Density measurements during long pulse discharges in CMFX*

First interferometric plasma density measurements during long pulse operation of the Centrifugal Mirror Fusion Experiment (CMFX) are presented. A single chord, 10.6 <!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>μm heterodyne MIR Michelson interferometer with digital phase demodulation is used for plasma discharges exceeding 200 ms. Interferometer measurements are compared to density inferences from two separate and independent diagnostics: the current crowbar and the diamagnetic loops, both of which were successfully verified in the Maryland Centrifugal Experiment (MCX). Measured densities of order 10¹⁸ – 10¹⁹ m^-3 demonstrate the ability to control maximum density, which is a crucial step towards fusion reactor scaling. Comparisons to theory and future plans, including upgrades to the interferometer, are also discussed.