Abstract
A 90GHz W-band millimeter-wave back-scattering system is designed and installed for measuring electron scale turbulence (k⊥ρs ∼ 40). A metal lens relay antenna is used for in-vessel beam focusing, and a beam diameter of less than 40mm is achieved in the plasma core region. This antenna can be steered at an angle of 159° ± 6°, which almost covers the plasma radius. The estimated size of the scattering volume is ∼105mm at the edge and 135mm at the core, respectively. A 60m corrugated waveguide is used to achieve a low transmission loss of ∼8 dB. A heterodyne detection system for millimeter-wave circuits with probing power modulation can distinguish the scattered signal from background noise.
Highlights
Multi-scale turbulence interaction, especially, mixed micro-scale turbulence phenomena which includes both the ion and the electron scale turbulences, is of interest[1] in the high temperature plasma confinement study at present and there are many theoretical studies[2,3,4,5,6,7,8]
The electron density is higher than 1x1019m-3 in the usual LHD plasma experiments, the diagnostic region is almost in α >1. This means that the scattering signal is collective, and the scattering signal originates from correlated density fluctuation nn ee behavior as in the following equation[12, 24], PPss = rr02 |nn ee |2 λλ2ii LL2 PPii, where Ps is the scattered power, r0 is the classical electron radius, λi is the probing wave’s wavelength, L is the scattering length, and Pi is the probing wave power
We developed the invessel focusing antenna
Summary
Multi-scale turbulence interaction, especially, mixed micro-scale turbulence phenomena which includes both the ion and the electron scale turbulences, is of interest[1] in the high temperature plasma confinement study at present and there are many theoretical studies[2,3,4,5,6,7,8]. The electron density is higher than 1x1019m-3 in the usual LHD plasma experiments, the diagnostic region is almost in α >1. This means that the scattering signal is collective, and the scattering signal originates from correlated density fluctuation nn ee behavior as in the following equation[12, 24], PPss = rr02 |nn ee |2 λλ2ii LL2 PPii , where Ps is the scattered power, r0 is the classical electron radius, λi is the probing wave’s wavelength, L is the scattering length, and Pi is the probing wave power. We describe the in-vessel focusing antenna and the millimeter wave circuits of back-scattering system and its characteristics as follows
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