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

Figure 1. Upgrades and smaller experiments (CE) contribute to the advanced proof-of-principle (PoP) experiment
in the RFP development path.
temperatures in mst, the only operating RFP in the Us. The RFX-mod experiment in italy and
extrap t2R in sweden have demonstrated active control of multiple external modes to an unprecedented
degree in magnetic fusion research. RFX-mod also shows an increasing likelihood of a
quasi-helical state with improved confinement as the current is increased. The proposed development
path shown in Figure 1 builds on these results to address concept needs.
1. Upgrading power supplies for mst can increase the maximum plasma current, possibly
above 0.6 ma, decreasing r* and increasing central S-value to 4×10 7 . This improvement
will help distinguish strong scaling of magnetic fluctuations (~S -1/2 , argued theoretically)
from weak scaling (~S -1/5 , obtained at low-S in experiment and simulations). if the
additional power reduces edge resistivity, ac current drive can be tested at a substantial
level. initial tests of a hybrid operating scenario using ac drive and self-similar decay will
also be possible. new diagnostics, such as spectral motional stark effect and fast Thomson
scattering, will improve the accuracy of profile reconstruction and enable fluctuation
studies. installation of a 1 mW neutral beam injector will improve current profile control,
allowing transport analysis in magnetically quiescent conditions. it will also provide
heating to test stability limits with significant energetic-particle b.
2. Physics and engineering research for RFP boundary control will consider the technology
required to spread heat loads from nearly poloidal magnetic field. Particular boundary
control solutions need to consider coupled physics effects, and may benefit from recent
advances in low recycling walls.
3. a study to optimize the RFP geometry will lead to more complete knowledge of fluctuations
and effects that influence their scaling. an effort to minimize the deleterious effects of
resonant fluctuations can begin with theoretical computations. asymmetric shaping may
increase the probability of quasi-helical states. aspect ratio optimization, pursued by the
RelaX group in Japan, will provide information on bootstrap current and mode coupling.
information from upgrades, new concept exploration (ce) experiments, and theory will
influence the design of the advanced experiments described in the following task.
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