Liquid-to-solid phase transition near triple point at low temperature

When expanding into vacuum, cryogenic liquids sometimes produce solid ribbon-shaped structures, through a rapid liquid to solid phase transition (see photo). Such phenomena was initially studied by the CEA SBT in collaboration with the French Centre for spatial studies (CNES) on liquid propellants at cryogenic temperatures. Their results showed a complex phase transition physics involving the evaporation of the liquid into gas, and the simultaneous solidification of the liquid caused by a dramatic cooling of the environment due to evaporation. The production of such solid ribbons near the solid-liquid-gas triple point was observed under certain conditions, but the complex mechanisms involved are still unravelled and the phenomena cannot be controlled so far.

The aim of this project is to build up a model of the physical processes involved during the expansion of a liquid injected into vacuum, taking into account the complex phase change events and their interactions leading to the solidification of the liquid. A Multiphysics Finite Elements Modelling code is used, in which the different phase transitions and the evaporation/condensation processes are included.

Complementary experimental investigations are carried out in parallel on a cryostat specifically modified to produce solid ribbons under controlled conditions and with different materials (i.e. hydrogen, methane, argon). The results are used to validate the numerical predictions and refine the model.

Controlling the production of solid hydrogen ribbons at the micro scale is a complex challenge but would open very interesting applications: in the field of high power and high repetition rate LASERS for instance, micro targets made of pure material are impacted by the LASER which produces dense beams of ions (protons in the case of solid hydrogen targets). Such high energy protons are currently studied in cancer therapy for the treatment of malignant tumours. This field requires well calibrated, micro sized and pure solid materials that could be produced at high rate over long periods of time, to serve as targets for LASERS. The production of cryogenic hydrogen ribbons seems a promising way towards this goal.