Spectroscopic measurements of plasma rotation and ion and neutral atom temperatures in the Maryland Centrifugal Experiment

In initial spectroscopic measurements on the Maryland Centrifugal Experiment, rotation velocities and directions for C+, C2+, C3+, and N+ ions and neutral hydrogen atoms have been obtained from the Doppler shifts of visible spectral lines. Ion and neutral temperatures have also been determined from Doppler broadening. Different rotation velocities and temperatures are observed for different species indicating that the inner plasma is hotter and rotates more rapidly than that at the edge. The direction of rotation is found to be consistent with the predicted Er¯×Bz¯ direction; and it reverses with the direction of the magnetic field. The magnitudes of the rotation velocities were of the same order as estimated from the applied voltage and magnetic field. For the C+, C2+, and C3+ species, rotation velocities of 20–30 km/s, 40–70 km/s, and 60–100 km/s are observed, respectively. The corresponding temperatures are 10–12 eV, 20–40 eV, and 25–40 eV. Neutral hydrogen atoms are observed to rotate with velocities ∼10 km/sec and with temperatures ∼5–10 eV. A figure of merit for centrifugal confinement is the thermal Mach number, M=(vφ/vthi), where vthi is the ion thermal speed. The observed ion velocities and temperatures correspond to M ranging from 1 to 2. Variations of rotation velocities and temperatures with axial magnetic field, radial electric field, and mirror ratio are described. An electron temperature of ≈15 eV is inferred from the relative line intensities from different ionic species of carbon, which is consistent with the lack of observable C4+ emission.