1 Abstract—Dust aggregates in complex plasmas have been studied theoretically in computer models, but not extensively in an experimental setting. This work investigates several properties of aggregates which are responsible for dust dynamics: charge, dipole moment, and gas drag. A diode pumped laser is used to perturb aggregates in a GEC rf reference cell, and a high-speed camera acquires image data. Particle trajectories are extracted and analyzed to characterize or estimate values of the properties under investigation. Index Terms—Aggregates, Dipole moment, Dust charge, Dusty plasma, Gas drag. I. INTRODUCTION usty plasmas can be found in such diverse celestial environments as comet tails, planetary rings, and interstellar clouds [1]. Small, micrometer-sized dust particles in plasma can collide under certain conditions to form aggregate structures. Charged dust aggregates play an important role in many astrophysical phenomena, such as early stages of protostellar and protoplanetary growth, the dynamics of planetary rings and cometary tails, and the formation of noctilucent clouds in earth’s upper atmosphere [2]. Dust is also expected to be an unwanted byproduct in the operation of plasma fusion devices, such as ITER [3]. In all of these environments, direct study of the dust aggregates in their in situ environment is extremely difficult, if not impossible. As a model for these complex plasma environments, dust aggregates are formed in a laboratory plasma as monodisperse spheres are accelerated in a self-excited dust density wave. Individual dust particles are perturbed using a diode pumped Manuscript received August 2012. This work was supported in part by the National Science Foundation under Grant No. 0847127 through the Research Experience of Undergraduates program. This work was also supported by the Baylor Department of Physics. Allen B. Davis is an undergraduate at Williams College, Williamstown, MA 01267 USA, and was a participant in the REU program (e-mail: allen.b.davis@williams.edu). Jorge Carmona-Reyes is with the Center for Astrophysics, Space Physics & Engineering Research, Baylor University, Waco, TX. 76798 USA (e-mail: Jorge_Carmona@baylor.edu). Lorin S. Matthews is with the Physics department at Baylor University, Waco, TX 76798 (email: Lorin_Matthews@baylor.edu). Truell W. Hyde is with the Center for Astrophysics, Space Physics & Engineering Research, Baylor University, Waco, TX. 76798 USA (phone: 254-710-3763, fax: 254-710-7309, e-mail: Truell_Hyde@baylor.edu). solid state laser (coherent VERDI) with their motions recorded by a high-speed camera. Analysis of the particle motion allows determination of the aggregate characteristics, such as charge, mass, and gas drag. Although these quantities have been studied in computer models [2], little experimental data has been acquired and analyzed to date. II. THEORY A. Charging A dust aggregate acquires an electric charge by colliding with the constituent electrons and ions in the plasma. Electrons in the plasma have a significantly greater velocity than the ions due to their lower mass. Thus an aggregate experiences a greater flux of electrons than ions, giving the aggregate a negative charge. The aggregate’s negative charge will eventually repel incoming electrons at the same rate that it attracts ions, leading to an equilibrium charge. An aggregate’s electric charge affects its interactions with other nearby aggregates in the plasma as well. Since aggregates tend to all be charged negatively, they resist collisional growth. However, high velocities can allow aggregates to overcome their electrostatic repulsion and collide and stick [4]. B. Levitation In this experiment, a GEC rf (Gaseous Electronics Conference radio frequency) reference cell is used to study dust aggregate interactions in plasma under laboratory conditions. A description of this setup and relevant terminology can be found in [5]. Dust introduced to the Dynamics of Dust Aggregates in a Complex Plasma Allen B. Davis, Jorge A. Carmona-Reyes, Lorin S. Matthews, and Truell W. Hyde Center for Astrophysics, Space Physics and Engineering Research, Baylor University, Waco, Texas 76798-7310, USA D Fig. 1. This drawing depicts the three aggregate interactions studied in this work: (a) is the electrostatic repulsion of two negatively charged aggregates, (b) is the dipole interaction of two aggregates with a charge distribution, and (c) is the deceleration of an aggregate due to gas drag.