Robust Burn Control in ITER Under Deuterium-Tritium Concentration Variations in the Fueling Lines
A. Pajares, E. Schuster
27th IAEA Fusion Energy Conference
Gandhinagar, India, October 22-27, 2018
Abstract
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Tight regulation of the burn condition in ITER has been proven possible
in simulations even under time-dependent variations in the fuel
concentration by the use of robustification techniques. One of the most
fundamental control problems arising in ITER and future burning-plasma
tokamaks is the regulation of the plasma temperature and density to
produce a determined amount of fusion power while avoiding possible
thermal instabilities. Such problem, known as burn control, will require
the development of controllers that integrate all the available actuators
in the tokamak. Moreover, the complex dynam- ics of the burning plasma
and the uncertain nature of some of its magnitudes suggest that nonlinear,
robust burn controllers will be necessary. Available actuators in the
burn control problem are auxiliary power modulation, fueling rate modulation,
and impurity injection. Also, recent experiments in the DIII-D tokamak
have shown that in-vessel coil-current modulation can be used for burn
control purposes. The in-vessel coils generate non-axisymmetric magnetic
fields that have the capability to decrease the plasma-energy confinement
time, which allows for regulating the plasma energy during positive energy
perturbations. In this work, in-vessel coil-current modulation is included
in the control scheme, and it is used in conjunction with the other
previously mentioned actuators to design a nonlinear burn controller which
is robust to variations in the deuterium-tritium concentration of the
fueling lines. Furthermore, fueling rate modulation is not only used to
control the plasma density, but also to control the plasma energy, if
necessary, by means of isotopic fuel tailoring. Isotopic fuel tailoring
is a particular way of fueling the burning plasma which allows for
reducing the fusion power produced and, therefore, also gives the
opportunity to decrease the plasma energy when needed. The model-based
nonlinear controller is synthesized from a zero-dimensional model of
the burning-plasma dynamics. A nonlinear simulation study is used to
illustrate the successful controller performance in an ITER-like scenario
in which unknown variations of the deuterium-tritium concentration of
the fueling lines are emulated.