Experimental and Computational Investigation of the Dynamics of Fluctuation Suppression by Controlled Flow Shear

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The goal of this research is to investigate experimentally the detailed dynamics of transitions between states of unstable drift fluctuations (including broadband turbulence), and fluctuation-suppressed states in a controlled laboratory environment. These experiments will be complemented by direct comparisons with a nonlinear fluid turbulence code, adapted specifically to model this experiment. The proposed experiments will take place in the dual-source HELCAT (HELicon-CAThode) device at the University of New Mexico (UNM). HELCAT is a flexible device that provides unique capabilities important to these experiments. The two plasma sources- operated independently or simultaneously - can generate plasmas with edge fluctuations ranging from single drift modes to broadband drift turbulence. Additionally, plasma biasing to affect Er × Bz flow profiles has been demonstrated, and collisionality, important in drift wave damping, has been varied by more than an order of magnitude. The numerical code developed by the co-PI at the University of Alaska Fairbanks, a 2-D fluid slab model of electrostatic fluctuations with detailed diagnostics to understand the dynamics of the interaction between the fluctuating modes, will be modified to allow the drive to mimic the experimental drive. The code has an external flow that can be turned on to look at the impact of flow on the fluctuating modes.The research facility is well suited for training students for careers in fusion energy or studying turbulent transport in plasmas, a process important in space and astrophysical plasma as well as magnetically confined laboratory plasmas. The research could have a significant impact on efforts to create predictive models for turbulent transport in plasmas. This research is relevant to basic plasma physics, complex dynamics, space plasmas and magnetically confined plasmas.This proposal was submitted to the NSF-DoE Partnership in Plasma Science and Engineering joint solicitation 08-589. This award is being funded by the Division of Physics of the Mathematical and Physical Sciences Directorate.