Session CP18: Poster Session: Magnetic Confinement: Measurement & Diagnostic Techniques (2:00pm - 5:00pm)

2-Dimensional, Second-Harmonic, Dispersion Interferometer for Plasma-Density Imaging

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$^{-2}$.   

Abstract Withdrawn

An Advanced Research Projects Agency-Energy (ARPA-E) funded diagnostic system with high-portability has a planned deployment to the Princeton field-reversed configuration 2 (PFRC-2) device, located at Princeton Plasma Physics Laboratory. The diagnostic system, along with a team of researchers from Oak Ridge National Laboratory, will travel to PFRC-2 to measure important plasma parameters (n$_{\mathrm{e}}$, T$_{\mathrm{e}}$, n$_{\mathrm{i}}$, T$_{\mathrm{i}}$, v$_{\mathrm{i}})$ utilizing Thomson scattering (TS) and optical emission spectroscopy (OES). Electron temperature exceeding 100 eV and a line averaged electron density of 1x10$^{\mathrm{19}}$ m$^{\mathrm{-3\thinspace }}$have been previously observed in PFRC-2 by other techniques. Using the laser-aided Thomson scattering measurement, the ORNL diagnostic system will provide localized electron temperature and density. Design implementation of the portable system along with a sensitivity analysis of the diagnostics on the PFRC-2 device will be discussed.   

Refinement of the two-filter radiometric method for determining gross W erosion in the WEST tokamak

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.   

Zeeman Spectroscopic Determination of Magnetic Field in Gas-Puff Z-Pinches

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.