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

Medium-term: Test and optimize fully integrated comprehensive early detection and recovery control
options of plasma-induced disruptions and external hardware system failures in long pulse D-D plasmas
at progressively higher pressures. Consider implementation of novel disruption avoidance techniques.
Long-term: Extend the integrated control scheme for the full range of early detection, recovery without
shutdown, mitigation, recovery with controlled shutdown, cleanup, repair, and reconditioning options
in ITER to dominantly alpha-heated, self-sustained D-T plasmas.
Key Most Difficult Challenges
Following is a brief summary of the challenges in this Thrust that are considered most serious:
Active steady-state control: development of diagnostics required for accurate equilibrium reconstruction
capable of surviving in a high-fluence environment. development of steady-state,
high-efficiency, high-power heating and current drive systems for plasma sustainment, current
profile control and mhd stabilization that can be scaled to a high-fluence reactor environment.
development of efficient actuators for controlling the density and temperature profiles in a largely
self-determined alpha-heated system. development of robust control algorithms in regulating
and sustaining steady-state fusion plasmas with highly coupled, high-dimensionality nonlinear
dynamics.
Startup and shutdown: development of scenarios for startup to fully noninductive state in an
alpha-dominated heating environment. These are not presently known and require study in iteR.
Burn control and thermal stability of the operating point: development of advanced steadystate
fueling techniques, for deep fueling in reactor-grade plasmas. development of a suitable
technique for selectively removing alpha particle ash.
Robust active stabilization of instabilities and transient fluctuations: development of
shielding strategies in conjunction with options for optimizing far-placed coils, or other control
techniques. internal coils and sensors for RWm and elm control may be precluded in the highfluence
nuclear environment of a power-producing reactor, so other options need to be explored
and developed.
Regulation of the power flow distribution to material surfaces: development of a working
target divertor solution that scales to a reactor is a prerequisite for developing a control system.
sufficient understanding of heat and particle transport across the plasma separatrix and into the
divertor, and its dependence on the edge profiles and plasma fluctuation amplitudes and frequencies,
is currently lacking.
Active prediction, avoidance, detection, and response to disruptions and fault events: development
of schemes for controlled recovery and mitigation of off-normal events that can be reliably
scaled and avoid additional negative consequences. This advance would critically improve
the reliability of a power producing reactor, but will require a concerted long-term research program
with testing at each level.
274