Brian Lynch

Observations of imposed ordered structures in a dusty plasma at high magnetic field

Dusty plasmas have been studied in argon, rf glow discharge plasmas at magnetic fields up to 2 T, where the electrons and ions are strongly magnetized. In this experiment, plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper, electrically floating electrode supports a semi-transparent, titanium mesh. We report on the formation of an ordered dusty plasma, where the dust particles form a spatial structure that is aligned to the mesh. We discuss possible mechanisms that may lead to the formation of the “dust grid” and point out potential implications and applications of these observations.

The magnetized dusty plasma experiment (MDPX)

The magnetized dusty plasma experiment (MDPX) is a newly commissioned plasma device that started operations in late spring, 2014. The research activities of this device are focused on the study of the physics, highly magnetized plasmas, and magnetized dusty plasmas. The design of the MDPX device is centered on two main components: an open bore, superconducting magnet that is designed to produce, in a steady state, both uniform magnetic fields up to 4 Tesla and non-uniform magnetic fields with gradients of 1–2 T m−1 and a flexible, removable, octagonal vacuum chamber that provides substantial probe and optical access to the plasma. This paper will provide a review of the design criteria for the MDPX device, a description of the research objectives, and brief discussion of the research opportunities offered by this multi-institution, multi-user project.

Quasi-discrete particle motion in an externally imposed, ordered structure in a dusty plasma at high magnetic field

Dusty plasmas have been studied in argon, radio frequency (rf) glow discharge plasmas at magnetic fields up to 2.5 T where the electrons and ions are strongly magnetized. Plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper electrode supports a dual mesh consisting of #24 brass and #30 aluminum wire cloth. In this experiment, we study the formation of imposed ordered structures and particle dynamics as a function of magnetic field. Through observations of trapped particles and the quasi-discrete (i.e., “hopping”) motion of particles between the trapping locations, it is possible to make a preliminary estimate of the potential structure that confines the particles to a grid structure in the plasma. This information is used to gain insight into the formation of the imposed grid pattern of the dust particles in the plasma.

Preliminary characteristics of magnetic field and plasma performance in the Magnetized Dusty Plasma Experiment (MDPX)

The Magnetized Dusty Plasma Experiment (MDPX) device is a newly constructed research instrument for the study of dusty (complex) plasmas. The MDPX device is envisioned as an experimental platform in which the dynamical behavior of all three charged plasma components, the electrons, ions, and charged microparticles (i.e., the ‘dust’) will be significantly influenced by the magnetic force. This brief paper will provide a short overview of the design, magnetic performance, and initial plasma measurements in the MDPX device.

Vertical oscillations of dust particles in a strongly magnetized plasma sheath induced by horizontal laser manipulation

Experimental studies are presented where dust particles are suspended in the lower sheath region of an argon rf discharge at a strong vertical magnetic field from B=1.5 T up to 2.27 T. There the particles arranged in an ordered pattern imposed by the upper mesh electrode. It is observed that the particles jump to a new equilibrium position, where they exhibit self-excited vertical oscillations when illuminated by a horizontal laser beam. The dust motion is weakly damped during an upward jump and strongly damped during the return to the equilibrium after the laser is switched off. A model based on delayed charging is presented that can describe the observed behavior.

Real-Time Particle Tracking in Complex Plasmas

Complex plasmas contain, in addition to the usual electrons, ions, and neutral atoms, macroscopic electrically charged (nanometer to micrometer) sized dust particles. Based on the ratio of the electrostatic potential to kinetic energy, these microparticles can exhibit gaseous, fluid, and crystal-like behavior. For this reason, complex plasmas are a unique testing ground to study multiparticle systems. The dynamics of these systems can be studied using the particle tracking velocimetry (PTV) analysis technique. The PTV technique provides a spatially resolved particle phase space distribution function, which can be used to calculate correlation functions and thermal properties of the system. There are experimental settings, such as microgravity experiments, where technical and data storage limitations make it desirable to have near real-time video analysis techniques that allow an experimenter to tune operating conditions until appropriate velocity profiles or velocity distributions are obtained. This article discusses PTV software that allows for real-time particle tracking that, we believe, can be applied to a broad range of physical systems.