Poloidal field measurements in the ST tokamak by harmonic generation at the upper hybrid layer

An extraordinary incident wave propagating along the major radius through the ST tokamak plasma is used to generate a second harmonic wave at the upper hybrid layer. Remote polarization measurements of the harmonic yield the poloidal magnetic field profile. The estimated over-all error in the measurement of the rotation angle of the total magnetic field is ≃0.3×10−2 rad. Further improvements in the accuracy of the measurements which are required to specify the current density profile unambiguously are discussed.