We propose a study of the magnetic structure of isotopically enriched Gd2Ti2O7. We have successfully grown and characterised large single crystals using low-absorption 160Gd. In tandem with studies of the zero-field structure on D10 (submitted), and a neutron polarization analysis study of the zero-field diffuse scattering (D7, accepted) we here propose to follow the evolution of the magnetic structure in a magnetic field. Previous work indicates at least 3 distinct magnetic phases below a field of 8T, with highly anisotropic field dependence. We will seek to characterise all 3 low temperature phases, as well as look at the diffuse scattering due to the disordered Gd moments as a function of field. We will need 5 days on WISH to complete these measurements.