SANS measurements of the vortex lattice allow information such as the penetration depth, coherence length, and the superconducting gap structure of a superconductor to be extracted. Intrinsic vortex lattice arrangements in the high-Tc superconductor YBa2Cu3O7 (YBCO) have been established as a function of field up to 25 T. However, the temperature dependence of the vortex lattice form factor (related to the superfluid density) and the vortex lattice structure has not been measured at fields above 16 T. We propose to measure this at the highest available field.