  First results of a new spherical Couette experiment are presented. The liquid
metal flow in a spherical shell is exposed to a homogeneous axial magnetic
field. For a Reynolds number Re=1000, we study the effect of increasing
Hartmann number Ha. The resulting flow structures are inspected by ultrasound
Doppler velocimetry. With a weak applied magnetic field, we observe an
equatorially anti-symmetric jet instability with azimuthal wave number m=3. As
the magnetic field strength increases, this instability vanishes. When the
field is increased further, an equatorially symmetric return flow instability
arises. Our observations are shown to be in good agreement with linear
stability analysis and non-linear flow simulations.
