Improved Reproducibility of Plasma Discharges via Physics-model-based q-profile Feedback Control in DIII-D
26th IAEA Fusion Energy Conference
Kyoto, Japan, October 17-22, 2016
| Abstract |
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Recent experiments on DIII-D demonstrate the potential of physics-model-based q-profile control to improve reproducibility of plasma discharges. A combined feedforward + feedback control scheme is employed to optimize the current ramp-up phase by consistently achieving target q profiles (Target 1: qmin = 1.3, q95 = 4.4; Target 2: qmin = 1.65, q95 = 5.0; Target 3: qmin = 2.1, q95 = 6.2) at prescribed times during the plasma formation phase (Target 1: t = 1.5 s; Target 2: t = 1.3 s; Target 3: t = 1.0 s). At the core of the control scheme is a nonlinear, first-principles-driven, physics-based, control-oriented model of the plasma dynamics valid for low confinement (L-mode) scenarios. To prevent undesired L-H transitions, a constraint on the maximum allowable total auxiliary power is imposed in addition to the maximum powers for the individual heating and current-drive sources. Experimental results are presented to demonstrate the effectiveness of the combined feedforward+feedback control scheme to consistently achieve the desired target profiles at the predefined times. These results also show how the addition of feedback control significantly improves upon the feedforward-only control solution by reducing the matching error and also how the feedback controller is able to reduce the matching error as the constraint on the maximum allowable total auxiliary power is relaxed while keeping the plasma in L-mode.