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

Scenario optimization
The experimental goal of research in the area of core dynamics in a D-T plasma is to determine if we can
attain the plasma parameters required for a fusion power plant. What is the most attractive core
burning plasma regime that can be achieved?
The external control of a high-performance plasma core will become progressively more difficult,
relying on the self-organization of the plasma. as the ratio of self-heating to applied heating
P alpha /P input becomes larger, the external heating sources become a weaker contribution, tending
to be only one-fifth to one-tenth of the total power into the plasma. as the plasma density
increases, as it must to generate large fusion powers, the current drive from external sources becomes
a smaller fraction of the total plasma current, also about one-fifth to one-tenth , while the
self-generated bootstrap current dominates. There is expected to be a net loss of diagnostics compared
to those typically found on experimental tokamaks today, as the neutron fluence and power
levels increase. a strong reliance on simulations to replace critical measurements is expected to
emerge. multi-level feedback systems would be required on a level beyond that on present tokamaks
or even iteR to control the many coupled parameters. Understanding how high a core plasma
performance is consistent with a stable and sustainable plasma configuration is a major goal
of integrated core plasma studies.
Role of predictive capability in extrapolation to DEMO
Demonstrating plasma parameters at the same level as a fusion power plant (DEMO) is not possible without
building the power plant. Therefore, parameters will be demonstrated only up to some level, likely not
at precisely the same as a power plant, and often in isolation and not all simultaneously. What DEMO
parameters can we demonstrate dimensionally or non-dimensionally, and what sets can be
demonstrated simultaneously in a given D-T burning experiment?
This aspect leads directly to the importance of predictive theory and simulation, to bridge the gap
from the final pre-demo device to demo. here we emphasize the closing window of opportunity
to establish a sufficient level of predictive capability. to validate theory and simulation on experiments,
advanced diagnostic techniques are required, such as turbulence fluctuation diagnostics,
to provide a detailed measurement to compare to a simulation. as the environment in a d-t
tokamak becomes more severe from high neutron and plasma loads, many of these diagnostics
cannot be utilized. as the most sophisticated diagnostics disappear, the ability to make the most
direct comparisons with theory and simulations will also diminish. The full use of d-d tokamaks
(including the long pulse asian devices) and the low fluence iteR d-t tokamak will be critical to
establishing a simulation capability that is required to make the step to demo. This is discussed
further in this Theme.
It is expected that the size of the gaps in demonstrating DEMO-level plasma parameters experimentally,
and the confidence in validated simulation for extrapolating across such gaps, will vary, requiring careful
planning for proposed devices and physics theory and simulation development. How do we plan predictive
simulation developments and experimental developments to simultaneously minimize
projections to DEMO?
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