My current research interest is plasma modeling and control for fusion reactors. Previously, I worked on the dynamics, control and optimization of space telescopy missions (TPF-C); Modelling of relative spacecraft motion & Nonlinear estimation theory.


Plasma Dynamics and Control

My research focuses on the application of dynamics and control theory to experimental plasma physics. I analyze the dynamics of complex plasma phenomena using applied mathematics and control theory with the aim of designing and implementing novel control techniques, which I then use to build real-time control systems from the ground up.

At DIII-D, I am leading the tearing mode suppression and avoidance experiments. In addition to the tearing mode physics, this project includes software and hardware development for the real-time electron cyclotron steerable mirror control. A new control system was built to direct the microwave power of the gyrotrons and suppress the plasma instabilities as they emerge. The task is achieved by fusing (1) measurements from multiple diagnostics such as motional Stark effect (MSE), Mirnov and Electron Cyclotron Emission (ECE) to identify the instabilities; (2) real-time density/temperature profile reconstruction; (3) real-time ray tracing to locate the power deposition location; (4) software for decision-making; and (5) control boards built in-house specifically for this purpose. I developed plasma divertor detachment and radiation control for DIII-D’s advanced scenarios by integrating the divertor Thompson, Dβ, Dγ, bolometry and interferometry diagnostics. I developed “snowflake” advanced divertor scenarios. I implemented real-time snowflake calculation and control to obtain and stabilize different snowflake configurations. I implemented and commissioned burn control with non-axisymmetric coils. This includes the real-time βN control with I/C coils and pedestal density control using Thomson data acquisition.

At NSTX, I implemented system identification based models and an online automatic control tuning algorithm to successfully develop a multi-dimensional shape control algorithm that combined the strike point and x-point, squareness, radial and vertical controls. I also worked on developing rotation control using neutral beams and non-axisymmetric coils, which apply neoclassical toroidal viscosity, as actuators.

At KSTAR tokamak, located in Daejon, Korea, I implemented a new vertical position and shape control in collaboration with colleagues, which enabled the first 10-second H-mode plasma operation with a double null divertor and achieved stable operations at an elongation of 2.1. See the publications for more information.

The Dynamics, Control and Optimization of a Constellation of Spacecraft for a Planet-Finding Mission

It is likely that the next decade will see NASA launch the first in a series of missions dubbed the Terrestrial Planet Finders to detect, image, and characterize extrasolar earthlike planets. One promising concept involves the formation flying of a conventional space telescope in a Sun-Earth L2 Halo orbit, with multiple large occulters, to block the light of a star and allow imaging of its dim, close-by planetary companion. This approach to planet imaging eliminates all of the precision optical requirements that exist in the alternate coronagraphic or interferometric approaches. The scientific challenge is moved to the area of precise dynamics and control.
My graduate dissertation addresses the three main challenges of the Terrestrial Planet Finder-Occulter Mission: the dynamics of the satellite formation, the control and trajectory design of the satellites, and the global optimization of the mission. I developed new numerical algorithms to find the invariant structures where the spacecrafts can be placed to give maximum sky coverage and the option of imaging a greater number of planetary systems. I also solved the optimal control problem for the trajectory of each spacecraft while they are moving between target stars, and, finally, I solved the global optimization problem for different criteria such as fuel consumption and time. See the publications for more information.

Periodic Relative Orbits for Formation Flying Around Earth

We adopted a Hamiltonian approach to relative motion and found canonical constants termed "epicyclic elements". We then looked at the various effects of perturbations. Here you can find an .m file of the solution of the periodic orbits for eccentric motion which we found using this method. In a recent publication, I looked at the effects of J2, J3 and J4 perturbations on periodic orbits as well. See the publications for more information.

Particle and Nonlinear Filtering for Manuvering Target

Part of an SBIR grant, I am looking at the filtering of an interceptor mission with a weaving target using different types of particle and nonlinear filters. See the publications for more information.