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

astrophic failure of internal components, can be avoided with high reliability and/or develop
approaches that allow the devices to tolerate some number or frequency of these events.
intRODuCtiOn
in Theme 1, the iteR research requirements associated with large transient or off-normal events,
which included disruptions and associated runaway electrons, large elms, and bursts of energetic
and alpha particles ejected by plasma instabilities, were described in Theme 1. The goal of this
section is to extend the research requirements to create predictable high-performance plasmas.
While the issues are similar for iteR and demo, there are both quantitative and qualitative differences
in addressing the broader issue of high-performance plasmas. Quantitatively, as will be
discussed, many of the issues identified for iteR will become more difficult assuming the same
design approaches are used for demo. Qualitatively, demo may be able to incorporate different
design strategies including the choice of magnetic configurations. These differences result in additional
research requirements to assess the potential for different solutions. in this section, the
research requirements identified in Theme 1 will not be repeated though they are, in general, applicable
to Theme 2.
in considering this, the Priorities, Gaps and opportunities Report stated:
“avoiding or mitigating off-normal plasma events in tokamaks is very challenging, particularly
in the advanced tokamak (at) performance regime (high Q, high beta, high bootstrap fraction,
steady state) anticipated for demo. The issue appears to have only two possible plasma-based solutions:
DiSRuPtiOnS
1. discover and develop improved techniques to predict and either avoid or mitigate offnormal
events in an at-regime tokamak with a high degree of confidence. a successful
demo design must provide for recovery from damage caused by low-probability offnormal
events within the availability, safety, and environmental constraints of an
economically attractive electric power source.
2. improve the understanding and performance of other confinement configurations
that either avoid off-normal events or allow more confidence in their control. a successful
non-tokamak demo design must be based on demonstrated capability of steadystate,
high-beta confinement and other properties consistent with providing the Q,
availability (including recovery from any off-normal event), safety, and environmental
features of an economically attractive electric power source. The stellarator is the most
advanced configuration that has the potential to meet these requirements.”
The severity of most consequential effects of disruptions increases for demo and beyond. electromagnetic
loadings and area/size-normalized body forces increase modestly (~3-fold) from present
tokamaks to iteR and are comparable in demo. Thus, while structural loadings associated with
the plasma current decay (or motion owed to a vertical displacement event [vde] with resulting
generation of in-vessel halo currents) increase modestly for iteR, the effects can be accommo-
99