Imaging-based measurements of plasma turbulence in a linear device*

We present the status of our ongoing study of imaging-based plasma turbulence measurements in the Controlled Shear Decorrelation Experiment (CSDX) at the University of California, San Diego. CSDX is a well-characterized linear machine producing dense plasmas relevant to the tokamak edge ($T_e \sim 3$ eV, $n_e \sim 10^{13}$/cc). Electrostatic fluctuations are measured with Langmuir probe arrays in concert with fast imaging over a range of plasma parameters. Drift-wave-like modes are observed with frequencies of $3-30$ kHz ($\omega L_n/c_s \sim 0.2-2$) and wavenumbers of $0.3-6$ cm$^{-1}$ ($k\rho_s \sim 0.1-10$). Time-resolved velocity fields are obtained through pattern-matching velocimetry, allowing access to flow/turbulence interaction dynamics across the plasma radius. Current work includes measurements of mode structure, velocity profiles, Reynolds stress profiles, and ion-neutral coupling.