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 support undergraduate participation in the overall research effort, which is being funded separately by the DoE under contract number DE-FG02-09ER55022.
This research aims to investigate active control of unstable fluctuations, including fully developed turbulence and the associated cross-field particle transport, via manipulation of flow profiles in a magnetized laboratory plasma device. Fluctuations and particle transport will be monitored by an array of electrostatic probes, and flow profiles controlled via a set of biased concentric ring electrodes that terminate the plasma column. The goals of the proposed research are threefold. 1. to develop a predictive code to simulate plasma transport in the linear HELCAT (HELicon-CAThode) plasma device at the University of New Mexico (UNM), where the experimental component of the proposed research will be carried out. 2. to establish the feasibility of using advanced model-based control algorithms to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles. 3. to investigate the fundamental nonlinear dynamics of turbulence and transport physics.
The outcome of the proposed research, although focused on basic plasma physics, will have a strong impact on the scientific advancements that are needed to make nuclear fusion a viable source of energy, and will therefore produce a profound impact on an area of immense importance to the welfare of society. The proposed research will advance discovery while promoting teaching and learning. Due to its multidisciplinary nature, the proposed research plan brings together concepts from plasma physics, computational methods, and controls, with emphasis on experimental validation of the proposed modeling and control solutions. Graduate and undergraduate students will benefit from this unique multidisciplinary experience that will enhance their ability to conduct advanced research, think creatively, take advantage of unique facilities making good use of collaborative arrangements, and work in an individual capacity and as members of a team. The infrastructure for research and learning will be enhanced in each one of the collaborating institution. This collaboration will grant access to graduate and undergraduate students to the HELCAT experimental facility, where they can conduct experiments to validate the modeling and control solutions that result from their research, and will expose each one of the participating students to new research areas.
The 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.
Turbulence, and turbulence-driven transport are ubiquitous in magnetically confined plasmas, where there is an intimate relationship between turbulence, transport, instability-driving mechanisms (such as gradients), plasma flows, and flow shear (including both externally imposed mean flows and self-generated flows (zonal flows)). Though many of the detailed physics of the interrelationship between turbulence, transport, drive mechanisms, and flow remains unclear, there have been many demonstrations that transport and/or turbulence can be suppressed or reduced via manipulations of plasma flow profiles. This is well known in magnetic fusion plasmas [e.g., high confinement mode (H-mode) and internal transport barriers (ITB’s)], and has also been demonstrated in laboratory plasmas. A substantial theoretical and experimental physics effort has been going on for decades to develop predictive models for the time evolution of profiles (densities, temperatures, currents, velocities, etc.) in plasmas. The strong coupling between the different physical variables involved in the plasma transport phenomenon and the high complexity of its dynamics call for a model-based, multivariable approach to profile control where those predictive models could be exploited. Simply stated, the dynamics of the plasma profile response to the different actuators must be taken into account during the control design process. Present state of the art in the area of profile control in plasmas shows much room for improvement and many challenges ahead. Profile control in plasmas can take great advantage of recent developments in the field of (nonlinear) control of distributed-parameter systems. Therefore, since the plasma physics and control tools may now be in hand, it has been proposed by a collaborative team of researchers from Lehigh University (LU), University of New Mexico (UNM) and University of Montana (UM) to investigate active control of unstable fluctuations, including fully developed turbulence and the associated cross-field particle transport, via manipulation of flow profiles in a magnetized laboratory plasma device. Fluctuations and particle transport can be monitored by an array of electrostatic probes, and E×B flow profiles can be controlled via a set of biased concentric ring electrodes that terminate the plasma column in the linear HELCAT (HELicon-CAThode) plasma device at UNM. The goals of the proposed research have been threefold: i- to develop a predictive code to simulate plasma transport in HELCAT, where the experimental component of the proposed research has been carried out; ii- to establish the feasibility of using advanced model-based control algorithms to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles; iii- to investigate the fundamental nonlinear dynamics of turbulence and transport physics. The LU Plasma Control Group has been primarily responsible for control-oriented modeling and model-based control design. Both non-model-based extremum-seeking open-loop control algorithms and model-based optimal closed-loop control algorithms haven been developed and validated by the LU Plasma Control Group. In addition to the PI, two graduate students and two undergraduate students, recruited through the National Science Foundation Research Experience for Undergraduate (REU) program, have participated in this project at LU. The outcome of the proposed research, although focused on basic plasma physics, has a strong impact on the scientific advancements that are needed to make nuclear fusion a viable source of energy, and will therefore impact an area of immense importance to the welfare of society as a whole. The proposed research has advanced discovery while promoting teaching and learning. Due to its multidisciplinary nature, the proposed research plan has brought together concepts from plasma physics, computational methods, and controls, with emphasis on experimental validation of the proposed modeling and control solutions. Graduate and undergraduate students have benefited from this unique multidisciplinary experience that has enhanced their ability to conduct advanced research, think creatively, take advantage of unique facilities making good use of collaborative arrangements, and work in an individual capacity and as members of a team. The infrastructure for research and learning has been enhanced in each one of the collaborating institutions. This collaboration has granted access to the HELCAT experimental facility to both graduate and undergraduate students, where they have conducted experiments to validate the modeling and control solutions resulting from their research, and has exposed each one of the participating students to new research areas. Outcomes of the proposed research have been disseminated broadly through conference presentations and journal publications.
