  The DTS experiment is a spherical Couette flow experiment with an imposed
dipolar magnetic field. Liquid sodium is used as a working fluid. In a series
of measurement campaigns, we have obtained data on the mean axisymmetric
velocity, the mean induced magnetic field and electric potentials. All these
quantities are coupled through the induction equation. In particular, a strong
omega-eff ect is produced by di fferential rotation within the fluid shell,
inducing a significant azimuthal magnetic field. Taking advantage of the simple
spherical geometry of the experiment, I expand the azimuthal and meridional
fields into Legendre polynomials and derive the expressions that relate all
measurements to the radial functions of the velocity field for each harmonic
degree. For small magnetic Reynolds numbers Rm the relations are linear, and
the azimuthal and meridional equations decouple. Selecting a set of
measurements for a given rotation frequency of the inner sphere (Rm = 9.4), I
invert simultaneously the velocity and the magnetic data and thus reconstruct
both the azimuthal and the meridional fields within the fluid shell. The
results demonstrate the good internal consistency of the measurements, and
indicate that turbulent non-axisymmetric fluctuations do not contribute
significantly to the axisymmetric magnetic induction.
