Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session CP18: Poster Session: Magnetic Confinement: Measurement & Diagnostic Techniques (2:00pm - 5:00pm)On Demand
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CP18.00001: 2-Dimensional, Second-Harmonic, Dispersion Interferometer for Plasma-Density Imaging Frank J Wessel, Fernando Brandi Conventional optical interferometers, used for plasma-density measurements, are typically robustly mounted, two-arm, high-cost installations. The Second-Harmonic Dispersion Interferometer (SHDI) is an exception, utilizing a common path, single-laser source frequency doubled before, and after, the sample, which allows the dispersive-phase shift of the SH beams to be measured in a simple, low-cost system. Present SHDI's provide a 1-D (line-of-sight) measurement, usually configured with a CW Nd:YAG, or CO$_2$ laser. We compared the performance of these SHDI's to that of a conventional $\mu$-wave interferometer, finding the Nd:YAG to be the most stable and least complex system design.$\footnote{F. Brandi, F.J.Wessel, C.Lohff, J.R.Duff, Z.O.Haralson, Expt. Study of SHDI's for Plasma Density Measurements, Applied Optics, to appear.}$ Recently, we upgraded the SHDI for 2-Dimensional, time-resolved imaging, using a pulsed Nd:YAG laser, beam-expansion optics, digital cameras, and image-processing s/w, providing: $>$10 mRad phase change, 100 $\mu$m resolution, 1 ns sampling time, and 100 Hz frame rate, in a 0.6-cm diameter beam,$\footnote{F.Brandi and F.J.Wessel, 2D-SHDI, Optics Letters, to appear.}$ suitable for a line-integrated plasma density, $\int n \cdot dl > 10^{14}$ cm$^{-2}$. [Preview Abstract] |
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CP18.00002: Error Analysis on Statistical Filament Data from Stereoscopic Fast Cameras on MAST Ryan Chaban, Tom Farley, Saskia Mordijck, Nick Walkden, Fulvio Militello, James Harrison, Andrew Kirk Fast camera images are tomographically inverted using a magnetic field line based technique to generate data on filamentary structures as they cross the separatrix and propagate through the SOL. This technique has been developed on MAST for a one-camera setup, and in a 2009 campaign stereoscopic cameras were mounted collecting synchronized data. We use this data to study the veracity of the diagnostic by comparing the statistical distributions derived from each camera separately and using both cameras' data with a shift optimization and correlation. The statistical distribution parameters for each camera agree for major and minor axis blob size. The parameters disagree for blob amplitude, however this is expected in the absence of absolute camera sensitivity calibrations. Lognormal fits to the blob radial displacement from separatrix show close agreement in the positions of their peaks, but inconsistencies in their shape parameters. The uniform distribution fit to the toroidal blob position is systematically shifted 5 cm suggesting the position of the camera affects the location sensitivity of the detections. This agrees with our optimization technique which shows a consistent shift between the cameras implying uncertainty in a single camera inversion of $+$/- 0.5 cm radially and $+$/- 5 cm toroidally. [Preview Abstract] |
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CP18.00003: Abstract Withdrawn
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CP18.00004: Refinement of the two-filter radiometric method for determining gross W erosion in the WEST tokamak D.C. Easley, A.L. Neff, C.C. Klepper, E.A. Unterberg, D.C. Donovan The validity of a low Ar intensity assumption in a two-filter radiometer with a W-I filter design is examined using experimental data collected during the 2018-2019 WEST campaigns. Accurate measurements of the gross W sputtering rate are essential to understanding the magnitude and location of scrape-off layer contamination due to PMI effects. Hence, a two-filter radiometric technique is used for cross-calibrating W line-emission spectroscopy throughout WEST. Here, a line filter from 399.9 to 401.2 nm was used to isolate the 400.9 nm W-I emission line. Moreover, a 401.45 nm Ar-II peak was known to lie just outside the bound of this main filter during the design and to have negligible parasitic contribution to the W-I signal because it was considered sufficiently attenuated by the main W-I filter. Recently however, it has been shown that the Ar-II peak can contribute to the W-I signal. Here, the validity of the assumptions used in this two-filter radiometric technique are reassessed by characterizing regimes of W/Ar line intensity ratios with standard spectroscopy. We also reassess the integration technique used for spectroscopic line fitting and compare this with the radiometric data of neighboring sightlines to validate the two-filter technique for any W/Ar ratio, providing a potential figure of merit for using the radiometers. [Preview Abstract] |
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CP18.00005: Zeeman Spectroscopic Determination of Magnetic Field in Gas-Puff Z-Pinches Jay Angel, Euan Freeman, Sander Lavine, Dave Hammer Zeeman Polarization Spectroscopy on 1 MA gas-puff z-pinches in Argon and Krypton is being used to determine the magnetic field distribution in the plasma during implosion. Light is collected parallel to the azimuthal magnetic field tangential to the gas puff implosion sheath. The light is split into left and right hand circularly polarized components and then focused into two linear fiber bundles and delivered to a 750 mm spectrometer. The Zeeman components can resolve the peaks of the two polarizations despite Stark Broadening. Introducing dopants into the gas puff will allow the use of additional emission lines, such as the Carbon IV doublet at 580.1 nm and 581.2 nm, to increase spatial resolution.~This method was developed for z-pinch experiments on a 500 kA, 500 ns rise time generator~by G. Rosenzweig, E. Kroupp, A. Fisher and Y. Maron, ``Measurements of the spatial magnetic field distribution in a z-pinch plasma throughout the stagnation process'' JINST 12, P09004 (2017) as part of the~Cornell/NNSA pulsed power center. [Preview Abstract] |
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