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

this would be a burn phase, so an assessment of the reactor potential is desirable for this
concept. Research needs include extending existing simulations to have as much physics
as possible and then using the results of this research to design a new experiment. This
experiment will need at least the capabilities described in (a); both approaches might be
explored on the same facility. achieving a maximum confinement-phase pulse length
may require developing current-profile control techniques to prevent the formation of
large magnetic islands at low-order resonant surfaces in the plasma.
nonlinear macroscopic stability theory and computations with two-fluid and kinetic effects can
have a large role in testing and understanding new approaches to sustainment. however, the computational
challenges associated with modeling relaxation fluctuations increase with plasma performance
(measured by dimensionless parameters such as the lundquist number). While implicit
methods help address stiffness, they do not alleviate the need for resolving multiple temporal
and spatial scales. increasing access to computing facilities that serve communication-intensive
applications is needed. integrated simulation with self-consistently modeled radiofrequency can
be applied to profile control. The work of the Fusion simulation Project can be applied if it is sufficiently
general to include low-field configurations.
FORMatiOn: DEVELOP an EFFiCiEnt FORMatiOn tECHniQuE tO aCHiEVE
FuSiOn-RELEVant SPHEROMaK MagnEtiC FiELDS
The efficiency of spheromak formation needs to be improved. small experiments are exploring
formation techniques, but are not capable of demonstrating high efficiency due to vacuum and
other limitations, and lack of an adequate experiment is a significant gap for formation research.
computational gaps for formation studies are similar to those for sustainment studies.
research requirements
helicity injection has demonstrated the capability of generating ma spheromaks and achieving
75 mWb poloidal fluxes. however, efficiencies need to be increased significantly from the present
5%-20% as the magnetic energy is almost entirely supplied by plasma currents and needs to be
increased substantially in future research. Furthermore, the amplification of the applied poloidal
bias flux is less than ten in existing and past experiments, allowing a relatively large volume of
open magnetic field lines on the edge where ohmic losses are high. Reactor estimates indicate that
the flux amplification must be increased by almost an order of magnitude. simulations indicate
that if the bias flux and drive current are reduced together following formation, then the resulting
plasma has low losses on edge magnetic field lines and reduced instability drive at resonances
inside the separatrix; this and other innovative ideas should be explored further.
Regardless of the approach, the dissipation must be minimized to achieve an efficient ramp-up
and therefore during ramp-up the configuration must confine heat reasonably well. Ramp-up
schemes must be found that minimally affect confinement, so long as energy and helicity lifetimes
are maintained during formation. Understanding the coupling efficiency of the external
supply to the spheromak is critical to optimize buildup scaling.
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