A novel Doppler backscattering (DBS) system to simultaneously measure radio frequency plasma fluctuations and low frequency turbulence

Chowdhury, Satyajit; Crocker, Neal A.; Peebles, W. A.; Rhodes, Terry L.; Zeng, Lei; Lantsov, R.; Van Compernolle, B.; Brookman, Michael; Pinsker, Robert I.; Lau, Cornwall

doi:10.1063/5.0149654

Title: A novel Doppler backscattering (DBS) system to simultaneously measure radio frequency plasma fluctuations and low frequency turbulence

Journal Article · 26 July 2023 · Review of Scientific Instruments

DOI: https://doi.org/10.1063/5.0149654 · OSTI ID:1993278

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Univ. of California, Los Angeles, CA (United States)
General Atomics, San Diego, CA (United States)
General Atomics, San Diego, CA (United States); Commonwealth Fusion Systems, Devens, MA (United States)
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

A novel quadrature Doppler Backscattering (DBS) system has been developed and optimized for the E-band (60–90 GHz) frequency range using either O-mode or X-mode polarization in DIII-D plasmas. In general, DBS measures the amplitude of density fluctuations and their velocity in the lab frame. The system can simultaneously monitor both low-frequency turbulence (f < 10 MHz) and radiofrequency plasma density fluctuations over a selectable frequency range (20–500 MHz). Detection of high-frequency fluctuations has been demonstrated for low harmonics of the ion cyclotron frequency (e.g., 2f_ci ~ 23 MHz) and externally driven high-frequency helicon waves (f = 476 MHz) using an adjustable frequency down conversion system. Importantly, this extends the application of DBS to a high-frequency spectral domain while maintaining important turbulence and flow measurement capabilities. This unique system has low phase noise, good temporal resolution (sub-millisecond), and excellent wavenumber coverage (k_θ ~ 1–20 cm^–1 and kr ≲ 30 cm^–1). As a demonstration, localized internal DIII-D plasma measurements are presented from turbulence (f ≤ 5 MHz), Alfvenic waves (f ~ 6.5 MHz), ion cyclotron waves (f ≥ 20 MHz), as well as fluctuations around 476 MHz driven by an external high-power 476 MHz helicon wave antenna. In the future, helicon measurements will be used to validate GENRAY and AORSA modeling tools for prediction of helicon wave propagation, absorption, and current drive location for the newly installed helicon current drive system on DIII-D.

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Research Organization:: Univ. of California, Los Angeles, CA (United States); General Atomics, San Diego, CA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)

Grant/Contract Number:: SC0020649; FC02-04ER54698; SC0020337

OSTI ID:: 1993278

Alternate ID(s):: OSTI ID: 1993078

Journal Information:: Review of Scientific Instruments, Vol. 94, Issue 7; ISSN 0034-6748

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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