Control-Oriented Core-SOL-Divertor Model to Address Integrated Burn and Divertor Control Challenges in ITER
V. Graber and E. Schuster
Symposium on Fusion Technology (SOFT)
September 18-23, Dubrovnik, Croatia, 2022
The real-time regulation of a burning plasma's temperature and density,
or burn control, will be necessary to produce high fusion power in future
tokamaks like ITER. This is made more challenging due to the plasma's
nonlinear characteristics and the interdependence between the core-plasma
and edge-plasma regions. For example, a raising plasma temperature leads
to increasing reactivity and therefore to more alpha-particle heating,
which further increases temperature. Furthermore, a raise of the fusion
power increases the heat flow through the scrape-off-layer (SOL), which
can compromise the integrity of the divertor without proper safeguards.
For control design, a model-based approach is attractive because it can
directly incorporate the nonlinear, coupled, burning-plasma dynamics
into the design. To facilitate this design approach, a control-oriented
core-SOL-divertor (CSD) model is presented in this work. In this CSD
model, a core-plasma model captures the nonlinear dynamics of the core's
density and temperature, and a SOL-divertor model defines the plasma
conditions at the separatrix and divertor including the heat load on
the target plates. The core-plasma and SOL-divertor models are coupled
through the exchange of various variables. In particular, the SOL-divertor
model yields the separatrix temperature and the influx of recycled particles
into the core-plasma. These variables influence the power and particle
balances captured by the core-plasma model. In return, the core-plasma
model determines the intensity of the heat and particles fluxes across
the separatrix, and this outflow strongly impacts the SOL-divertor model.
Therefore, the power and density of the core-plasma, which can be readily
modulated through external heating systems and pellet injection, can be
viewed as control knobs for the SOL-divertor region in addition to the
gas puffing. In simulations of the CSD model, it is demonstrated how
external actuation can be utilized to meet burn control and divertor
control objectives simultaneously.
*Supported by the US DOE under DE-SC0010661.