skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: 2D microwave imaging reflectometer electronics

Abstract

A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.

Authors:
; ; ; ; ;  [1];  [2]
  1. Electrical and Computer Engineering, University of California, Davis, California 95616 (United States)
  2. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
Publication Date:
OSTI Identifier:
22308621
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:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; APERTURES; CONTROL SYSTEMS; DENSITY; DOUBLET-3 DEVICE; ELECTRON DENSITY; ELECTRONIC EQUIPMENT; FLUCTUATIONS; MICROWAVE RADIATION; OPTICS; PLASMA; REFLECTION

Citation Formats

Spear, A. G., Domier, C. W., E-mail: cwdomier@ucdavis.edu, Hu, X., Muscatello, C. M., Ren, X., Luhmann, N. C., and Tobias, B. J. 2D microwave imaging reflectometer electronics. United States: N. p., 2014. Web. doi:10.1063/1.4891047.
Spear, A. G., Domier, C. W., E-mail: cwdomier@ucdavis.edu, Hu, X., Muscatello, C. M., Ren, X., Luhmann, N. C., & Tobias, B. J. 2D microwave imaging reflectometer electronics. United States. doi:10.1063/1.4891047.
Spear, A. G., Domier, C. W., E-mail: cwdomier@ucdavis.edu, Hu, X., Muscatello, C. M., Ren, X., Luhmann, N. C., and Tobias, B. J. Sat . "2D microwave imaging reflectometer electronics". United States. doi:10.1063/1.4891047.
@article{osti_22308621,
title = {2D microwave imaging reflectometer electronics},
author = {Spear, A. G. and Domier, C. W., E-mail: cwdomier@ucdavis.edu and Hu, X. and Muscatello, C. M. and Ren, X. and Luhmann, N. C. and Tobias, B. J.},
abstractNote = {A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.},
doi = {10.1063/1.4891047},
journal = {Review of Scientific Instruments},
number = 11,
volume = 85,
place = {United States},
year = {Sat Nov 15 00:00:00 EST 2014},
month = {Sat Nov 15 00:00:00 EST 2014}
}
  • Applicability of microwave imaging reflectometry (MIR) for the case of mirror device was numerically studied. The questions concerning radial localization of measurements, optimal position of optical system and imaging properties of MIR system were considered. The high curvature of the plasma cutoff layer and a relatively small distance from the plasma to the port are known to improve the performance of a conventional reflectometer. Nevertheless in the case of density fluctuations with wide wavenumber spectrum and large amplitude, the imaging reflectrometry shows better results than the conventional one.
  • A simple phase-sensitive microwave reflectometer is described which allows the complex reflection coefficient in a wave guide to be measured. The working principles, analysis of errors, and calibration experiments are described. (MOW)
  • A description of direct measurements of electron density in a positive column of glow discharge plasma in noble gases is presented. The measurements were performed in steady-state conditions, as well as in the presence of density oscillations. (MOW)
  • The edge density profile can play a significant role in determining the plasma confinement and the coupling of the ion cyclotron resonance frequency (ICRF) heating power to the plasma. To experimentally measure the edge density profile in the Tokamak Fusion Test Facility (TFTR), a two-frequency microwave reflectometer is being built. This reflectometer will operate in a swept two-frequency configuration between 91 and 118 GHz using the extraordinary mode. The frequency separation between the two microwave signals will be held constant while the signals are swept across the frequency band. By measuring the differential phase delay between these two signals, themore » density profile can be reconstructed. Two-frequency profile reflectometry is discussed and results of modeling of this type of reflectometer measurement for TFTR are shown. Finally, the design of the TFTR edge profile reflectometer microwave system is described.« less
  • A microwave reflectometer is in operation on TFTR for the measurement of density fluctuations. The system operates in the {ital X} mode and comprises three channels with fixed frequencies of 140, 132, and 125 GHz, and one with stepped frequency of 111--123 GHz. All channels use solid state Gunn oscillators and a heterodyne detection scheme. The system is located outside of the TFTR test cell with the power conveyed to the tokamak vessel by low-loss corrugated waveguides and remotely controlled parabolic mirrors. Preliminary results indicate that the level of density fluctuations with {ital k}{sub {perpendicular}} {lt}1 cm{sup {minus}1} is verymore » small in the central region of Ohmic plasmas ({ital {tilde n}}/{ital n}{lt}10{sup {minus}3}), and that it increases monotonically with minor radius to values of {approx}10{sup {minus}2} at {ital r}/{ital a}=0.9. This work supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.« less