Engineering
Control of the Current Profile Evolution During the Ramp-Up Phase at DIII-D
Setting up a suitable current profile has been demonstrated to be a key condition for advanced scenarios with improved confinement and possible steady-state operation. Experiments at DIII-D focus on creating the desired q profile during the plasma current ramp-up and early attop phases with the aim of maintaining this profile during the subsequent phases of the discharge. Active feedback control of the q profile evolution at DIII-D has already been demonstrated [1], and an open-loop control scheme has been proposed [2] based on a simplified control-oriented dynamic model [3]. The use of Corsica for both control testing and design is reported, and results of open-loop current profile control experiments are presented.
[1] J.R. Ferron, et al., Nucl. Fusion 46 (2006) L13.
[2] Y. Ou, et al., Proc. American Control Conf., New York (2007).
[3] Y. Ou, et al., Fusion Eng. & Design 82 (2007) 1153.
Model-Based Shape Control Design for the National Spherical Torus Experiment (NSTX)
Plasma shape and position control is a challenging problem due to the difficulties associated with real-time shape identification, plasma parameters measurement, and control method selection. The recent implementation of the real-time equilibrium reconstruction code rtEFIT on NSTX allows plasma shaping by controlling the magnetic flux at the plasma boundary. A non-model-based shape controller that exploits this capability has been recently proposed [1]. We describe current efforts to develop a robust model-based multi-input-multi-output (MIMO) H∞ controller to provide real-time shaping and position control in the presence of disturbances and uncertainties in the plasma parameters. The control design is based on linear plasma response models derived from fundamental physics assumptions. Computer simulation results illustrate the performance of the model-based shape control method.
[1] D.A. Gates, et al., Nucl. Fusion 46 (2006) 17–23.
*Supported by the Pennsylvania Infrastructure Technology Alliance (PITA), the NSF CAREER award program (ECCS-0645086), and US DOE DE-FG03-99ER54522.
A Simple Gasifier Model That Runs in Aspen Dynamics
Gasification has been used in industry on a relatively limited scale for many years, but it is immerging as the premier unit operation in the energy and chemical industries. The switch from expensive and insecure petroleum to solid hydrocarbon sources (coal and biomass) is occurring due to the vast amount of domestic solid resources, national security and global warming issues. Gasification (or partial oxidation) is a vital component of “clean coal” technology. Sulfur and nitrogen emissions can be reduced, overall energy efficiency is increased and carbon dioxide recovery and sequestration are facilitated. Gasification units in an electric power generation plant produce a fuel gas for driving combustion turbines. Gasification units in a chemical plant generate synthesis gas, which can be used to produce a wide spectrum of chemical products. Future plants are predicted to be hybrid power/chemical plants with gasification as the key unit operation. › Continue reading
Materials for Reversible High Temperature Chemisorption of CO2
Results of experimental tests into the equilibrium and column dynamic data for the chemisorption of CO2 on two materials has identified the materials as potential candidates for the capture of CO2. The first of the materials is a K2CO3 – promoted hydrotalcite that displays good sorption capacity in 400-500 C range. The second is a Na2O -promoted alumina that has shown good sorption capacity in 250-400 C temperature range. The two materials both exhibited Langmuirian behavior in the low pressure region, but deviated substantially in higher pressure regions. A new analytical model that simultaneously accounts for Langmuirian chemisorption and an additional surface complexation reaction between gaseous and sorbed CO2 has been proposed to describe the measured equilibrium data for both materials. Experimental breakthrough tests showed fast kinetics and narrow mass transfer zones for CO2 adsorption. The isosteric heats of chemisorption and heats of additional complexation reaction on both materials were estimated to be low, indicating that desorption of CO2 from both materials could be achieved with relative ease. Tests have confirmed that both materials show stable sorption capacity after several sorption-desorption cycles. These characteristics make them attractive candidates for use in cyclic processes for the capture of CO2. The Na2O promoted alumina shows promise as a candidate for capture of CO2 from flue gas of a coal fired power plant, while the K2CO3 promoted hydrotalcite will be a better candidate for the Sorption Enhanced Reaction process to simultaneously produce fuel cell grade H2 and high purity CO2 at feed gas pressure.
Trapping and releasing of telecom rainbow
We show how the graded grating structures developed for “trapped rainbow” in THz domain can be transferred to telecom frequencies for future possible optical communication and various nano photonic applications.