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Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

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ing and design include computational tools <strong>for</strong> producing control-level models and simulations,<br />

ideally derived from more complex models, and control-level and intermediate-level simulations.<br />

These will enable development and testing of control algorithms and verification of real-time implementations.<br />

models required include all elements of a fusion plant system: relevant plasma responses,<br />

actuator responses to commands, diagnostic signal mappings to relevant physics, etc.).<br />

integrated, comprehensive plasma and plant simulations will also be needed, primarily <strong>for</strong> discovery<br />

of emergent phenomena, unexpected interactions, commissioning, per<strong>for</strong>mance and reliability<br />

quantification, and certification. Real-time predictive models will be needed <strong>for</strong> on-line<br />

operating point identification, controller adjustment and re-design, stability boundary proximity<br />

identification and so on. models and simulations must be validated against relevant experimental<br />

data to confirm the required accuracy.<br />

aLgORitHMS anD aPPROaCHES<br />

The requirement of producing quantifiably high-per<strong>for</strong>mance operational solutions requires research<br />

to produce novel control algorithms. This research includes mathematical solutions <strong>for</strong><br />

nominal high-per<strong>for</strong>mance control, as well as supervisory and off-normal response algorithms<br />

with provable reliability. control schemes must be developed <strong>for</strong> all required regulated parameters<br />

and stabilized modes, including multi-physics integrated schemes where appropriate. design<br />

tools and solutions must be developed to produce the necessary real-time, model-based control<br />

algorithms (mathematical control solutions) with associated gains, point designs, and provable<br />

high confidence per<strong>for</strong>mance.<br />

as a specific example of the control research needed, a reactor design that operates near stability<br />

limits to achieve high per<strong>for</strong>mance will require active suppression of tearing modes. Present-day<br />

research has demonstrated the need <strong>for</strong> complex nonlinear control algorithms to locate and align<br />

current deposition regions with relevant magnetic islands, to synchronize modulated current<br />

with the island phase, and to sustain the alignment and phase synchronization as plasma conditions<br />

evolve. The corresponding algorithms used in a reactor must be much more robust than<br />

present solutions, and must operate correctly and effectively upon first-time use. at the same<br />

time, the relative leverage provided by heating and current drive systems in self-heated burning<br />

plasmas will be much smaller. These requirements necessitate a robust design based on high accuracy<br />

models: the task is beyond the capability of empirical tuning, and in any case little opportunity<br />

will exist in the commissioning process to achieve such tuning. mathematical control design<br />

methods can guarantee a specified level of reliability and robustness, based on the accuracy and<br />

reliability of the models on which the design is based, and can squeeze maximum effectiveness<br />

from limited actuators. in exactly the same way as envisioned <strong>for</strong> fusion reactors, model-based<br />

design of complex multivariable control algorithms is what enables modern commercial aircraft<br />

to fly well and safely in their first flight tests, and indeed in all of their commercial flight operations.<br />

tRaNSiENt plaSMa EvENtS: additioNal RESEaRch REquiREMENtS<br />

Overall goal: Understand the underlying physics and control of high-per<strong>for</strong>mance magnetically<br />

confined plasmas sufficiently so that “off-normal” plasma operation, which could cause cat-<br />

98

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