Time-lapse Microtomography to access the 3D Growth of Snowflakes

The controlled growth of atmospheric snow crystals presently resists the in situ tomographic approach due to several reasons: 1) the difficult temperature and humidity regulation, 2) the rapid phenomena involved, 3) the tiny structure of some crystals, and 4) the practical need of pre-selecting a unique crystal among several growing seeds. These 4 items are major obstacles to access the evolution of such structures in 3D. We found solutions to most of these difficulties and could recently obtain a short series of crystal growth using our cold cell CellDyM3 on BM18 beamline. Based on this preliminary result, we propose to grow at least 2 very distinct types of crystals using CellDyM3 and to monitor their growth using time-lapse tomography. Such an experiment would allow to access a lot of geometrical parameters that cannot be commonly accessed with 2D optical measurements, and to provide reference growth evolutions for the evaluation of 3D ice crystal growth models.

当前，受控大气雪晶的生长研究难以通过原位断层扫描（in situ tomographic）技术开展，主要存在以下四项阻碍：1）温湿度调控难度极大；2）雪晶生长过程发生速率极快；3）部分雪晶的结构尺寸极其微小；4）实际实验中需从多个正在生长的晶种中预先筛选出单一目标晶种。上述四大难点均为获取此类结构三维演化信息的主要障碍。我们已攻克其中多数难题，近期依托BM18光束线的CellDyM3低温舱完成了一系列短时长的雪晶生长观测实验。基于此次初步实验结果，我们计划利用CellDyM3低温舱培育至少两种差异显著的雪晶，并通过延时断层扫描（time-lapse tomography）技术实时监测其生长过程。此类实验将可获取大量二维光学测量手段难以获取的几何参数，并可为三维冰晶生长模型的评估提供可靠的生长演化参考数据。