Resolving the bulk ion region of millimeter-wave collective Thomson scattering spectra at ASDEX Upgrade

• Published in: Review of scientific instruments 2014-09, Vol.85 (9), p.093504-093504
• Main Authors: Stejner, M, Nielsen, S, Jacobsen, A S, Korsholm, S B, Leipold, F, Meo, F, Michelsen, P K, Moseev, D, Rasmussen, J, Salewski, M, Schubert, M, Stober, J, Wagner, D H
• Format: Article
• Language: English
• Subjects: ASDEX TOKAMAK; CALIBRATION; Digitization; FLUCTUATIONS; FOURIER ANALYSIS; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; ION TEMPERATURE; IONS; MHZ RANGE; Millimeter waves; PLASMA; Plasma composition; Populations; RESOLUTION; Rotating plasmas; Rotation; SAMPLING; Scientific apparatus & instruments; SIGNALS; SPECTRA; THOMSON SCATTERING; Upgrading; Variation; Velocity distribution
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.4894199

Collective Thomson scattering (CTS) measurements provide information about the composition and velocity distribution of confined ion populations in fusion plasmas. The bulk ion part of the CTS spectrum is dominated by scattering off fluctuations driven by the motion of thermalized ion populations. It thus contains information about the ion temperature, rotation velocity, and plasma composition. To resolve the bulk ion region and access this information, we installed a fast acquisition system capable of sampling rates up to 12.5 GS/s in the CTS system at ASDEX Upgrade. CTS spectra with frequency resolution in the range of 1 MHz are then obtained through direct digitization and Fourier analysis of the CTS signal. We here describe the design, calibration, and operation of the fast receiver system and give examples of measured bulk ion CTS spectra showing the effects of changing ion temperature, rotation velocity, and plasma composition.