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Title: High spatial resolution upgrade of the electron cyclotron emission radiometer for the DIII-D tokamak

The 40-channel DIII-D electron cyclotron emission (ECE) radiometer provides measurements of T{sub e}(r,t) at the tokamak midplane from optically thick, second harmonic X-mode emission over a frequency range of 83–130 GHz. The frequency spacing of the radiometer's channels results in a spatial resolution of ∼1–3 cm, depending on local magnetic field and electron temperature. A new high resolution subsystem has been added to the DIII-D ECE radiometer to make sub-centimeter (0.6–0.8 cm) resolution T{sub e} measurements. The high resolution subsystem branches off from the regular channels’ IF bands and consists of a microwave switch to toggle between IF bands, a switched filter bank for frequency selectivity, an adjustable local oscillator and mixer for further frequency down-conversion, and a set of eight microwave filters in the 2–4 GHz range. Higher spatial resolution is achieved through the use of a narrower (200 MHz) filter bandwidth and closer spacing between the filters’ center frequencies (250 MHz). This configuration allows for full coverage of the 83–130 GHz frequency range in 2 GHz bands. Depending on the local magnetic field, this translates into a “zoomed-in” analysis of a ∼2–4 cm radial region. Expected uses of these channels include mapping the spatial dependence of Alfven eigenmodes,more » geodesic acoustic modes, and externally applied magnetic perturbations. Initial T{sub e} measurements, which demonstrate that the desired resolution is achieved, are presented.« less
Authors:
 [1] ;  [2]
  1. Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
  2. Institute for Fusion Studies, University of Texas, Austin, Texas, 78712 (United States)
Publication Date:
OSTI Identifier:
22308607
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 85; Journal Issue: 11; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; ALFVEN WAVES; DISTURBANCES; DOUBLET-3 DEVICE; EIGENFREQUENCY; ELECTRON CYCLOTRON-RESONANCE; ELECTRON EMISSION; ELECTRON TEMPERATURE; FREQUENCY MIXING; GEODESICS; GHZ RANGE; MAGNETIC FIELDS; MHZ RANGE; MICROWAVE RADIATION; OSCILLATION MODES; OSCILLATORS; RADIOMETERS; SPACE DEPENDENCE; SPATIAL RESOLUTION