原行星尘埃凝聚物的物理学。五、速度超过碎裂阈值时多尘团块的多重影响
The Physics of Protoplanetesimal Dust Agglomerates. V. Multiple Impacts of Dusty Agglomerates at Velocities Above the Fragmentation Threshold
摘要：
在过去的几年里，实验表明，碰撞以上的碎裂阈值速度是一个潜在的重要增长过程的原行星尘埃聚集。为了更深入地了解这一过程，我们进行了实验室和落塔实验，研究烧结粉尘目标上的小，多孔粉尘聚集体弹丸的多次影响。射弹和靶由1.5微米单分散、球形SiO2单体组成，体积填充因子为0.15（射弹）和0.45（靶）。炮弹由螺线管磁铁加速，并与弹匣结合，弹匣可以在真空中对目标上的同一点进行25次撞击。我们测量的质量吸积效率和体积填充因子为不同的冲击速度之间的1.5和6.0米/秒。最低撞击速度的实验是在微重力条件下在不来梅落塔中进行的。在此速度范围内，我们发现吸积效率随速度的增加而线性增加。在实验室实验中，吸积效率从0.12增加到0.21（单位弹丸质量）。记录的撞击图像表明，从弹丸到靶的质量转移导致靶上的锥形结构的生长。从图像中，我们还测量了生长结构的体积填充因子，随着冲击速度的增加，其范围从0.15（未压实）到0.40（显著压实）。这些结果增加了我们对原行星盘中聚集体生长的认识，并应考虑到未来的原行星尘埃生长模型。
英文摘要：
In the last years, experiments have shown that collisions above the fragmentation threshold velocity are a potentially important growth process for protoplanatary dust aggregates. To obtain deeper understanding of this process, we performed laboratory and drop-tower experiments to study multiple impacts of small, porous dust-aggregate projectiles onto sintered dust targets. Projectile and target consisted of 1.5 micron monodisperse, spherical SiO2 monomers with volume filling factors of 0.15 (projectiles) and 0.45 (targets). The projectiles were accelerated by a solenoid magnet and combined with a magazine with which 25 impacts onto the same spot on the target could be performed in vacuum. We measured the mass-accretion efficiency and the volume filling factor for different impact velocities between 1.5 and 6.0 m/s. The experiments at the lowest impact speeds were performed in the Bremen drop-tower under microgravity conditions. Within this velocity range we found a linear increase of the accretion efficiency with increasing velocity. In the laboratory experiments, the accretion efficiency increases from 0.12 to 0.21 in units of the projectile mass. The recorded images of the impacts showed that the mass transfer from the projectile to the target leads to the growth of a conical structure on the target. From the images we also measured the volume filling factors of the grown structures, which ranged from 0.15 (uncompacted) to 0.40 (significantly compacted) with increasing impact speed. These results augment our knowledge of the aggregate growth in protoplanetary disks and should be taken into account for future models of protoplanetary dust growth.
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