Stanford Team Cancels gravity in Liquid Oxygen

Investigators at Stanford have demonstrated the first cancellation of gravity on a fluid near its liquid-gas critical point. PI John Lipa reports that gravity was cancelled on liquid oxygen at 154K and 50 bars pressure using a 0.5 Tesla superconducting magnet with a gradient coil. Residual forces were estimated to be less than 5% of gravity. This removal of gravity forces allowed measurements of the compressibility of the fluid, an important parameter of theoretical interest, to be extended to a temperature resolution of about two parts in a million, an order-of-magnitude better than in any other substance. This result represents the opening up of a new method for investigating liquid-gas critical points much more closely than was previously possible on the ground. With more careful tuning of the magnetic lift force, a temperature resolution of one part in ten million appears possible, comparable with that achievable in space experiments. Using higher-field magnets, it is also possible to study the critical points of a range of fluids including argon, carbon dioxide, hydrogen, and the helium isotopes. This technique would allow a broad range of improved tests of critical point theory.