Plasma hole

Plasma hole has been observed in a magnetized cylindrical plasma. The measurements of ion flow velocity revealed that the plasma hole has a sink flow to the core on a plane perpendicular to the magnetic field and also an axial flow. The vorticity distribution determined by the flow velocity field shows localization near the center axis. According to the flow velocity field and the vorticity distribution, the plasma hole is identified as a Burgers vortex, which is intrinsic in viscous fluids and is observed in a plasma for the first time. The effective viscosity estimated from the characteristic scale length of vorticity localization exhibits an anomaly, which is three orders of magnitude higher than the classical value.