Institute of plasma physics › Structure of IPP › Fusion Plasma Division › COMPASS › Diagnostics › Spectroscopic diagnostics
Thomson scattering diagnostics
Measured quantities: |
Electron temperature, electron density |
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Spatial resolution: |
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Temporal resolution: | 30 Hz with double probing energy 60 Hz two measurements with variable time gap (1 μs – 17 ms) running at 30 Hz |
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Responsible person: | |||||
Collaboration: |
Electron Kinetics Group, MAST Tokamak, Culham Centre for Fusion Energy, Abingdon, UK FOM-Institute for Plasma Physics Rijnhuizen, Nieuwegein, Netherlands Institute for Energy Research – Plasma Physics, Forschungszentrum Jülich GmbH, Germany Department of Control Engineering, Faculty of Electrical Engineering, Czech Technical University, Prague, Czech Republic |
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Thomson scattering is a laser-aided diagnostic widely used in the field of high-temperature plasma diagnostics
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Perform well localized measurements of the electron temperature and density in the plasma
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Scattering of monochromatic electromagnetic radiation from hot electrons in a plasma leads to a spectral broadening of the scattering spectrum due to the Doppler effect
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Electron temperature is determined from a spectral width of the Thomson scattered signal, electron density from scattered signal intensity

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Two Nd:YAG lasers (1064 nm): 1.5 J energy, 7 ns pulse duration, 30 Hz repetition rate each
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Two objectives for collecting the scattered light from both the core and the edge plasma regions. The light is then focused on bundles of optical fibres
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Optical fibres to transfer the scattered light to polychromators:
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12 bundles of fibres for core plasma region
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16 bundles of optical fibres to for the edge plasma region
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1 special bundle for alignment of the diagnostic
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Polychromators for spectral analysis of the scattered light
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28 polychromators analyzing the light from 56 spatial points in plasma (2 adjacent spatial points served by one polychromator) and 1 polychromator used for both alignment and the light spectral analysis
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Spectral analysis done by a set of five spectral filters specifically designed for the range of temperatures of 10 eV – 5 keV
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Detectors - Avalanche photodiodes possessing enhanced infrared sensitivity, developed specifically for the needs of this diagnostic
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Fast analog-digital converters (ADCs) for digitization of analog signals coming from detectors
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Signals (120 spectral channels) from polychromators are synchronously digitalized by fast and slow ADCs
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The fast ADCs convert data with high throughput of 1 GSample/sec and 8 bit resolution
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The slow digitizers: 16 bit ADC per channel with sampling rate of 500 kSample/sec
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Fig.1: Spatial profiles measured by Thomson scattering for shot No 6962. From the top: Electron temperature, electron pressure and electron density.