Measurements of CECE/nT-phase spot size at ASDEX Upgrade*

Turbulence is known to be responsible for anomalous transport in tokamaks, reducing energy confinement times and limiting reactor performance. The correlation electron cyclotron emission (CECE) and n_e-T_e cross-phase diagnostics installed on the ASDEX Upgrade (AUG) tokamak measure broadband, long wavelength (k_θρ_s approximately <0.3) electron temperature and density fluctuations, yielding insight into turbulence-driven transport. The poloidal spot size, determined by focusing optics, is critical in determining the physical dimensions of the turbulence measured, with a smaller value of spot size yielding higher poloidal resolution in the measurement. To measure the spot size of the combined CECE/ n_e-T_e cross-phase diagnostic in use at AUG, an identical optical set up is constructed and tested at MIT. Here we present the details of the optical set up as well as the results of the tests to determine the spot size of these diagnostics. These measurements will enable a more accurate analysis of CECE and n_e-T_e cross-phase data and improve our understanding of turbulent fluctuations.