Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

Abstract

Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on the Alcator C-Mod tokamak [M. Greenwald, et al., Phys. Plasmas 21, 110501 (2014)]. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scattering and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment and with a Fourier space diagnostic designed to measure poloidal phase velocity. Blob velocities in the simulations were determined from the correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations, it was found that larger blobs moved poloidally with the ExB flow velocity, v E , in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, v E + 1/2 v di , where v di is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity for the discharge. The saturation mechanisms operative in the simulation of the discharge are also discussed. It is found that neither sheared flow nor pressure gradient modification can be excluded as saturation mechanisms. †email: dave@lodestar.com 2

Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

“…The measured widths are the same (within radial resolution), 107 but the absolute radial location of the mode differs by ∼5 mm. 107,117 The absolute location determination depends on the EFIT equilibrium reconstruction to map the measurements to a common radial grid, but the difference is somewhat outside of the estimated EFIT and registration uncertainties. The reasons for the differences are thus still under investigation.…”

Non-trace full-F gyro-fluid interchange impurity advection

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“…2016), SOLT (Russel et al. 2016) or GRILLIX (Ross et al. 2019), and the importance of FLR effects has been demonstrated with a delta-F gyro-fluid model (Madsen et al.…”

Deep modelling of plasma and neutral fluctuations from gas puff turbulence imaging

“…While the measurement regions spatially spanned by the two independent diagnostics are magnetically disconnected, we map the fluctuations to common poloidal magnetic flux coordinates based upon magnetohydrodynamic equilibrium reconstruction in the tokamak plasma using the EFIT code [52]. Deconstructing the GPI fluctuations into the turbulent n e , T e , and n 0 instead of the raw brightness from atomic emission largely resolves diagnostic misalignment challenges [53] and, in contrast with past analysis of plasma discharge 1120711021 [54], there is no radial shift applied to align the turbulent fluctuation profiles from these two independent experimental diagnostics. Profiles on these open field lines fluctuate strongly with perturbations of up to 10 -100%.…”