RUI: Studies of Particle Transport in a Non-Neutral Plasma Trap

Occidental College, Los Angeles CA

Investigators

Abstract

This award is made in response to a proposal submitted to and reviewed under the NSF/DOE Partnership in Basic Plasma Science and Engineering joint solicitation NSF 09-596. The award provides funds to support undergraduate participation in the overall research effort, which is being funded separately by the DOE under contract to Occidental College (Grant DE-FG02-06ER54882). This project studies electron transport in a cylindrical non-neutral plasma trap due to the presence of applied asymmetric electric fields. Previous work on this project found some superficial agreement with theory, but also identified significant areas of disagreement. The work of this grant will focus on testing a new model for the transport based on previous experimental and simulation results. In this model, the transport is dominated by low velocity, axially trapped particles that are scattered through a chaotic, collisionless process. To test this model, experiments will be performed to measure and manipulate the trapped particles. To further refine the model, transport at the low asymmetry frequencies will be studied where the experiments diverge most dramatically from resonant particle theory. Finally, this work will be supported with a simple particle simulation which will be extended to focus on previously observed chaotic dynamics. The experimental work is performed in a specially designed trap in order to avoid previously encountered complications and to test transport theory under simple conditions. The spectrum of the field asymmetry is simplified by using up to forty wall sectors to create it. The electron density is reduced by a factor of 100 to reduce non-essential complications due to collective effects, while a biased wire running along the axis of the trap produces a radial electric field which maintains the azimuthal drift normally present in higher density plasmas. Electron position and density are determined by dumping the electrons from the trap onto a phosphor-coated screen and analyzing the resultant image. Experimental transport fluxes are then calculated from the time evolution of these images and compared to theoretical models. There are several broader impacts of the activities. Occidental College is a national leader in the area of undergraduate research participation and has been recognized for its integration of research and education. As in previous years, undergraduate students will be involved as participants and co-workers in this research, and these students will present the results of their research at local and regional meetings. Because Occidental is one of the most diverse of national liberal arts colleges, students from underrepresented groups are likely to be members of the research groups. Dissemination of results will be broadened beyond the usual publication venues and papers given at the annual APS/DPP meeting by participation in the multidisciplinary Workshop on Non-Neutral Plasmas (held every two to three years) and by developing a web site. Finally, there are also scientific broader impacts to this research. This project advances understanding of plasmas by testing a fundamental theory of plasma transport and will benefit any application that requires the containment and manipulation of non-neutral plasmas. An understanding of the complex issues involved in neo-classical transport is also of value in conventional (neutral) confinement devices. The NSF support of undergraduate participation adds a broader educational impact through the early-year training of students by introducing them to scientific research as a possible career path.