2D Doppler backscattering using synthetic aperture microwave imaging of MAST edge plasmas

Abstract Doppler backscattering (DBS) is already established as a powerful diagnostic; its extension to 2D enables imaging of turbulence characteristics from an extended region of the cut-off surface. The Synthetic Aperture Microwave Imaging (SAMI) diagnostic has conducted proof-of-principle 2D DBS...

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Bibliographic Details
Published in:Nuclear Fusion
Main Authors: Thomas, D.A., Brunner, K.J., Freethy, S.J., Huang, B.K., Shevchenko, V.F., Vann, R.G.L.
Other Authors: Euratom research and training programme, Engineering and Physical Sciences Research Council, Research Councils UK
Format: Article in Journal/Newspaper
Language:unknown
Published: IOP Publishing 2016
Subjects:
sami
Online Access:http://dx.doi.org/10.1088/0029-5515/56/2/026013
http://stacks.iop.org/0029-5515/56/i=2/a=026013/pdf
http://stacks.iop.org/0029-5515/56/i=2/a=026013?key=crossref.bf20f9fa0cbba8ecdaf8d1f7ebcd8caf
https://iopscience.iop.org/article/10.1088/0029-5515/56/2/026013
https://iopscience.iop.org/article/10.1088/0029-5515/56/2/026013/pdf
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Summary:Abstract Doppler backscattering (DBS) is already established as a powerful diagnostic; its extension to 2D enables imaging of turbulence characteristics from an extended region of the cut-off surface. The Synthetic Aperture Microwave Imaging (SAMI) diagnostic has conducted proof-of-principle 2D DBS experiments of MAST edge plasma. SAMI actively probes the plasma edge using a wide (±40° vertical and horizontal) and tuneable (10–34.5 GHz) beam. The Doppler backscattered signal is digitised in vector form using an array of eight Vivaldi PCB antennas. This allows the receiving array to be focused in any direction within the field of view simultaneously to an angular range of 6–24° FWHM at 10–34.5 GHz. This capability is unique to SAMI and is a novel way of conducting DBS experiments. In this paper the feasibility of conducting 2D DBS experiments is explored. Initial observations of phenomena previously measured by conventional DBS experiments are presented; such as momentum injection from neutral beams and an abrupt change in power and turbulence velocity coinciding with the onset of H-mode. In addition, being able to carry out 2D DBS imaging allows a measurement of magnetic pitch angle to be made; preliminary results are presented. Capabilities gained through steering a beam using a phased array and the limitations of this technique are discussed.

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