A multichannel, frequency-modulated, tunable Doppler backscattering and reflectometry system
- Department of Physics and Astronomy, University of California-Los Angeles, Los Angeles, California 90095-1547 (United States)
A novel multichannel Doppler backscattering system has been designed and tested for application on the DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] and National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] fusion plasma devices. Doppler backscattering measures localized intermediate wavenumber (k{sub perpendicular}{rho}{sub i}{approx}1-4,k{sub perpendicular}{approx}2-15 cm{sup -1}) density fluctuations and the propagation velocity of turbulent structures. Microwave radiation is launched at a frequency that approaches a cutoff layer in the plasma and at an angle that is oblique to the cutoff layer. Bragg backscattering occurs near the cutoff layer for fluctuations with k{sub perpendicular}{approx_equal}-2k{sub i}, where k{sub i} is the incident probe wave vector at the scattering location. The turbulence propagation velocity can be determined from the Doppler shift in the return signal together with knowledge of the scattering wavenumber. Ray tracing simulations are used to determine k{sub perpendicular} and the scattering location. Frequency modulation of a voltage-controlled solid state microwave source followed by frequency multiplication is used to create an array of finely spaced ({Delta}f=350 MHz) frequencies spanning 1.4 GHz. The center of the array bandwidth is tunable within the range of {approx}53-78 GHz. This article details the system design, laboratory tests, and presents initial data from DIII-D plasmas.
- OSTI ID:
- 22051021
- Journal Information:
- Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 8 Vol. 80; ISSN 0034-6748; ISSN RSINAK
- Country of Publication:
- United States
- Language:
- English
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