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

• develop new diagnostics for internal oscillations and eP profile measurements in st
plasmas to establish the database of eP loss and transport, for both present-day and
next-step sts.
• engage in theoretical investigation of the interaction between multiple alfvén modes
and the background plasma. measure the alfvén mode structure and the effects of these
modes on thermal ion heating and electron transport. investigate their control using
external antennas as a possible means to control the channeling of the eP energy into
thermal electron/ion energy.
Links to other thrusts: Theme 1, burning plasmas and itER: alpha particles; Theme 2,
high-performance steady state: validated modeling (Thrusts 3, 6)
4. Implement and understand active and passive stability control techniques to enable long-pulse
disruption-free operation in plasmas with very broad current profiles.
maintaining the continuous high-pressure plasma operation required for efficient st-ctF and
demo operation at a low level of neutron fluctuation and plasma disruptivity requires an understanding
of stability and control at reduced levels of collisionality, and broader current profiles,
than attained in present devices. a spherical torus component test facility will not perform this
research, so understanding must be developed, and performance levels reached now, for both
ctF and demo-class applications. compared to tokamaks, the st operates in a unique parameter
regime of very low internal inductance, high pressure normalized to magnetic field (beta), and
high ratio of fast ion to alfvén velocity. Physical effects in this regime, including distinct global
instability structures, increased multi-mode effects, explicit geometric dependence of neoclassical
tearing mode (ntm) stability, and magnetic control of plasma rotation, require dedicated st
research.
actions:
• Reduce the plasma internal inductance via broader neutral beam injection/radiofrequency
current deposition and/or lithium walls, aiming for self-consistent current profiles to test
kink/ballooning and resistive wall mode (RWm) stability near the current-driven kink
limit. assess elevated safety factor q > 2 for ntm stability and provide a wide range of
accessible beta since the current-driven kink may be unstable at any normalized beta, and
multiple modes may be important at high normalized beta.
• Reduce plasma collisionality up to an order of magnitude utilizing st device upgrades to
test theoretical RWm stabilization and the expected increase of nonresonant magnetic
braking.
• develop control of the plasma rotation and shear using expanded nbi and nonresonant
magnetic braking capabilities to understand the effect of rotation and shear on RWm and
ntm.
• implement expanded active RWm feedback control (e.g., non-magnetic sensors, multimode
capability, upgraded 3-d control fields), dynamic error field correction, moderate
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