Early Planet Formation: A Facility to Study the Time Evolution and Equilibrium States of Multitudes of Interacting sub-millimeter to centimeter Dust and Ice Aggregate Ensembles

行星的形成发生在新形成恒星周围的吸积盘（原行星盘）中。早期阶段主要是尘埃和冰聚集体的碰撞生长：最初微米大小的尘埃和冰粒子碰撞，在表面力的作用下粘在一起，形成更大的聚集体，这是进一步生长的种子。毫米级的碰撞主要是粘性相互作用。然而，亚毫米到毫米/厘米大小的尘埃和冰聚集体碰撞的结果到目前为止还不清楚，甚至在毫米/秒到厘米/秒的典型碰撞速度的圆盘中假设了一个emph（反弹障壁）。这可能会阻止进一步的生长（不再粘在一起），或者也可能是有益的（更大的物体清除小的聚集体）。因此，对行星形成的中间阶段还没有充分了解。最近发现，在实验室中，利用克努森压缩器效应将颗粒悬浮在表面上，可以实现亚毫米到几厘米的尘埃和冰颗粒在毫米/秒到厘米/秒范围内的自由碰撞。漂浮的尘埃和冰团之间以毫米/秒到厘米/秒的速度碰撞是经常可以观察到的（每秒几次），并且可以在无限的时间内获得粘滞、弹跳和破碎的概率以及它们的细节。因此，单次碰撞的细节，特别是由大量相互作用的尘埃或冰聚集体组成的系统向平衡状态的时间演化是可以通过实验获得的。在原行星盘的内缘和光学薄的部分，尘埃聚集体被主星照射。最近还发现，聚集体受到光致力的影响，从而加速了尘埃的形成。在实验室中有大量的自由悬浮聚集体，光电泳的研究是可能的。在这个项目中，我们在实验室中进行了有光致电泳影响和没有光致电泳影响的碰撞实验：第一次在实验室中很容易地获得数千个亚毫米到厘米的自由相互作用的尘埃和冰聚集体的时间演变，这里将详细研究。

Planetary formation takes place in accretion disks (protoplanetary disks) around newly formed stars. The early phase is dominated by collisional growth of dust and ice aggregates: The initially micron sized dust and ice particles collide, stick together by surface forces and form larger aggregates which are the seeds for further growth. Up to millimeter size collisions are dominated by sticky interactions. However, the outcome of collision of sub-mm to mm/cm sized dust and ice aggregates is till this date unclear, even a emph(boucing barrier) is postulated for the typical collision velocities in a disk of mm/s to cm/s. This might prevent further growth (no more sticking) or might also be beneficial (sweep-up of the small aggregates by larger bodies). Hence, the intermediate stage of planet formation is not sufficiently understood.It was recently discovered that free collisions of sub-mm to several cm dust and ice aggregates within the mm/s to cm/s regime can be realized in the laboratory by levitating aggregates over a surface by a Knudsen compressor effect. Collisions between the levitating dust and ice aggregates with mm/s to cm/s are frequently (several per second) observable and probabilities for sticking, bouncing and fragmentation and their details can be gained over unlimited periods of time. Hence, the details of single collisions and espacially the time evolution towards equilibrium states of a system of multitudes of interacting dust or ice aggregates are experimental accessible.At the inner edge and at the optically thin parts of protoplanetary disks dust aggregates are irradiated by the host star. It was also just recently discovered that aggregates are subject to a photophoretic force which accelerates the dust. Having multitudes of free levitating aggregates in the laboratory, studies of photophoresis are possible.In this project we carry out collision experiments in the laboratory with and without the influence of photophoresis: The time evolution of thousands of free interacting sub-mm to cm dust and ice aggregates is easily accessible in the laboratory for the first time which will be studied in detail here.