Dense Particle Clouds in Laboratory Experiments in Context of Drafting and Streaming Instability

Abstract

The streaming instability, as an example of instabilities driven by particle feedback on a gas flow, has been proven to have a major role in controlling the formation of planetesimals. These instabilities in protoplanetary disks occur at the transition from being gas-dominated to being dust and ice particle dominated. Here, we present experiments to approach this situation in the laboratory for particles in the Knudsen flow regime. In these experiments, we observe a particle cloud trapped for about 30 s in a rotating system under Earth’s gravity. For average dust-to-gas ratios up to 0.08, particles behave like individual test particles. Their sedimentation speed is identical to that of a single free-falling particle, even in locally denser regions. However, for higher dust-to-gas ratios, the motion of particles becomes sensitive to clumping. Particles in locally denser regions now sediment faster. Their sedimentation speed then depends linearly on the overall dust-to-gas ratio. This clearly shows a transition from tracerlike behavior to collective behavior. Beyond these findings, these types of experiments can now be used as a gauge to test particle feedback models in astrophysical hydrocodes, which are currently used for numerical simulations of streaming instabilities.

Planetesimals in rarefied gas: wind erosion in slip flow

“…This technique is called particle tracking velocimetry and is often used for gas flow characterizations at small ambient pressures (Musiolik et al 2018;Demirci et al 2019;Kruss et al 2019). We use the Fiji plug-in TrackMate as tracking tool (Schindelin et al 2012;Tinevez et al 2017) like Demirci et al (2019) and Schneider et al (2019). Sample spheres, which are lifted by the wind, couple to the gas and are accelerated in flow direction within the coupling time t c .…”

Laboratory Experiments on the Motion of Dense Dust Clouds in Protoplanetary Disks

“…The setup of the experiment (see fig. 1) follows the principle used in aggregation experiments by Poppe & Blum (1997) and Blum et al (1998), but is especially based on earlier experiments on dense clouds by Schneider et al (2019).…”

“…The friction time is calculated with equation 2. The experiments were carried out similar to the ones described in Schneider et al (2019). In short, the chamber was evacuated to a preset pressure and then disconnected from the vacuum pump.…”

“…In Schneider et al (2019), we studied the transition from test particle to collective behavior in a levitation experiment, analyzing the free-fall velocity of grains in a cloud. We empirically found that the sedimentation velocity depends on what we call sensitivity factor F S and the closeness C of the individual particle as…”

“…The sensitivity α connecting the solid-to-gas ratio to the sensitivity factor in eq. 5 was just a constant in Schneider et al (2019).…”