Microwave imaging reflectometry in LHD

Yamaguchi

Shi

et al. 2008

Microwave imaging reflectometry (MIR) was developed in TPE-RX, one of the world's largest reversed field pinch (RFP) devices. The system optics are made of aluminum mirrors, Teflon lenses, and Plexiglas plates in order to reduce size. In this system, frequencies are stabilized so that noise can be reduced using narrow bandpass filters. A 4×4 2-D mixer array and phase detection system have also been developed. With this system, density fluctuations in the high-Θ RFP plasma, pulsed poloidal current drive (PPCD) plasma, and quasi-single helicity (QSH) plasma are observed in TPE-RX. This is the first MIR experiment in an RFP device.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microwave Imaging Reflectometry Experiment in TPE-RX

Yamaguchi

Shi

et al. 2008

“…Microwave imaging reflectometry (MIR) has been applied to the Large Helical Device (LHD) and TPE-RX [1,2]. This technology is based upon the reflection of microwaves at the density-dependent cutoff layer, and the fluctuating phase of the reflected wave is dominated by the density fluctuation close to the cutoff layer.…”

Section: Introductionmentioning

confidence: 99%

Data Analysis Techniques for Microwave Imaging Reflectometry

Shi

Yamaguchi

et al. 2008

Self Cite

A data analysis technique for microwave imaging reflectometry (MIR) in the Large Helical Devices (LHD) and TPE-RX plasmas has been investigated. In LHD, the fast Fourier transform (FFT) is employed. The statistical properties of the fluctuation spectra on MIR signals are quantified by the time-frequency analysis by the ensemble average technique. Statistical analyses using cross-correlation and coherence spectra reveal the characteristics of MHD modes, such as wave numbers, mode numbers, and phase velocity. In TPE-RX, the wavelet analysis is more useful because the phenomena are transient in TPE-RX plasma.

“…In the Large Helical Device (LHD), a prototype MIR system with three commercial horn antennas, has successfully received scattered microwaves from plasmas [2,3]. The received microwaves were transmitted from the receiver antenna to mixer components remote from the diagnostic port by oversized waveguides.…”

mentioning

confidence: 99%

“…Microwave imaging reflectometry (MIR) would be a sensitive fluctuation diagnostics in turbulent plasmas. MIR is a multi-receiver reflectometry that can potentially visualize the 3-D structures of electron density fluctuations by projecting images of the cutoff surfaces onto the image focal plane [1].In the Large Helical Device (LHD), a prototype MIR system with three commercial horn antennas, has successfully received scattered microwaves from plasmas [2,3]. The received microwaves were transmitted from the receiver antenna to mixer components remote from the diagnostic port by oversized waveguides.…”

mentioning

confidence: 99%

Optics Design for Microwave Imaging Reflectometry in LHD

Yoshinaga

Kuwahara

et al. 2010

An optics system for microwave imaging reflectometry (MIR) in the Large Helical Device (LHD) was newly developed to optimize the performance of the two-dimensional microwave receiver array. Reflected microwaves from the plasma and the first local oscillator (LO) wave are transmitted to the receiver array via the optics from the front. Finite-difference time-domain (FDTD) calculation was used to design the ellipsoidal or hyperboloidal shapes of the quasi-optical mirrors. It is confirmed that the LO beam in the constructed system covers the receiver antenna aperture area as intended. The S/N ratios of the signals are improved with this optimized optics system from those in the previous system. Understanding confinement and transport in magnetically confined plasmas is one of the important issues for realizing fusion reactor. Microscale instabilities such as turbulence are considered to activate anomalous transport. Microwave imaging reflectometry (MIR) would be a sensitive fluctuation diagnostics in turbulent plasmas. MIR is a multi-receiver reflectometry that can potentially visualize the 3-D structures of electron density fluctuations by projecting images of the cutoff surfaces onto the image focal plane [1].In the Large Helical Device (LHD), a prototype MIR system with three commercial horn antennas, has successfully received scattered microwaves from plasmas [2,3]. The received microwaves were transmitted from the receiver antenna to mixer components remote from the diagnostic port by oversized waveguides. In a full-scale imaging system, however, it is difficult to use waveguides to transmit received signals from dozens of receiver channels. This signal transmission problem was solved by a newly developed 2-D horn-antenna mixer array (HMA), which consists of arrayed quasi-optical antenna-mixers covered with pyramidal horn apertures [4,5]. This HMA was developed to down-convert received microwaves into intermediate frequency (IF) signals by Schottky diodes, which are placed inside each of the HMA apertures. After downconversion, the signal handling becomes very convenient, since printed circuit boards or ordinary coaxial cables can be used for amplification, filtering, or transmission. This paper presents the methodology for mixing the received microwave signal with the first local oscillator (LO) signal for down-conversion. Our technique is to cast the LO microwave (55.8 GHz) from the front of the HMA aperture together with the received microwave signals. The status of the optics system for LO wave projection is also described.The newly designed optics system for MIR in LHD is illustrated in Fig. 1. It consists of aluminum alloy mirrors