Afterglow method of selectively removing larger dust particles to prepare a 2D layer in a plasma*

Dusty plasma experiments are often performed using a single horizontal layer of dust particles levitated in a capacitively coupled radio-frequency plasma discharge. Imaging such a layer using video microscopy allows experimental investigations of physics such as 2D shocks. In this talk, we demonstrate a method of preparing a 2D layer. Under the same conditions as one of our 2D shock experiments, we introduced 8.69 micron polymer spheres into a 13.5 mTorr argon plasma. To remove the heavier particles, and yield only a single layer of identically sized particles, we modulated the rf plasma, repeatedly turning it off for almost 1 ms of afterglow conditions followed by reigniting the plasma for about 5 or 10 microsec. This modulation method can be performed at the single touch of a button. Unwanted heavier particles selectively land on the lower electrode during the afterglow, and remain there so that they are removed. This process yields a layer of a single size of particles in the plasma.