Diagnostic upgrades on the Maryland Centrifugal Experiment (MCX)

MCX studies supersonically rotating plasmas in a mirror-machine geometry. Theory predicts supersonic rotation in the azimuthal direction closes the loss cone and high velocity shear stabilizes MHD interchange modes. Construction began in September 2000 and the first rotating plasmas were formed in October 2002. The plasma is 2.6 m long between mirror throats and 28 cm outer radius, limited by the vacuum vessel. A longitudinal stainless steel electrode extends down the center of the machine, allowing a radial voltage of up to 10 kV to be applied by a 1.7 mF capacitor bank, recently upgraded to 7 mF. The magnetic mirrors can reach 19 kG and the midplane field can reach 3.1 kG, allowing mirror ratios up to 21. Diagnostics include Doppler spectroscopy, HeNe interferometry, dB/dt pickup coils, and diamagnetic loops. In addition, the current and voltage traces provide valuable diagnostic information. MCX has shown ion temperatures of ∼30 eV, rotation velocities of up to 80 km/s (for Mach numbers of 1-2) ion densities of 10 ²⁰ m ^-3 and near 100% ionization across a wide range of parameters. MCX plasmas are steady for several milliseconds, much longer than MHD instability times. We summarize MCX's design, recent upgrades, and results. Upgrades include expanding the capacitor bank to allow much longer shot times, implementation of diamagnetic loops and improved dB/dt coils, vacuum-UV spectroscopy, and time-resolved optical spectroscopy. Results include indicators of velocity profile, ion and neutral densities, confinement times, MHD stability, measurements of plasma pressure, a novel high speed rotation mode and mode transitions.