ECEI characterization of pedestal fluctuations in quiescent H-mode plasmas in DIII-D

Abstract

Electron cyclotron emission imaging (ECEI) is employed to characterize the magneto hydraulics dynamics (MHD) fluctuations at the quiescent H-mode pedestals in DIII-D. Pedestal MHD fluctuations cause ECE radiation temperature fluctuations δ T e ,rad in both the pedestal and scrape-off-layer (SOL). A synthetic ECE platform is utilized for detailed interpretation of the ECEI signals in the SOL and pedestal regions. It is observed that the ECE radiation δ T e ,rad , which is located in the SOL region according to the cold and optically thick plasma resonance assumption, is extremely sensitive to MHD radial displacements near the separatrix, exhibiting radiation inversion to δ T e ,rad at the pedestal. Here, the radiation inversion refers to the opposite phase between the radiation fluctuation at the pedestal and the radiation fluctuation at the SOL. Consequently, the quasi-coherent MHD (QCM), which displays a radiation inversion, is found to be consistent with an MHD radial structure that has a strong displacement near the separatrix. In contrast, the edge harmonic oscillation (EHO), which displays weak or no inversion, is found to be consistent with an MHD radial displacement structure peaking at the pedestal top. The ECEI data, interpreted with synthetic ECE, are in qualitative agreement with beam emission spectroscopy measurements on DIII-D for the relative radial extent and localization of the EHO and QCM. The high sensitivity of ECE radiation to separatrix displacements can be used to detect turbulence or MHD fluctuations near the separatrix, which may affect the transport across the separatrix and the wetted area in the divertor. The δ T e ,rad inversion measured with an ECE or ECEI system potentially provides important information on the magnetic field B sep at the separatrix, which helps constrain the pedestal equilibrium reconstruction and achieve an unambiguous mapping of the ECE/ECEI system with respect to the separatrix.

A synthetic diagnostics platform for microwave imaging diagnostics in tokamaks

“…This makes the electron temperature measured by ECEI appear higher than its actual value [2]. The signal intensity received by antenna at the electron cyclotron frequency and its harmonics is [9,[18][19][20][21]:…”

Benchmark of a self-consistent dynamic 1D divertor model DIV1D using the 2D SOLPS-ITER code

“…The roll-over is often explained by a power or recombination particle sink [25] such that an overestimated ionization source can skew the particle balance. This might be overcome by the addition of molecular recombination losses in the particle balance as molecular recombination rates are relevant at higher temperatures overtaking the ionization source at higher temperatures, initiating the roll-over at lower upstream densities [25,[27][28][29].…”