Comparison of 3D flux-driven scrape-off layer turbulence simulations with gas-puff imaging of Alcator C-Mod inner-wall limited discharges

Abstract

We carry out a quantitative comparison between gas-puff imaging (GPI) turbulence measurements in Alcator C-Mod inner-wall limited discharges (Zweben et al 2009 Phys. Plasmas 18 082505) and 3D ux-driven drift-reduced Braginskii turbulence simulations of scrape-off layer dynamics. The comparison is carried out for a series of inner-wall limited discharges where the magnetic eld and the density are varied. The comparison between GPI data and non-linear simulations yields overall good agreement for several observables, such as the D α emission levels and intermittency, the radial and poloidal correlation lengths and propagation velocities, and the power and frequency spectral density.

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

“…However, due to the difficulty of turbulence measurements and the complexity of nonlinear computational simulations, the quantitative connection between experiment and theory is still under investigation, e.g., Ref. 3.…”

“…A list of measurements which have been done using GPI is given in 3. GPI images from the Alcator C-Mod tokamak made at two different 6 cm × 6 cm regions using D 2 gas with the Balmer-α line filter.…”

“…3,62,104 However, since these turbulence codes are very complex and not yet "validated," they cannot be used to check the GPI data itself. There also seems to be no experimental configuration in which the GPI diagnostic can be "benchmarked" against known plasma fluctuations since even the simplest magnetized plasma instabilities are nonlinear and difficult to understand quantitatively.…”

Plasma turbulence in the scrape-off layer of the ISTTOK tokamak

“…A thorough comparison with experimental measurements was carried out with significant success. 15 The question of how these findings can be applied to other configurations remains open and is one of the main motivations of this work.…”

“…18 These are solved with GBS, 19,20 a numerical code developed with the goal of simulating plasma SOL turbulence by evolving the full profiles of the various plasma quantities with no separation between perturbations and equilibrium, and was validated against experiments such as the TORPEX device 21 and several other machines, 15 verified with the method of manufactured solutions, 22 and benchmarked against other major SOL simulation codes, including BOUTþþ, 23 HESEL, 24 and TOKAM3X. 8 The parameters of our study rely on the ones from ISTTOK, where a clear asymmetry between the low and the high field sides was found.…”