Tokamak

At the first stage of the electron cyclotron emission imaging （ECEI） diagnostic project on HT-7, a 16-channel vertical-resolved ECEI diagnostic has been developed and installed on HT-7 tokamak to measure electron cyclotron emission with a temporal resolution of 0.5 usec. The system works at a fixed frequency of 97.5 GHz. The sample volumes of the system are aligned vertically with a vertical channel spacing of 11 mm, and can be shifted across the plasma cross-section by varying the toroidal magnetic field. The high spatial resolution of the system is achieved by utilizing a low-cost linear mixer/receiver array and an optical imaging system. The focus location may be shifted horizontally when translating one of the optical imaging elements. The details of the system design and laboratory testing of the ECEI optics are presented together with the preliminary experimental results.

Electron Cyclotron Emission Imaging Observations of m/n=1/1 and Higher Harmonic Modes during Sawtooth Oscillation in ICRF Heating Plasma on EAST

The m/n = 1/1 and its higher harmonic modes are observed in sawtooth oscillations by using the novel high- resolution 2D ECE imaging system on the experimental advanced superconducting Tokamak （EAST）. Higher harmonic modes are appearing for a short time during the crash phase of sawtooth oscillation in lower βp plasma, which is not the preferabie position in the poloidal cross section. These modes generate sharp pressure points on the inversion radius during the crash phase of sawtooth oscillation. Furthermore, reconnection events proceed in two distinctive phases. In the first phase, a small amount of heat is expelled through the weak reconnection while in the second phase the remaining large quantity of heat and particles emerged rapidly from the hot core to the peripheral region of the inversion radius. In addition, these harmonic modes are only found before and after the ICRF pulse, while in the ICRF pulse only the （1,1） mode exists in the sawtooth oscillation.

A synthetic diagnostics platform for microwave imaging diagnostics in tokamaks

Interpreting experimental diagnostics data in tokamaks,while considering non-ideal effects,is challenging due to the complexity of plasmas.To address this challenge,a general synthetic diagnostics(GSD)platform has been established that facilitates microwave imaging reflectometry and electron cyclotron emission imaging.This platform utilizes plasma profiles as input and incorporates the finite-difference time domain,ray tracing and the radiative transfer equation to calculate the propagation of plasma spontaneous radiation and the external electromagnetic field in plasmas.Benchmark tests for classical cases have been conducted to verify the accuracy of every core module in the GSD platform.Finally,2D imaging of a typical electron temperature distribution is reproduced by this platform and the results are consistent with the given real experimental data.This platform also has the potential to be extended to 3D electromagnetic field simulations and other microwave diagnostics such as cross-polarization scattering.

Optical Design of ECEI Diagnostic System for HT-T Tokamak

Electron cyclotron emission imaging system in the frequency range of 95 GHz -125 GHz is going to be constructed for a two-dimensional diagnosis of the electron temperature profiles and fluctuations on the HT-7 Tokamak. The optical design for the ECEI diagnostic system is completed. Because of the superconducting technology used in HT-7, the vacuum chamber is rather thick (630 mm), the height of the horizontal windows is limited (maximum 450 mm), which constrains greatly the ECE imaging Gaussian beam that passing through the windows. We here comes to make a design compromise between the number of the beams that can pass through the windows and the spatial resolution (around 1.1 cm). We also find that due to the field curvature of the optical system, the gaussian beams of edge channels are always overlapped. To flatten the field curvature, it is needed to insert a concave made of a material with a low refractive index (compared with the one used in the convex). But the suitable material has not been available so far, therefore the deterioration of the resolution in some channels (e.g. the edge channels) is acceptable.