Direct comparison of GEMR edge turbulence simulations with Alcator C-Mod SOL turbulence measurements

We report a direct comparison of measured SOL turbulence in Alcator C-Mod plasmas to a computational model. The turbulence measurements were made with gas puff imaging (GPI) and Langmuir probes, and the simulations were performed by the GEMR gyrofluid electromagnetic code [Phys. Plasmas 12 (2005) 102307]. Plasma conditions were chosen the match the capabilities of the computational model: near-circular, Ohmic, inner wall limited, with B=2.9-5.4 T and Ip=0.4-0.8 MA at fixed q(a). The measured radial and poloidal correlation lengths in the C-Mod SOL were approximately a factor 1.5-2 larger than those predicted by GEMR, and both measured and computed correlation lengths showed a slow decrease with B, with relatively little change with SOL density. The measured and simulated autocorrelation times and frequency spectra were very similar at low B, but the measured autocorrelation time increased with B more strongly than in the simulations. Additional comparisons and limitations of these comparisons will be described.