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

ion losses, a quantitative prediction for the alpha loss rate and the distribution of the lost alphas
is not yet available. Predicting the magnitude, frequency, and localization of the losses is important
for the design of the plasma facing components. likewise, it is necessary to understand the
resilience of tungsten or other plasma facing components that are affected by lost alphas against
the combination of high-transient power loads and high-alpha fluence. Research needs in this
area include:
• determine the thresholds for tae avalanche, fishbone, and related ePm stability, and
compare with linear and nonlinear theory, including gyrokinetic effects.
• benchmark predictions from simulation codes of fast ion losses in the presence of mhd
mode activity against experimental measurements of mode amplitudes, profiles and
frequencies and measured fast ion losses and redistribution. This should be done for all
forms of mhd instabilities that might cause fusion alpha losses.
• measure fast ion deposition profiles on divertor tiles and other plasma facing components,
and compare with the predictions from simulation codes.
• improve the understanding of material damage due to alpha-particle bombardment.
Present experimental facilities, together with the application of new codes under development,
could be used to develop a predictive capability for energetic particle losses in iteR. test stand experiments
are needed to study the effect of alpha particle bombardment.
diagNoSiNg a SElF-hEatEd plaSMa
The ability to make accurate measurements on hot, magnetically confined plasmas has driven
much of the understanding and progress to date in the fusion energy sciences field. similarly,
accurate measurements are required in iteR, not only to facilitate control of plasma quantities
to achieve burning plasma conditions, but also to obtain information about burning plasma behavior
that is important for future applications (see Figure 13). high-quality measurements on
iteR will be more challenging than on present-day devices due to the neutron-rich environment
in which diagnostics must operate, which will require the development of new diagnostic techniques.
The deployment of these diagnostics will likely pace the development of the knowledge
of burning plasma physics, for “The required progress in key areas will not be possible without a
significant expansion of our diagnostic capabilities. Quite simply, we cannot understand what we
cannot measure.” 1
CuRREnt StatuS
issues
as we proceed toward creating burning plasmas in iteR and, beyond that, toward creating steadystate
high-performance burning plasmas, there are major challenges at each step for making the
necessary measurements. in its report analyzing the issues and gaps for fusion research arising
in a path to demo, the Fesac “Greenwald Panel” identified the need for measurements that will
1 Plasma Science: Advancing Knowledge in the National Interest, National Academy Press (2007), p
120.
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