Data processing techniques for density profile evaluation from FM{endash}CW reflectometry

Journal Article · Wed Jan 01 04:00:00 EST 1997 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.1147767· OSTI ID:451913

Varela, P; Silva, A; Manso, M; Santos, J; Nunes, F ^[1]

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1. Associacao EURATOM/IST, Centro de Fusao Nuclear/Instituto Superior Tecnico, 1096 Lisboa Codex (Portugal)

Microwave reflectometry is an important diagnostic to measure the plasma density profile on present fusion experiments and on next devices like ITER. Several data processing techniques, currently employed to evaluate the density profile, use filtering algorithms to overcome the effect of plasma fluctuations. However, in these processes the detailed profile structure may be altered or even lost. In order to study this problem we applied two different data analysis methods to experimental results obtained in ASDEX, when a locked magnetohydrodynamic mode is present. The first method uses a software implementation of a frequency discriminator to estimate continuously the evolution of the group delay versus frequency and the second applies a sliding fast Fourier transform method to determine an averaged group delay curve. It is shown that the profile exhibits a density plateau due to the magnetic island, which can be lost due to filtering or averaging procedures. Next we perform a numerical study for a profile with a small rotating density plateau, disturbed by random noise to simulate the effect of plasma fluctuations. The frequency discriminator is used to obtain group delay sweeps from consecutive sweeps and a two-dimensional (2-D) regularization technique is applied to the multiple samples. It is shown that the 2-D method has advantages in the routine evaluation of the detailed profile structure masked under the effect of plasma turbulence, due to the combined averaging (over space and time), based on the correlation between neighboring data points. {copyright} {ital 1997 American Institute of Physics.}

• OSTI ID: 451913
• Report Number(s): CONF-960543--
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 1 Vol. 68; ISSN 0034-6748; ISSN RSINAK
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ASDEX TOKAMAK
DATA ANALYSIS
FLUCTUATIONS
FOURIER TRANSFORMATION
FREQUENCY MODULATION
MICROWAVE RADIATION
PLASMA DENSITY
PLASMA DIAGNOSTICS
REFLECTION
TOKAMAK DEVICES
fast Fourier transforms
microwave reflectometry
physics computing
plasma fluctuations