Advanced techniques for microwave reflectometry

Journal Article · Sat Dec 31 04:00:00 EST 1994 · Plasma Physics Reports

OSTI ID:416192

Sanchez, J; Branas, B; Luna, E de la; Estrada, T ^[1]; Zhuravlev, V ^[1]; Hartfuss, H J; Hirsch, M; Geist, T ^[2]; Segovia, J; Oramas, J L ^[3]

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1. Asociacion Euratom-CIEMAT, Madrid (Spain)
2. Max-Planck Institut fuer Plasmaphysik, Garching (Germany)
3. Univ. Politecnica, Madrid (Spain)

Microwave reflectometry has been applied during the last years as a plasma diagnostic of increasing interest, mainly due to its simplicity, no need for large access ports and low radiation damage of exposed components. Those characteristics make reflectometry an attractive diagnostic for the next generation devices. Systems used either for density profile or density fluctuations have also shown great development, from the original single channel heterodyne to the multichannel homodyne receivers. In the present work we discuss three different advanced reflectometer systems developed by CIEMAT members in collaboration with different institutions. The first one is the broadband heterodyne reflectometer installed on W7AS for density fluctuations measurements. The decoupling of the phase and amplitude of the reflected beam allows for quantitative analysis of the fluctuations. Recent results showing the behavior of the density turbulence during the L-H transition on W7AS are shown. The second system shows how the effect of the turbulence can be used for density profile measurements by reflectometry in situations where the complicated geometry of the waveguides cannot avoid many parasitic reflections. Experiments from the TJ-I tokamak will be shown. Finally, a reflectometer system based on the Amplitude Modulation (AM) technique for density profile measurements is discussed and experimental results from the TJ-I tokamak are shown. The AM system offers the advantage of being almost insensitive to the effect of fluctuations. It is able to take a direct measurement of the time delay of the microwave pulse which propagates to the reflecting layer and is reflected back. In order to achieve fast reconstruction for real time monitoring of the density profile application of Neural Networks algorithms will be presented the method can reduce the computing times by about three orders of magnitude. 10 refs., 10 figs.

• OSTI ID: 416192
• Journal Information: Plasma Physics Reports, Journal Name: Plasma Physics Reports Journal Issue: 1 Vol. 20; ISSN PPHREM; ISSN 1063-780X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
EXPERIMENTAL DATA
HETERODYNE RECEIVERS
MEASURING METHODS
NEURAL NETWORKS
PLASMA DENSITY
PLASMA DIAGNOSTICS
TJ-1 TOKAMAK
WENDELSTEIN-7 STELLARATOR