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

esearch requirements
new facilities and/or significant upgrades of existing facilities, and extended or new codes will be
needed.
Theoretical and experimental evidence that the anomalous cross-field resistivity is related to g d
supports the hypothesis that resistivity is due to lower hybrid drift waves or a related mode. a
drift-generated resistivity from lower hybrid drift waves has been calculated theoretically and
found to explain simple theta-pinch plasma profiles. a hot, steady-state high-s experiment will
have g d < 1, may address the transport issue experimentally, and could provide a platform to study
confinement scaling. as auxiliary heating methods may alter transport, several such techniques
should be studied. effects of fast ions on transport should also be addressed. experiments need
to be supported by theory and simulation.
Plasma fluctuations associated with the diamagnetic current drift must be studied with noninvasive
diagnostics. Global confinement time studies require multi-point diagnostic systems. exploration
of this issue may be undertaken by operating the current density low enough in the high-s
experiment that the modes thought to be responsible are not excited. additional diagnostics may
be required, and additional experimental facilities may advance these studies, particularly the effects
of plasma shape and flow shear. if the resistivity is found to approach classical, new energy
and particle loss mechanisms may become dominant; it is uncertain whether the high-s facility
will continue to be appropriate or a new experiment will be needed.
CuRREnt DRiVE anD SuStainMEnt: aCHiEVE anD unDERStanD EFFiCiEnt
CuRREnt DRiVE anD SuStainMEnt OF KEV FRCs WitH gOOD COnFinEMEnt
FRc flux sustainment requires overcoming the ohmic losses associated with maintaining the diamagnetic
toroidal currents. however, the cross-field resistivity, η⊥ , is found to be anomalously
high and needs to be decreased for sustainment at low power. existing experimental facilities are
capable of studying some aspects of RmF and merging spheromaks, although the latter cannot
presently study steady-state current drive, and are limited in capability. Unless the experiment
used to study large-s is capable of long-pulse current drive and sustainment, a new experiment is
needed to extend present work and fill this gap.
research requirements
FRc toroidal current is essentially diamagnetic, so it should be possible to sustain FRc poloidal
flux by supplying enough particles deep in the core, perhaps by neutral beams. some other form
of current drive will still be required on axis. RmF could provide the current and neutral beams
might provide both current and particles.
steady-state current drive for longer than 10 ms has been demonstrated using RmF in FRcs. Fast
ions from tangentially aimed neutral beam injection were used in field-reversed mirror experiments,
resulting in significant reduction of the magnetic field and peak b > 2 but not field reversal;
however, injection into a reversed field is expected to sustain the configuration. energetic ions
also stabilize mhd modes, due partly to FlR effects but primarily as the wave-beam ion response
can be opposite in phase to the thermal plasma response, thereby reducing the instability growth
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