The interaction between strong THz radiation from a free electron laser and an electron sheet in a high-mobility, low-density, GaAs/AlGaAs structure has been investigated in magnetotransport experiments over a wide range of wavelengths, intensities, magnetic fields, and temperatures. Photovoltage and photocurrent effects are evident in both longitudinal and transverse potential differences. Broad cyclotron resonance is observed to high temperature and connected with a decrease in electron density. The change in electron temperature under THz radiation is estimated from changes in the magnitude of the magnetoresistivity oscillations at low lattice temperature. The effect of the magnetic field is to suppress the rise in electron temperature relative to the zero field case.