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

Develop the means for and demonstrate regulation of the power flow distribution to material
surfaces in the presence of core plasma transients, while keeping each component within
acceptable tolerances: What level of regulation of the power flow distribution can be achieved in
the presence of fluctuations from plasma transient events?
The power flow from a fusion reactor must be in a useable form and is limited by the capability of
materials to handle the influx of radiation, neutrons, heat, and energetic charged particles. The
spatial and temporal distribution of each of these components needs to be controlled sufficiently
to avoid exceeding local material limits.
Specific Challenges:
The different elements comprising the power flow have different spatial distributions. Radiation
and neutron fluxes are essentially volumetric sources and absorbed by the first wall and shielding.
The heat flux from thermal particles is largely directed to specific target divertor plates by
the plasma edge magnetic geometry. With current technology, the power flux allowable on divertor
plates is ~10 mW/m 2 and is normally most limiting. Reliable control is needed to balance and
maintain the various fluxes at manageable levels in the presence of temporal fluctuations from
plasma instabilities — notably sawteeth and elms, but also from other sources. Presently envisaged
solutions for iteR using radiative divertors, for example, may not be sufficient for demo.
a search for solutions is a primary aim of Thrusts 9 and 12. implementation of these solutions in
a high-performance steady-state system is a major challenge for this Thrust.
as discussed earlier, the actuators for maintaining and controlling the equilibrium state indirectly
control the power flow distribution. control of the power flow requires sufficient confidence
in understanding the dependence of transport on the equilibrium configuration and various
fluctuations that control-level models of this dependence can be extracted. Presently there
are serious gaps in the required understanding, especially in the edge region and in the presence
of elms. Precise control of the magnetic field strike points at the divertor, and of detachment
of the radiating divertor, is crucial. diagnostics for the divertor region and for fast ion outflux
require major development. The control system is needed to balance the requirements of maintaining
the power flows within acceptable tolerances and minimizing the recirculating power required
by the actuators. This necessitates developments in control algorithms coupled with understanding
of the limitations and capabilities of sensors and actuators, as well as the interrelations
between the plasma equilibrium, amplitudes and frequencies of transients, and the resulting
power fluctuation levels.
Research Plan:
Short-term: Develop the control required to implement divertor solutions, obtained in Thrusts 9 and 12,
in existing experiments that can scale to reactor conditions.
Medium-term: Test elements of the control system for regulating power flow in a steady-state D-D environment
with divertor control and fluctuation detection and response.
272