Validation of 2D T e and n e measurements made with helium imaging spectroscopy in the volume of the TCV divertor

Abstract Multi-spectral imaging of helium atomic emission (HeMSI) has been used to create 2D poloidal maps of T e and n e in TCV’s divertor. To achieve these measurements, TCV’s MANTIS multispectral cameras simultaneously imaged four He I lines (2 singlet and 2 triplet) and a He II line (468nm) from...

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Published in:Nuclear fusion 2023-03
Main Authors: Linehan, Bryan Lee, Perek, Artur, Duval, Basil P., Bagnato, Filippo, Blanchard, Patrick, Colandrea, Claudia, de Oliveira, Hugo, Février, Olivier, Flom, Erik, Gorno, Sophie, Goto, Motoshi, Marmar, Earl S., Martinelli, Lorenzo, Mathews, Abhilash, Munoz Burgos, Jorge Manuel, Mykytchuk, Dmytry, Offeddu, Nicola, Sales de Oliveira, Diego, Reimerdes, Holger, Reiter, Detlev, Schmitz, Oliver, Terry, Jim L., Theiler, Christian, Tsui, Cedric Kar-Wai, Vincent, Benjamin, Wijkamp, Tijs, Wüthrich, Curdin Tobias, Zholobenko, Wladimir
Format: Article
Language:English
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Summary:Abstract Multi-spectral imaging of helium atomic emission (HeMSI) has been used to create 2D poloidal maps of T e and n e in TCV’s divertor. To achieve these measurements, TCV’s MANTIS multispectral cameras simultaneously imaged four He I lines (2 singlet and 2 triplet) and a He II line (468nm) from passively present He and He + . The images, which were absolutely calibrated and covered the whole divertor region, were inverted through the assumption of toroidal symmetry to create emissivity profiles and, consequently, line-ratio profiles. A collisional-radiative model (CRM) was applied to the line-ratio profiles to produce 2D poloidal maps of T e and n e . The collisional-radiative modeling was accomplished with the Goto helium CRM code which accounts for electron-impact excitation and deexcitation (EIE), and electron-ion recombination (EIR) with He + . The HeMSI T e and n e measurements were compared with co-local Thomson scattering measurements. The two sets of measurements exhibited good agreement for ionizing plasmas: (5 eV ≤ Te ≤ 60 eV, and 2 × 10 18 m -3 ≤ ne ≤ 3 × 10 19 m -3 ) in the case of majority helium plasmas, and (10 eV ≤ Te ≤ 40 eV, 2 × 10 18 m -3 ≤ ne ≤ 3 × 10 19 m -3 ) in the case of majority deuterium plasmas. However, there were instances where HeMSI measurements diverged from Thomson scattering. When T e ≤ 10 eV in majority deuterium plasmas, HeMSI deduced inaccurately high values of T e . This disagreement cannot be rectified within the CRM’s EIE and EIR framework. Second, on sporadic occasions within the private flux region, HeMSI produced erroneously high measurements of n e . Multi-spectral imaging of Helium emission has been demonstrated to produce accurate 2D poloidal maps of T e and n e within the divertor of a tokamak for plasma conditions relevant to contemporary divertor studies.
ISSN:0029-5515
1741-4326
DOI:10.1088/1741-4326/acb5b0