DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 204: Model-based Closed-loop Current Profile Control at DIII-D | ||
| Name: | Eugenio Schuster
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Affiliation: | Lehigh University |
| Research Area: | Model based Control | Presentation time: | Requested | Co-Author(s): | John Ferron, Tim Luce, Mike Walker, Dave Humphreys, Tom Casper, Bill Meyer, Yongsheng Ou |
| Description: | The objective of this experiment is to implement closed-loop controllers developed for the regulation of the q profile evolution during the early phase of the discharge, including ramp-up and beginning of the flattop, with the ultimate goal of achieving a desired target profile at some time during the first part of the flattop phase. It is expected that closed-loop controllers will add robustness to previously tested open-loop controllers. | ||
| Experimental Approach/Plan: | The closed-loop control will regulate in real-time three actuators (total plasma current, average plasma density, and non-inductive current drive (NBI, ECH) power) based on real-time measurements of poloidal flux or current. We will assess the ability of the closed-controller to drive the current profile from an initial condition different from (but close to) the nominal one to a specific target profile. Different initial and target profiles will be considered mainly in L-mode but we also intend to carry out part of the experiment in H-mode.
Note: A separate proposal is being submitted to validate simplified control-oriented models and to test open-loop model-based control strategies for current profile regulation. Our goal is to carry out these closed-loop experiments late in the experimental campaign, after the model validation and open-loop control testing experiments. | ||
| Background: | Setting up a suitable current profile has been demonstrated to be a key condition for the achievement of advanced scenarios with improved confinement and possible steady-state operation. The current approach at DIII-D focuses on creating the desired current profile during the plasma current ramp-up and early flattop phases with the aim of maintaining this target profile during the subsequent phases of the discharge.
The development of model-based current profile controllers aims at saving long trial-and-error periods of time currently spent by fusion experimentalists trying to manually adjust the time evolutions of the actuators to achieve the desired current profile at some pre-specified time during the early flattop phase. A simplified dynamic model describing the evolution of the poloidal flux, and therefore the q profile, during the inductive phase of the discharge has been proposed. This model will be validated early in the experimental campaign and used for the synthesis of closed-loop current profile controllers. Closed-loop controllers have been and are being designed by obtaining a reduced order model from the original simplified control-oriented infinite-dimensional model through the Proper Orthogonal Decomposition (POD) technique. The reduced-order model is combined with Optimal Control theory for bilinear systems to synthesize closed-loop controllers. Based on initial results obtained in simulation studies, it is anticipated that the scheme can play an important role in fusion plasma physics experiments at the DIII-D tokamak. | ||
| Resource Requirements: | Machine time: 0.5 day
Note: Some coordination with the Steady-State Scenario group might allow use of piggybacks or individual shots on their experimental days. Beams, ECH. | ||
| Diagnostic Requirements: | Core and tangential Thomson, CER, CO2, magnetics, MSE, ECH diagnostics, a reasonable set of fast ion instability diagnostics (UF interferometers, FIR scattering, ECE at 500 kHz, fast magnetics with fast delay set in the current ramp), FIDA. | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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