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

ion source requirements for iteR are equivalent to those needed for steady-state, so research in
support of iteR will develop the needed technology for negative ion beam sources.
Research is needed to develop methods of handling or reducing the high neutral gas load that results
from conventional gas neutralization. The feasibility of using continuous, high-throughput
cryopumps to allow conventional gas neutralization needs to be evaluated. conventional gas neutralization
has uniform target thickness over the transverse cross section of the ion beam, which
is a consideration for other neutralization schemes.
Photo-detachment neutralization requires the development of lasers capable of continuous, highefficiency
operation and the ability to withstand neutron damage. such a system would be energy
intensive, so an engineering assessment of the benefits must be performed. Plasma neutralization
requires the development of a plasma source with high ionization fraction and uniformity across
the beam cross section. This technique must be evaluated as it may not significantly reduce the
gas loading. lithium vapor jet neutralization requires a study of the beam neutralization physics
as well as research on the lithium handling hardware. The lithium recovery system and a means to
control the impurity content in the lithium loop would need to be developed.
ST AREA 6: INTEgRATION AT HIgH BETA
Favorable operating scenarios for an st-based component test facility are projected to have low
normalized density fraction (~20-30%) and low core plasma electron collisionality n e * ~ 10 -3 , utilize
up to 50% beam-driven current fraction, operate in a plasma with ions hotter than electrons,
and with high-energy confinement operation at enhancement factors up to 50% above the
predictions for iteR. Present st experiments may have difficulty achieving normalized density
fractions below 50% and have n e * > 10 -2 – 10 -1 , have sustained only 10-15% neutral beam-driven
plasma current fraction (due to high-density operation and non-optimal beam injection geometry),
and have sustained confinement enhancements ~10-15% above iteR predictions. Potentially
more favorable energy transport mechanisms for the electrons and ions have been indicated in
present-day st experiments — accentuating the importance of understanding energy transport
in the st — especially at reduced collisionality. These core plasma parameters have not yet been
sustained for long plasma durations, i.e., for many current redistribution, pumping, or wall/divertor
equilibration times.
research requirements
based on plasma thermal confinement predictions observed thus far in nstX and mast, a factor
of 2 to 4 increase in toroidal magnetic field and plasma current is needed to access increased
plasma temperature and reduced plasma collisionality to values approaching (to within a factor of
~5) those projected for an st-ctF or an st demo. improved density control is needed to sustain
reduced collisionality, and density pumping by liquid lithium plasma facing components and/or
divertor cryopump systems should be tested to assess the accessibility of a low normalized density
fraction in st-ctF-relevant integrated scenarios. sufficiently high bt ≥ ~15% at reduced collisionality
is needed to develop an understanding of the underlying causes and scalings of electron
(and ion) transport in high normalized pressure (high-b) st regimes and in compact high-b
systems generally. enhanced gyrokinetic turbulence simulation capabilities are needed to under-
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