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

Figure 12. The application of non-axisymmetric fields in the plasma edge region, as indicated by the nonzero
current I in the I-coil, is a promising technique to suppress ELMs, as shown in DIII-D experiments. (Figure
courtesy of T.E. Evans; for a related article, see Nature Physics 2 [2006] 419.)
• determine the perturbed field requirements to control elms over a broad range in q.
• determine the requirements for avoiding deleterious nonresonant fields.
• evaluate the compatibility of core pellet fueling with the application of non-axisymmetric
fields.
• develop magnetic coils that can operate inside the iteR vacuum vessel, where the coils
are exposed to high neutron fluence and require remote maintenance.
eLM-free operational regimes
The development of operating regimes with the occurrence of beneficial edge instabilities to control
the edge pressure gradient and avoid the onset of elms is an active area of research, resulting
in the discovery of quiescent h-mode (Qh) and enhanced d a (eda) modes of operation. an
alternative strategy is to develop improved confinement regimes with a low-confinement mode
(l-mode) edge. Research needs in this area include:
• identify the underlying mechanisms responsible for the edge instabilities in the Qh and
eda modes of operation and determine if these can be used on iteR.
• identify tools to control the edge instabilities and pedestal parameters. The edge
instabilities are needed to avoid the accumulation of impurities and density build-up in
h-mode discharges, which are elm-free.
• in improved confinement regimes with an l-mode edge, assess whether the lower edge
pressure gradient is compatible with an increased peaking factor without degradation of
the plasma ideal beta limit.
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