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Evaluation of a new DIII-D Doppler backscattering system for higher wavenumber measurement and signal enhancement

Journal Article · · Review of Scientific Instruments
DOI:https://doi.org/10.1063/5.0101864· OSTI ID:1961395
 [1];  [2];  [3];  [2];  [2];  [4];  [2]
  1. Univ. of California, Los Angeles, CA (United States); General Atomics, DIII-D National Fusion Facility
  2. Univ. of California, Los Angeles, CA (United States)
  3. Inst. of High Performance Computing (Singapore)
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
+ Show Author Affiliations
The high density fluctuation poloidal wavenumber, kθ (kθ > 8 cm–1, kθρs > 5, ρs is the ion gyro radius using the ion sound velocity), measurement capability of a new Doppler backscattering (DBS) system at the DIII-D tokamak has been experimentally evaluated. In DBS, wavenumber (k) matching becomes more important at higher wavenumbers, owing to the exponential dependence of the measured signal loss factor on wave vector mismatch. Wave vector matching allows for the Bragg scattering condition to be satisfied, which minimizes the signal loss at higher k’s. In the previous DBS system, without toroidal wave vector matching, the measured DBS signal-to-noise ratio at higher kθ (>8 cm–1) is substantially reduced, making it difficult to measure higher kθ turbulence. The new DBS system has been optimized to access higher wavenumber, kθ ≤ 20 cm–1, density turbulence measurement. The optimization hardware addresses fluctuation wave vector matching using toroidal steering of the launch mirror to produce a backscattered signal with improved intensity. The probe’s sensitivity to high-k density fluctuations has been increased by approximately an order of magnitude compared to the old system that has been in use at DIII-D. Note that typical measurement locations are above or below the tokamak midplane on the low field side with normalized radial ranges of 0.5–1.0. As a result, the new DBS probe system with the toroidal matching of fluctuation wave vectors is thought to be critical to understanding high-k turbulent transport in fusion-relevant research at DIII-D.
Research Organization:
General Atomics, San Diego, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Grant/Contract Number:
FC02-04ER54698; SC0019352
OSTI ID:
1961395
Alternate ID(s):
OSTI ID: 1895532
Journal Information:
Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 10 Vol. 93; ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English

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Figures / Tables (7)

FIG. 1(p. 2)figure FIG. 1
FIG. 2(p. 2)figure FIG. 2
FIG. 3(p. 3)figure FIG. 3
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FIG. 5(p. 4)figure FIG. 5
FIG. 6(p. 4)figure FIG. 6
FIG. 7(p. 5)figure FIG. 7

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY
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