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

Scientific Issues and research requirements
Three primary challenges need to be addressed in the iteR era: (1) formation and stability in the
fusion-plasma regime, (2) transport and energy confinement, and (3) efficient current drive and
flux sustainment. The FRc and spheromak operate in significantly different physics regimes, so
the issues and Research Requirements for the two configurations are discussed separately. additional
sections consider diagnostics, theory and modeling, and reactor studies for cts. tables 3
and 4 at the end of the section summarize the needed facilities and the theory and codes to handle
the research requirements discussed below.
Connections to Broader Science
The cts are closely coupled to a wide range of broader science. They extend fusion plasma science
to very low aspect ratio and minimal external magnetic field, with no toroidal field coils. The FRc
has no toroidal field in the ideal limit, and the magnetic winding (“safety”) factor of the spheromak
lies between the tokamak and RFP. a magnetic dynamo drives the spheromak toward a selforganized
state in a complementary way to the RFP; in both, this science is closely related to processes
in space and astrophysics. much of the research is done in universities and the configurations
lend themselves to the “discovery science,” which may provide transformational ideas in the
search for fusion energy.
FRC
StabiLity at LaRgE S: aCHiEVE gLObaL StabiLity at LaRgE S in LOW
COLLiSiOnaLity FRCs. (S IS THE NUMBER OF ION LARMOR RADII BETWEEN THE
CENTRAL FIELD NULL AND THE SEPARATRIX)
The highest priority issue for the FRc is maintaining stability as the size is scaled up and the plasma
becomes more mhd-like. in the largest theta-pinch FRc, the large s experiment (lsX), hot, highdensity
stable FRcs were formed with s up to 4, but s ~ 20 or more will likely be needed for reactors.
cold plasmas in ssX had s ~ 10 and were unstable at slower than mhd growth rates. The most worrisome
FRc instability, the n=1 axial tilt, is external in oblate FRcs and can be stabilized by closefitting
conducting walls or strong external field shaping. in prolate FRcs the mhd-tilt is internal,
and other stabilizing means are needed. experiments and simulations to address this issue can be
handled in part by existing facilities and codes, but their capability falls short of the requirements to
resolve it. The limitations of existing simulations and experiments constitute a major research gap.
research requirements
new facilities and/or significant upgrades of existing facilities and extended or new codes will be
needed. The parameters of the required experimental facilities include:
• low-collisionality FRc plasmas with sufficient flux to confine fast ions, ~ 20-50 mWb.
• efficient heating and current drive methods.
• Fast ion creation at mid to lower 10 19 m -3 densities, possibly by neutral beam injection, to
generate large fast ion-ring currents for stabilizing effects and for current drive if needed.
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