Portable diagnostic package for Thomson scattering and optical emission spectroscopy on Princeton field-reversed configuration 2 (PFRC 2)

Journal Article · Thu Nov 03 00:00:00 EDT 2022 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/5.0101849· OSTI ID:1996250

Kafle, Nischal  ^[1]; Elliott, Drew  ^[1]; Berlinger, B. ^[2]; He, Zichen  ^[3]; Cohen, Samuel A.  ^[2]; Zhang, Zhili  ^[3]; Biewer, Theodore M.  ^[1]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
2. Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
3. Univ. of Tennessee, Knoxville, TN (United States)

An Advanced Research Projects Agency-Energy funded diagnostic system has been deployed to the Princeton field-reversed configuration 2 (PFRC-2) device, located at Princeton Plasma Physics Laboratory. The Portable Diagnostic Package (PDP), designed at Oak Ridge National Laboratory, allows for the measurement of Thomson Scattering (TS) for electron density and temperature and Optical Emission Spectroscopy (OES) for ion temperature, impurity density, and ion velocity. A tunable spectrometer on the PDP with three gratings provides the flexibility to measure low (1 eV) and high (1000 eV) electron temperature ranges from TS. Additionally, using a second spectrometer, the OES diagnostic can survey light emission from various ion excitation levels for wide wavelength ranges. The electron density (<2 × 10¹⁹ m^–3) of plasmas generated in PFRC-2 has been below the PDP TS discrimination threshold, which has made TS signal detection challenging against a high-background of laser stray light. The laser stray light was iteratively reduced by making modifications to the entrance and exit geometry on PFRC-2. Rayleigh scattering experiments on PFRC have yielded the TS discrimination sensitivity to be >1 × 10²⁰ m^–3 for the PDP. A recently implemented narrow-band notch spectral filter that masks the second harmonic 532 nm Nd:YAG laser wavelength has increased the system’s TS light discrimination sensitivity 65 times compared to the instance when the notch filter was not implemented. The hardware implementation including design changes to the flight tubes and Brewster windows will be discussed, along with results from Rayleigh and rotational Raman scattering sensitivity analyses, which were used to establish a quantitative figure of merit on the system performance. Further, the Raman scattering calibration with the notch filter has improved the PDP electron density threshold to 1 ± 0.5 × 10¹⁸ m^–3.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Advanced Research Projects Agency - Energy (ARPA-E)
• Grant/Contract Number: AC05-00OR22725; AC02-09CH11466; D.E.-AC05-00OR22725
• OSTI ID: 1996250
• Alternate ID(s): OSTI ID: 1896845
• Journal Information: Review of Scientific Instruments, Vol. 93, Issue 11; ISSN 0034-6748
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

47 OTHER INSTRUMENTATION
Raman scattering
Thomson scattering
optical emission spectroscopy
spectral discrimination
lasers
plasma discharges
plasma diagnostics