Zero-dimensional Nonlinear Burn Control Using Isotopic Fuel Tailoring For Thermal Excursions
M. D. Boyer and E. Schuster
IEEE Multi-conference on Systems and Control
Denver, Colorado, September 28-30, 2011
Abstract
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The control of plasma density and temperature are among the most
fundamental problems in fusion reactors and will be critical to the
success of burning plasma experiments like ITER. While stable burn
conditions exist, it is possible that economic and technological
constraints will require future commercial reactors to operate with
low temperature, high density plasma, a burn condition that may be
unstable. The instability is due to the fact that for low temperatures,
the fusion heating increases as the plasma temperature rises. An
active control system will be essential for stabilizing such operating
points. In this work a spatially averaged (zero-dimensional) nonlinear
transport model for the energy and the densities of deuterium and
tritium fuel ions, as well as the alpha- particles, is used to
synthesize a nonlinear feedback controller for stabilizing the burn
condition of a fusion reactor. Whereas previous efforts assume an
optimal 50:50 mix of deuterium and tritium fuel, this controller makes
use of ITER’s planned isotopic fueling capability and controls the
densities of these ions separately. Also, unlike previous work which
used impurity injection to mitigate thermal excursions, this design
exploits the ability to modulate the DT fuel mix to control the plasma
heating. By moving the isotopic mix in the plasma away from the
optimal 50:50 mix, the reaction rate is slowed and the alpha-particle
heating is reduced to desired levels. A zero- dimensional simulation
study is presented to show the ability of the controller to bring the
system back to the desired equilibrium from a given set of
perturbations.