Diagnosing the pedestal magnetic field and magnetohydrodynamics radial structure with pedestal–scrape of layer electron cyclotron emission radiation inversion in H-mode plasma (invited)

• Published in: Review of scientific instruments 2022-10, Vol.93 (10)
• Main Authors: Yu, Guanying, Zhu, Yilun, Austin, Max, Chen, Ying, Cao, J., Diallo, A., Kramer, G. J., Li, Zeyu, Li, X., Liu, Xianzi, Nazikian, Raffi, Zheng, Yuan, Luhmann, Jr., N. C.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; magnetic fields; Maxwell-Boltzmann distribution; optical properties; plasma confinement; plasma instabilities; spectrograms; tokamaks; transport properties
• ISSN: 0034-6748; 1089-7623

Forward modeling is used to interpret inversion patterns of the pedestal–Scrape of Layer (SOL) Electron Cyclotron Emission (ECE) in DIII-D H-mode experiments. The modeling not only significantly improves the ECE data interpretation quality but also leads to the potential measurements of (1) the magnetic field strength |B| at the separatrix, (2) the pedestal |B| evolution during an inter-Edge Localized Mode (ELM) period, and (3) the pedestal Magnetohydrodynamics (MHD) radial structure. The ECE shine-through effect leads to three types of pedestal–SOL radiation inversions that are discussed in this paper. The first type of inversion is the non-monotonic Te,rad profile with respect to the major radius. Using the ECE frequency at the minimum Te,rad, the inversion can be applied to measure the magnetic field |B| at the separatrix and calibrate the mapping of the ECE channels with respect to the separatrix. The second type of inversion refers to the opposite phase between the radiation fluctuations δTe,rad at the pedestal and SOL. This δTe,rad phase inversion is sensitive to density and temperature fluctuations at the pedestal foot and, thus, can be used to qualitatively measure the MHD radial structure. The third type of inversion appears when the pedestal and SOL Te,rad evolve in an opposite trend, which can be used to infer the pedestal |B| field change during an inter-ELM period. Finally, the bandwidth effect on measuring δTe,rad due to pedestal MHD is also investigated in the radiation modeling.