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

supervisory and off-normal response algorithms with provable reliability. This will include the
development and experimental qualification of control schemes and detailed real-time implementation
for nominal scenario regulation, stability control, and supervisory action with effective
and provable responses to off-normal events. The reference iteR approach to integrated plasma
control (validated models, model-based design, verification of performance) must be demonstrated
end-to-end on operating devices.
MitigatiNg tRaNSiENt EvENtS iN a SElF-hEatEd plaSMa
transient events that release plasma energy in a short period of time have the potential for causing
serious damage to plasma facing components and other structures in iteR. Preventing these
events to the extent possible and mitigating those that occur are critical in protecting the investment
in iteR as well as expediting the research program. The Fesac report entitled Priorities,
Gaps and Opportunities: Towards A Long-Range Strategic Plan For Magnetic Fusion Energy specifically
identified the control and mitigation of such transient events as critical issues for both iteR and
future fusion devices.
CuRREnt StatuS
issues
avoiding or mitigating transient plasma events in iteR is very challenging, both in the high-current
Q=10 scenario, as well as in the steady-state operating regime. in general, the preferred approach
is to avoid the initiation of a transient event that could result in unacceptable stresses or
damage to machine components. in some cases, either due to a control system failure or inability
to forecast the occurrence of a transient event, it will be necessary to take actions to reduce or
mitigate the consequences of a transient event to avoid exceeding established limits on machine
components. For example, mitigation techniques may result in terminating the plasma without
exceeding allowable stresses on the machine.
Pursuant to the Fesac panel report cited above, the following transient events for iteR were considered:
• disruptive termination of the plasma discharge, including the generation of runaway
electrons.
• large edge instabilities (edge localized modes — elms) that are associated with h-mode
operation.
• Plasma instabilities that eject large bursts of alpha particles.
all of these are important for iteR, as discussed in the ITER Physics Basis document, as well as for
demo, which will be discussed in the Theme 2 chapter.
Recent accomplishments and progress
substantial progress has been made in characterizing, predicting, avoiding, and mitigating offnormal
and transient events in existing high-performance plasma experiments. highlights include:
• suppression of disruptions with the massive gas injection technique.
51