Plasma rotation and axial flow velocities in Magnum-PSI from cross-correlation measurements

The plasma flow velocity in the azimuthal and axial directions was estimated from a cross-correlation analysis of ion saturation currents measured across the plasma column of Magnum-PSI using a 64-probe matrix acting as target. The radial profile of the plasma rotation velocity in azimuthal direction revealed a reversed rotation at larger radii (r > 12-16 mm, depending on the magnetic field strength). The result was confirmed by comparison with the azimuthal velocity calculated as the sum of the E×B drift (estimated from the radial profile of the plasma potential) and the diamagnetic drift (estimated from the radial profile of the ion pressure). The reversed rotation was associated with the electron current path in Magnum-PSI. The axial velocity was estimated based on the rotation velocity and cross-correlation measurements with a tilted target. Both the azimuthal and axial velocities are of the order of km s−1, corresponding to previously reported results obtained by optical methods.