Assessment of the Burning-Plasma Operational Space by Using a Control-Oriented Core-SOL-Divertor Model
V. Graber, E. Schuster
Symposium on Fusion Technology
Remote, September 20-25, 2020
In future tokamaks, the control of burning plasmas will require careful
regulation of the plasma density and temperature. Along with the design
of effective burn-control systems, understanding how the fusion power
varies in the density-temperature space is vital for the operation of
fusion power plants. In this work, the steady-state operational space
of ITER is studied using a control-oriented core-plasma model coupled
to a two-point model of the scrape-off-layer (SOL) and divertor regions.
The two models are coupled through the exchange of input-output parameters.
The fuel recycling and impurity sputtering from the divertor are output
parameters of the SOL-divertor model that are used as input parameters
in the core-plasma density balance. Furthermore, the separatrix temperature,
which is an output parameter of the SOL-divertor model, is incorporated
into the radial core-plasma temperature profiles. Therefore, the
temperature-dependent power balance of the plasma core is intimately
linked to the SOL-divertor model. Both the power entering the SOL from
the core, as determined by the core-plasma power balance, and the
separatrix density, as dictated by the core-plasma density balance, are
input parameters to the SOL-divertor model. They are control knobs in
the SOL-divertor model that can be regulated using the core-plasma
actuators: auxiliary power and pellet injection. There are various
operational limitations, such as the saturation of the aforementioned
actuators, that will prevent ITER from accessing certain high-fusion
plasma regimes. The achievable tritium concentration in the fueling
lines and the maximum sustainable heat load on the divertor will impose
further restrictions. By accounting for these limitations, the ITER
operational space is computed based on the coupled core-SOL-divertor
model and visualized using Plasma Operation Contour (POPCON) plots that
map performance metrics, such as the fusion to auxiliary power ratio,
over the density-temperature space. Comparisons are drawn between plasmas
with different recycling, confinement, and SOL-divertor conditions.