First time-resolved electron density measurements in the C-2W advanced field-reversed configuration plasmas from long-path compact second-harmonic interferometer.

Characterization of the plasma structure and density is critical for the diagnosis and control of C-2W plasma equilibria. To this end, two compact, highly portable, turnkey second harmonic interferometers are used to make measurements with greater flexibility than available from other diagnostics, providing important information in areas otherwise inaccessible to more complicated systems. The systems are based on a fiber-coupled 1064 nm Nd:YAG laser and provide a sensitivity of a few 1018 m-2 with a time resolution of a few microseconds. System upgrades were made to allow for beam paths in excess of 5 m. Initial data from two system configurations are presented, showing plasma translation and merged equilibria.