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

esearch requirements
key research needs to support the st iteR-era goal divide into areas of: (1) plasma initiation and
ramp-up, largely or entirely generated without a central solenoid due to st space restrictions, (2)
plasma-material interface, handling the uniquely high heat fluxes found in the inherently compact
st design, (3) understanding of energy transport — especially of the plasma electrons —
which dominates in present high-performance st devices, (4) stability and steady-state control
for continuous operation at the high normalized pressure (beta) and with very broad current profiles
of st plasmas, at low levels of stored energy fluctuation, (5) technological development to
support unique st challenges including magnet technology, and (6) integration of the elements
to demonstrate plasma sustainment and understand the interactions of the components for confident
extrapolation to st-ctF and demo. This collection forms a group of research thrust elements
(see Thrust 16) with the twelve individual Fesac taP critical issues included in these elements.
advancements in theory and modeling, critical to this plan, are integrated into the research
requirements. no priority is implied by subject ordering.
ST AREA 1: PLASMA CURRENT INITIATION AND RAMP-UP
Plasma initiation and ramp-up techniques for the st need to further advance by largely or entirely
supporting this process without a central solenoid to generate plasma current.
initiation by maGnetic helicity inJection
research requirements
driving current parallel to externally applied magnetic fields, by applying a voltage to electrodes
on the magnetic field lines, can generate plasma current by magnetic turbulence (a technique
called magnetic helicity injection — hi). Research focusing on understanding the mechanisms
that limit the achievable current and on determining the characteristics of the resulting plasma is
needed. This requires dedicated experiments on sts with direct current hi capability (from localized
“point” sources, and toroidal “coaxial” electrodes) and comparison to theory-based physical
models. experimental hi research is needed to develop local current plasma sources that provide
very high current density, as well as toroidal metal electrodes that minimize plasma impurity
content and simpler insulator configurations that are more easily adaptable to future sts. testing
coaxial configurations would also benefit point source hi.
specific topics required for hi study include current, particle, energy, and momentum transport
across magnetic fields in a turbulent system and the role of flows (due to strongly biasing the plasma
edge) on the plasma equilibrium, stability, and transport as the plasma forms and evolves. of
particular interest is assessing the applicability of simple steady-state, two-dimensional models
in describing an inherently three-dimensional dynamic system. accurate predictive capability
of the resulting plasma characteristics is needed to assess coupling to alternative current drive
methods to further increase the plasma current to required levels. These validated models are
needed to determine the required noninductive current drive capability of future st designs.
Plasma current initiation via external magnets (outer poloidal field induction) in conjunction
with hi and radiofrequency techniques can be assessed in existing and upgraded facilities. initia-
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