Measurements of rotation frequency, plasma potential, ion temperature, and density in a vacuum‐arc centrifuge are described. The vacuum‐arc centrifuge is a magnetized plasma column 1 m long, 5 cm in diameter, with ne ∼1014 cm-3, and Ti ∼3 eV. The source of this plasma column is a vacuum‐arc discharge between a negatively biased cathode and a grounded‐mesh anode 6 cm downstream of it. This source plasma region is at one end of a 2‐m‐long vacuum vessel. An externally applied axial magnetic field collimates the plasma, which streams through the anode mesh and induces rotation. Rigid–rotor frequencies ∼105 rad s-1 lead to radial centrifugal separation between isotopes. A piezoelectrically scanned Fabry–Perot interferometer is used to measure ion temperature and rotation frequency. Langmuir probes are also used to corroborate these rotation measurements, and to measure the plasma potential and ion‐density profiles. These measurements lead to scaling laws for the rotation. The scaling laws are compared with the predictions of a simple fluid model of such centrifuges.