Punctuating Instability of~a 2D Dusty Plasma Colloidal Crystal

When placed in a weakly-ionized RF plasma,~colloidal microparticles~can be trapped in the~narrow Debye~sheath region above a~capacitively-coupled electrode. Known as a ''dusty plasma", the particles become negatively charged, leading to the formation of large, 2D~crystalline monolayers.~At low pressures the particles can~experience vertical oscillations due to plasma density fluctuations in the sheath. As a result of these fluctuations, we have~found that at low pressures and low bias~voltage, the colloidal crystal~experiences temporally reoccurring instabilities. Such "punctuating"~instabilities are caused by the~redistribution of kinetic energy from~vertical vibrations~to horizontal motion, essentially melting the crystal into a gas-like state. After the incipient instability, without changing any external parameters, the system loses kinetic energy to damping with the surrounding gas, then~eventually~recrystallizes and~remains stable until next punctuating instability. The period of the instability~ranges from seconds to minutes depending on the system parameters, and can vary significantly within a given system. Using simple simulations of 2D crystals driven by a~vertical Langevian forcing, we are able to capture the salient features of the punctuating instability.