Recent Advancements in Microwave Imaging Plasma Diagnostics

Abstract

Significant advances in microwave and millimeter wave technology over the past decade have enabled the development of a new generation of imaging diagnostics for current and envisioned magnetic fusion devices. Prominent among these are revolutionary microwave electron cyclotron emission imaging (ECEI), microwave phase imaging interferometers, imaging microwave scattering and microwave imaging reflectometer (MIR) systems for imaging T e and n e fluctuations (both turbulent and coherent) and profiles (including transport barriers) on toroidal devices such as tokamaks, spherical tori and stellarators. The diagnostic technology is reviewed, and typical diagnostic systems are analyzed. Representative experimental results obtained with these novel diagnostic systems are also presented. _______________________________________________________________________

Development and application of radar reflectometer using micro to infrared waves

“…Otherwise, interference of the scattered wavefront destructs the shape of phase close to the cut-off position, thus making difficult extraction of the information from the reflectometer signal. One of the possible ways to solve this problem is microwave imaging reflectometry (MIR) [31][32][33].…”

Determination of the heat diffusion anisotropy by comparing measured and simulated electron temperature profiles across magnetic islands

“…The electron temperature around the island is measured by TEXTOR's ECE-Imaging diagnostic [10] that consists of an array of 8 radial times 16 vertical channels, which are located around the outer mid-plane for this shot. Thermal noise intrinsic to any ECE measurement is suppressed by applying singular value decomposition (SVD) to the measured data array and keeping the 10 most significant eigenvector pairs.…”

“…The application of the method is demonstrated for a 2 /1 magnetic island triggered by the dynamic ergodic divertor (DED) coil set [8] in the TEXTOR tokamak [9]. The experimental electron temperature around the island, measured by ECE-Imaging (electron cyclotron emission imaging) [10], is compared to the numerical simulation results.…”

Simultaneous projection and detection system of four different frequencies for microwave imaging reflectometry in Large Helical Device

“…Microwave imaging reflectometry ͑MIR͒ is a multireceiver reflectometry diagnostics, which aims to reconstruct two-or three-dimensional ͑2D/3D͒ structures of density fluctuations in turbulent plasmas. 2,3 In a MIR system, the reflected microwave from a disturbed cutoff surface is focused onto the 2D receiver antenna array via imaging optics. 4,5 The 2D structure of the cutoff surface, which usually corresponds roughly to a magnetic surface, can be obtained with a single-frequency MIR system.…”

“…A downconversion scheme with mixer diodes mounted on microstrip antenna is similar to the previous works on MIR or electron-cyclotron emission imaging systems. 2,8,9 The advantages of utilizing the HMA are the ease of composing the 2D receiver array and the high gain ͑directionality͒ of its horn apertures. However, the imaging optics system becomes rather complicated since the reflected signal waves and the first LO must be simultaneously focused and projected onto the front of the horn aperture.…”