Maintenance mechanism of a circular surface wave in a magnetohydrodynamic cell and limits of its existence

A circular surface wave (CSW) of a low-temperature gallium alloy in the immovable cell with a central bottom electrode and an upper ring electrode exposed to axial magnetic fields is studied experimentally. The mechanism which provides the existence of a stable CSW is suggested. It is determined that, depending on the force parameter and geometrical characteristics of the cell, three modes can occur in the cell: rest, CSW, or axial rotation with a deep funnel on the surface providing the circular contact of the liquid metal with the electrode. A mode map showing the boundaries of the CSW existence domain is plotted on the parameter plane.