2020, Schuster, A.K., Hartley, N.J., Vorberger, J., Döppner, T., Van Driel, T., Falcone, R.W., Fletcher, L.B., Frydrych, S., Galtier, E., Gamboa, E.J., Gericke, D.O., Glenzer, S.H., Granados, E., MacDonald, M.J., MacKinnon, A.J., McBride, E.E., Nam, I., Neumayer, P., Pak, A., Prencipe, I., Voigt, K., Saunders, A.M., Sun, P., Kraus, D.

We present measurements of the nucleation rate into a diamond lattice in dynamically compressed polystyrene obtained in a pump-probe experiment using a high-energy laser system and in situ femtosecond x-ray diffraction. Different temperature-pressure conditions that occur in planetary interiors were probed. For a single shock reaching 70 GPa and 3000 K no diamond formation was observed, while with a double shock driving polystyrene to pressures around 150 GPa and temperatures around 5000 K nucleation rates between 1029 and 1034m-3 s-1 were recorded. These nucleation rates do not agree with predictions of the state-of-the-art theoretical models for carbon-hydrogen mixtures by many orders of magnitude. Our data suggest that there is significant diamond formation to be expected inside icy giant planets like Neptune and Uranus. © 2020 authors. Published by the American Physical Society.