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

in the PFcs, can be accurately extrapolated to demo. There is an extremely large range of potential
time scales to examine, spanning from a few seconds for recycling equilibration (tungsten at
1000k), of order an hour for the fuel to equilibrate with the full PFc thickness (5 mm thick tungsten
at 1000k), of order a day for erosion and redeposited thicknesses to reach 100 microns, and
of order a month to erode through half the PFc thickness. longer pulses with high duty factor will
be highly advantageous, if not necessary, for studying critical physics and operational issues such
as elm and disruption avoidance, and dust production and removal. Relatively short pulses with
high repetition rate may be the least costly to achieve, but the large number of thermal cycles required
to study the high fluence issues may compromise the scientific and technical results. The
determination of the optimal pulse length and duty factor for this device will require examination
of the trade-offs of cost and reliability versus the issues to be studied.
The new data from this Thrust will be a primary resource for validation of the models that will
be developed as part of Thrusts 9 and 10 that are needed for designing demo boundary components
and operation. model validation requires measurements to fully characterize the plasma
and plasma-material interactions. This implies 2-d measurement of the plasma state, including
density, temperature, power accounting and impurities. measurements must also include full coverage
of surface properties, including temperature, surface composition, erosion and redeposition
rates, along with accounting of retained fuel. This requires extremely good diagnostic access,
which must be part of the design from the start.
a key mission of this Thrust is validating the integrated performance of the material boundary
with the core plasma in demo-like conditions. The output of Thrusts 2, 5, 9, 10 and 11 will be a
number of promising PFc configurations, and control scenarios and actuators, that will have to
be tested in an integrated fashion in this facility. it is therefore necessary that this facility feature
flexibility for ease of multiple hardware changes driven by the broad testing program. in particular,
this facility will undergo modifications in PFc technology and materials, boundary and divertor
heat bearing configurations, actuator systems for control of the steady-state plasma and
transients (elms and disruptions), and associated diagnostics to monitor all these systems. This
flexibility is further needed to allow for unforeseen modifications, due to our present limited understanding
of boundary and core plasma issues as well as the first-wall technology and their interaction.
in summary, this facility should be capable of testing and validating the full variety of
configuration options that can be applied to devices on the path to demo.
While complete boundary solutions must be employed and tested in a high-power d-t facility,
the variety and number of issues to be addressed for the boundary and its interaction with the
core plasma can be more readily examined in a limited activation environment. such operation
will have a number of advantages in carrying out this research. First, the lower levels of radiation
will allow for greater access for flexibility to change out the variety of components, systems and
configurations that must be tested. a limited activation environment would also provide a less
harsh operating environment for diagnostics. Finally, the entire device scale and design will not
be driven by the requirement to achieve high fusion power gain.
There are significant tradeoffs associated with the level and timing of deuterium operation, since
activation by d-d neutrons will be a concern. While hydrogen operation would produce a mini-
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