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Title: A phase contrast imaging–interferometer system for detection of multiscale electron density fluctuations on DIII-D

Abstract

Heterodyne interferometry and phase contrast imaging (PCI) are robust, mature techniques for measuring low-k and high-k electron density fluctuations, respectively. Here, we describe the first-ever implementation of a combined PCI-interferometer. The combined system uses a single 10:6 μm probe beam, two interference schemes, and two detectors to measure electron density uctuations at large spatiotemporal bandwidth (10 kHz < f < 5MHz and 0 cm -1 ≤ k ≤ 20 cm -1), allowing simultaneous measurement of ion- and electron-scale instabilities. Further, correlating our interferometer's measurements with those from DIII-D's pre-existing, toroidally separated interferometer allows core-localized, low-n MHD studies that may otherwise be inaccessible via external magnetic measurements. In the combined diagnostic's small port requirements and minimal access restrictions make it well-suited to the harsh neutron environments and limited port space expected in next-step devices.

Authors:
ORCiD logo [1]; ORCiD logo [1];  [1];  [1];  [2]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
  2. General Atomics, San Diego, CA (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1371887
Grant/Contract Number:
FC02-04ER54698; FG02-94ER54235; FC02-99ER54512
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 87; Journal Issue: 11; Related Information: E.M. Davis, J.C. Rost, M. Porkolab, A. Marinoni, and M.A. Van Zeeland, "A phase contrast imaging-interferometer system for detection of multiscale electron density fluctuations on DIII-D", Rev. Sci. Instr. 87, 11E117 (2016); Journal ID: ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Davis, E. M., Rost, J. C., Porkolab, M., Marinoni, A., and Van Zeeland, M. A.. A phase contrast imaging–interferometer system for detection of multiscale electron density fluctuations on DIII-D. United States: N. p., 2016. Web. doi:10.1063/1.4960727.
Davis, E. M., Rost, J. C., Porkolab, M., Marinoni, A., & Van Zeeland, M. A.. A phase contrast imaging–interferometer system for detection of multiscale electron density fluctuations on DIII-D. United States. doi:10.1063/1.4960727.
Davis, E. M., Rost, J. C., Porkolab, M., Marinoni, A., and Van Zeeland, M. A.. 2016. "A phase contrast imaging–interferometer system for detection of multiscale electron density fluctuations on DIII-D". United States. doi:10.1063/1.4960727. https://www.osti.gov/servlets/purl/1371887.
@article{osti_1371887,
title = {A phase contrast imaging–interferometer system for detection of multiscale electron density fluctuations on DIII-D},
author = {Davis, E. M. and Rost, J. C. and Porkolab, M. and Marinoni, A. and Van Zeeland, M. A.},
abstractNote = {Heterodyne interferometry and phase contrast imaging (PCI) are robust, mature techniques for measuring low-k and high-k electron density fluctuations, respectively. Here, we describe the first-ever implementation of a combined PCI-interferometer. The combined system uses a single 10:6 μm probe beam, two interference schemes, and two detectors to measure electron density uctuations at large spatiotemporal bandwidth (10 kHz < f < 5MHz and 0 cm-1 ≤ k ≤ 20 cm-1), allowing simultaneous measurement of ion- and electron-scale instabilities. Further, correlating our interferometer's measurements with those from DIII-D's pre-existing, toroidally separated interferometer allows core-localized, low-n MHD studies that may otherwise be inaccessible via external magnetic measurements. In the combined diagnostic's small port requirements and minimal access restrictions make it well-suited to the harsh neutron environments and limited port space expected in next-step devices.},
doi = {10.1063/1.4960727},
journal = {Review of Scientific Instruments},
number = 11,
volume = 87,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
Free Publicly Available Full Text
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  • Heterodyne interferometry and phase contrast imaging (PCI) are robust, mature techniques for measuring low-k and high-k electron density fluctuations, respectively. This work describes the first-ever implementation of a combined PCI–interferometer. The combined system uses a single 10.6 μm probe beam, two interference schemes, and two detectors to measure electron density fluctuations at large spatiotemporal bandwidth (10 kHz
  • A near-infrared laser phase contrast optical system incorporating a folded beam was developed in order to measure the distribution of density fluctuations in a high-temperature plasma. The coherent light source used was an yttrium aluminum garnet laser stabilized by a ring oscillator. The probe beam system separates and reflects the incident and exiting beams with a polarizer and a fully reflective mirror with a waveplate. This system was employed with a compact helical system to detect fluctuations at the plasma edge.
  • A novel rotating mask system has been designed and implemented on the DIII-D phase contrast imaging (PCI) diagnostic to produce the first spatially localized PCI measurements of a tokamak plasma. The localization technique makes use of the variation in the magnetic field component perpendicular to the viewing chord as a function of chord height. This new capability provides measurements in the range of 2<k<30 cm{sup -1}, 10 kHz<f<10 MHz, and 0.7<r/a<1. This technique provides a spatial resolution of 10 cm at k=15 cm{sup -1} and can realistically provide measurements at a rate of 10 profiles/s. Calibration measurements show accurate characterizationmore » of the system transfer function making feasible a time dependent analysis that results in improved localization. Initial measurements show turbulence to peak near the plasma edge. This upgrade is part of a broader program to operate the DIII-D PCI at wave numbers up to 40 cm{sup -1} to probe electron scale turbulence in the plasma core.« less
  • To more accurately suppress the phase fluctuation of the interference beams of a large-area phase-contrast X-ray imaging system using a two-crystal X-ray interferometer, a new feedback positioning system (FPS) has been developed and applied. The motion of interference patterns replaces the intensity of the interference beam in a small region as the feedback signal used in controlling the rotation of crystal blocks relative to each other. This FPS kept the phase fluctuation of the interference beams within {pi}/15 over more than six hours. Examples of high-quality two and three-dimensional images of biological samples obtained by the imaging system with themore » new FPS are given.« less
  • An imaging diagnostic for the observation of plasma density fluctuations is presented. It is based on the phase contrast method, and is used on the TCA tokamak to investigate fluctuations associated with plasma turbulence and driven waves in radio frequency heating experiments. The diagnostic uses a 23-cm-wide CO/sub 2/ laser beam transmitted through the plasma, and produces an image of the plasma where the small phase shifts (chemically bondphichemically bondapprox.10/sup -5/ to 10/sup -3/) due to refractive perturbations are revealed as corresponding intensity variations. A wide range of fluctuation wavelengths between 0.2 and about 20 cm is accessible to observation,more » with a sensitivity better than 10/sup -5/ rad for a 1-MHz bandwidth.« less