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

esearch requirements
analysis of neutral beams to drive optimized current profiles is underway, but experiments will
be needed to verify predictions before large-scale applications. as known from tokamak research,
possible detrimental effects also need consideration. energetic particles produced by neutral
beams and fusion reactions can resonate with alfvén eigenmodes and affect their stability. Relative
to thermal particles, trajectories and confinement of energetic particles are much less sensitive
to global magnetic fluctuations, but a quantitative assessment of the coupling is needed. interaction
of energetic particles with tearing instabilities is a new area of theoretical research and
may have important, possibly beneficial, consequences.
RESiStiVE WaLL MODES: DEMOnStRatE RESiStiVE WaLL MODE COntROL
The tilt and shift modes in existing spheromaks are controlled by flux-conserving walls, but for
long-pulse or steady-state operation these instabilities will become resistive wall modes. no present
facility is capable of addressing resistive wall physics in spheromaks.
research requirements
as in the RFP, macroscopic instabilities are sensitive to the location of a conducting wall and become
violently unstable without a wall. The modes also are unstable when discharges exceed the
time required for magnetic perturbations to diffuse through walls of finite conductivity. effective
feedback schemes for resistive walls and simultaneous, multiple mhd modes have been demonstrated
experimentally on the extrap-t2 and RFX-mod RFPs. This is encouraging for the spheromak,
but an experimental confirmation of control is needed. The role of plasma rotation and rotational
shear in stabilizing resistive wall modes in the spheromak also needs evaluation.
incorporating thin-shell and external vacuum models is a tractable numerical approach for resistive
wall studies, and simulation of feedback stabilization needs time-dependent sources. damping
for rotational stabilization may require sound wave damping or other kinetic effects.
tECHnOLOgy: DEVELOP tHE tECHnOLOgy FOR LOng-PuLSE OPERatiOn.
technology development is presently done as needed for specific experiments, but will need to be
addressed more systematically for future, fusion-level experiments.
research requirements
helicity injection technology will need considerable development to handle steady-state conditions
including heat loads if it continues to be used for spheromak sustainment. current drive
techniques are likely to have specific technology requirements that differ in part from those in tokamaks.
Wall properties do not appear to limit performance at present, but are likely to need improvements
to handle heat loads and other long-pulse issues. options for divertors appear promising
but need development. new facilities will be required. it is premature to define them at this
time.
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