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 08-589. The award provides funds to partially support the graduate student participation in the overall research effort, which is being funded separately by the DoE [Grant DE-FG02-00ER54585OFES].
The nonlinear dynamics of strong interchange instabilities concern fundamental phenomenon occurring in a variety of natural and artificial situations. In this work, laboratory techniques will be used to produce intense interchange instabilities, induce strong interchange convection, and sustain steady interchange turbulence. The investigations focus on measurement, modification, and understanding of strong interchange turbulence. Previous work has found that interchange turbulence is dominated by large-scale rotating structures, and, probably, these structures represent a "self-organized" state. With this award, remaining questions concerning the precise nature of structure coupling and transport will be addressed with improved diagnostics, additional probes, and advanced simulations using our newly parallelized nonlinear interchange code. The combination of detailed experimental measurements, computer simulation, and computer data analysis will test developing theory and provide a basis for understanding a variety of nonlinear processes which occur in plasmas produced in the laboratory and found in nature.
The Collisionless Terrella Experiment (CTX) research project creates connections between laboratory plasma physics, natural plasma phenomena, nonlinear physics, and computational physics. CTX serves a central and important role in the educational opportunities for Columbia University graduate and undergraduate students. Undergraduate student research interns assembled the CTX device, and this project will continue to be a student-focused research program. This project attracts outstanding graduate and undergraduate students and has provided hands-on research experience to talented high school students.
This NSF award provides support for the Graduate Research Assistant involved with this research project.
Space and laboratory plasma confined by a strong magnetic field have remarkable properties. Low frequency mixing of the plasma occurs through the interchange of long plasma-filled tubes aligned with the magnetic field. The plasma dynamics becomes two-dimensional because these tubes can only move radially or circulate around the poles of the magnetic dipole. A unique property of two-dimensional fluids and plasmas is the formation of large swirls through the nonlinear combination of smaller swirls. For this project, new experiments using a "laboratory magnetosphere" at Columbia University revealed the structures, dynamics, and interactions of swirls of high-temperature plasma. Measurements were combined with computer simulations to understand electrostatic self-organization and successfully predict the multi-mode structure of interchange turbulence. Additionally, students were able to control the size of the rotating swirls by changing the voltage on multiple probes inserted into the plasma. Columbia University graduate students were the first to show both the natural and the driven "inverse cascade" of two-dimensional turbulence in a magnetized dipole plasma. Students demonstrated that smaller swirls grow to fill the whole size of the plasma. The new understanding from this project improves space weather models of planetary magnetospheres and reveals the fundamental nature of hot plasma confined by strong magnetic force fields. -- Additional information can be found in Grierson, et al., Phys. Rev. Lett., 105, 205004 (2010), in B. Grierson,et al., Phys Plasmas 16, 055902 (2009), and at www.apam.columbia.edu/ctx/ctx.html. -- Attached photograph shows the multiple-probe array used to measure and control the turbulent mixing of a laboratory magnetosphere. Right: Columbia University graduate student, Max Roberts, installing and calibrating the multiple-probe array within the Collisionless Terrella Experiment. Left: High-speed image of high-temperature plasma showing shadows of the probes against the visible emission from the plasma. The glow from nano-sized diamond dust grains are used to compute local turbulent plasma fluctuations. --
